U-Th Dating of Zircons from a Holocene Volcanic Eruption (Dayingshan Volcano, 
Tengchong Volcanic Field):  Insights into Magma Chamber Storage 
 
by 
 
Ross Thomas Tucker 
 
 
 
 
A thesis submitted to the Graduate Faculty of 
Auburn University 
in partial fulfillment of 
requirements for the Degree of 
Master of Science 
 
Auburn, Alabama 
August 6, 2011 
 
 
 
 
Copyright 2011 by Ross Thomas Tucker 
 
 
Approved by 
 
Haibo Zou, Chair, Assistant Professor of Geology 
Mark G. Steltenpohl, Professor of Geology 
Willis E. Hames, Professor of Geology
 
 
 
 
 
 
 
 
 
 
ii 
 
Abstract 
 The Tengchong volcanic field is located along the southeastern margin of the 
Tibetan Plateau and has shown active volcanism throughout the Cenozoic.  Only three 
volcanoes, however, have erupted more recently in the Holocene.  The source of this 
volcanism is poorly understood due to several unique eruptive stages.  The Holocene 
volcanic rocks derive from a potassic melt with high SiO2 content (62 wt. %) and an 
abundance of zircon grains.  Zircon is renowned for its important role in geochronology 
and crustal evolution studies.  This research utilizes U-Th dating methods and secondary 
ion mass spectrometry to date zircons from the Dayingshan volcano, which can be used to 
provide constraints on magma chamber storage time. 
 Whole-rock major and trace element analyses from Dayingshan indicate high Zr 
concentrations and a calc-alkaline suite.  Trace elements plotted on a spider diagram reflect 
magma generation involving hydrous fluids in the mantle overlying a downgoing 
lithospheric slab.  Measured zircon cores yielded an age of 87.5 ? 6.5 ka, while zircon rims 
yielded an age of 58 ? 13 ka.  These different ages represent two separate magmatic events.  
The older age population is interpreted as antecrysts remobilized from an earlier magmatic 
episode.  The calculated magma chamber storage time for the most recent Dayingshan 
eruption is 48 ka.  Trace element and isotopic data suggest hydrous melting of a stagnant 
slab from earlier subduction as the likely cause for the continental crust signatures of the 
magma. 
iii 
 
Acknowledgments 
 Funding for this research was graciously provided by Haibo Zou via a National 
Science Foundation (NSF) grant (EAR-0917651).  Funding for travel was provided by the 
Auburn University College of Science and Mathematics.  Axel Schmitt provided guidance 
and instruction on the operation of SIMS.  Thanks are owed to him, Kevin McKeegan, Mark 
Harrison, and all others who participated in the NSF National Ion Microprobe Student 
Workshop hosted by UCLA.  Thanks are owed to Clint Barineau and Columbus State University 
for providing the facilities and equipment for zircon extraction, as well as valuable instruction on 
the zircon extraction process.  Special thanks are owed to Haibo Zou for providing funding, 
materials, valuable insights into the field area, assistance in sample preparation, and instruction 
on the operation of SIMS.  Thanks are also owed to thesis committee members Mark Steltenpohl 
and Bill Hames for their valuable suggestions and comments that improved the quality of this 
thesis.  Finally, thanks are owed to my parents, Tom and Becky Tucker, for providing every kind 
of support throughout my undergraduate and graduate studies.  
 
 
 
 
 
 
 
 
 
 
 
 
iv 
 
Table of Contents 
 
Abstract.........................................................................................................................................................................ii 
Acknowledgments...................................................................................................................................................iii 
List of Tables..............................................................................................................................................................vi 
List of Figures...........................................................................................................................................................vii 
Introduction.................................................................................................................................................................1 
Objectives.....................................................................................................................................................................4 
Background..................................................................................................................................................................5 
 Geologic Setting...........................................................................................................................................5 
 Concerning Zircon......................................................................................................................................8 
 Uranium-Series Radiometric Dating...............................................................................................14 
 Secondary Ion Mass Spectrometry (SIMS)....................................................................................17 
Previous Work.........................................................................................................................................................24 
Methods......................................................................................................................................................................26 
 Zircon Extraction.....................................................................................................................................26 
 Sample Preparation................................................................................................................................27 
 Cameca ims 1270 Analytical Methods............................................................................................30 
Results.........................................................................................................................................................................53 
 Dayingshan Whole-Rock Major and Trace Element Analysis...............................................53 
 Polished Zircon Core Ages...................................................................................................................58
v 
 
  Unpolished Zircon Rim Ages...............................................................................................................62 
 Comparison of Core and Rim Ages???????????????????????????62 
 Zircon Saturation.....................................................................................................................................66 
Discussion..................................................................................................................................................................68 
 Magma Chamber Storage Time..........................................................................................................68 
 Th/U Ratios................................................................................................................................................70 
 Comparison of Dayingshan and Maanshan Data........................................................................71 
 Assessment of Magma Origins...........................................................................................................73 
Conclusions...............................................................................................................................................................75 
References.................................................................................................................................................................77  
vi 
 
List of Tables 
 
 
Table 1.  The four stages of Tengchong volcanism and some characteristics.  Distribution 
data is from Zhu et al. (1983).  With the exception of stage 3, there is an increasing trend in  
K2O and SiO2 content through time (Zhu et al., 1983)..............................................................................7 
 
Table 2. Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. 
is the standard error, which represents measurement uncertainty.  Background is  
measured at 246.3 and 244.038, respectively...........................................................................................34 
 
Table 3.  Major and trace element concentrations from Dayingshan whole-rock analysis of  
sample YTC9724-5.................................................................................................................................................54 
 
Table 4.  U/Th isotope data, concentrations, and ages for Dayingshan zircon cores as  
measured by SIMS. 1s is the standard error and is a measurement of uncertainty.......................60 
 
Table 5.  U/Th isotope data, concentrations, and ages for Dayingshan zircon rims as  
measured by SIMS. 1s is the standard error and is a measurement of uncertainty.......................64 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
vii 
 
List of Figures 
 
Figure 1.  Location map of the Tengchong volcanic field in SE China.  TVF lies in a N-S 
trending fault zone between the Sagaing and Red River faults, and lies ~200 km from the  
subduction-related Burma volcanic arc (From Zou et al., 2009).....................................................2 
 
Figure 2.  Distribution and relative ages of the three most recently active volcanoes and 
surrounding rocks.  Most volcanoes represented are small cinder cones (Modified from Zou et  
al., 2009)..........................................................................................................................................9 
 
Figure 3.  Photomicrographs of Dayingshan basaltic andesite.  A) 4X view showing large 
phenocrysts of olivine (middle center) and plagioclase (bottom center).  B) 10X view of the  
groundmass showing mostly plagioclase laths in a dark matrix.......................................................10 
 
Figure 4. Distribution of depositional units deposited by multiple eruptive events from 
Dayingshan volcano.  I is the oldest flow, and V is the youngest.  A small lava lake has  
developed to the northwest of the scoria cone (From Wei et al., 2002)........................................11 
 
Figure 5.  238U decay chain depicting either alpha or beta decay into several intermediate isotopes 
before the final stable 206Pb isotope is reached.  N = atomic number;  Z = atomic mass ( From  
Berg, 2008)....................................................................................................................................16 
 
Figure 6.  Diagram depicting a sample being sputtered by a beam of primary ions, resulting in 
the backscatter of secondary atoms, molecules, and ions (Recreated after Evans Analytical Group  
LLC, 2010).....................................................................................................................................18 
 
Figure 7.  Diagram depicting average zircon sample destruction area of SIMS, LA-ICPMS, 
and TIMS in cross-section view.  SIMS spot size is typically 10-20 ?m and <2 ?m depth.  LA-
ICPMS spot size is typically 30-60 ?m and 10-20 ?m depth.  TIMS analysis consumes the  
sample in its entirety (Recreated after Ko?ler & Sylvester, 2003)...................................................20 
 
Figure 8.  Isochron diagram illustrating both the two-point model isochron method (dashed line) 
and internal isochron for multiple spots on single crystals (solid line) (Schmitt, 2009).  A  
comparison with bulk TIMS data (Condomines, 1997) is also provided......................................23 
 
Figure 9.  A)  Schematic diagram of a sample holder showing the backing plate and spring. Note 
that the amount of mount surface area available for analysis is decreased by 0.2 inches after 
insertion into the sample holder (From UCLA, 2010).  B)  Photograph of a standard sample  
holder (From UCLA, 2010)...........................................................................................................28
viii 
 
Figure 10.  Final mount of Dayingshan zircons after having been pressed into indium and 
coated in a thin layer of gold.  Zircons were later numbered by a computer in the order in  
which they were sputtered................................................................................................................................29 
 
Figure 11.  Top - Photograph of the Cameca ims 1270 at the NSF National Ion Microprobe  
Facility at UCLA. Bottom - Author at control console of the Cameca ims 1270..........................31 
 
Figure 12.  3D schematic of CAMECA ims-1270 instrument and its components (From  
UCLA, 2011)..............................................................................................................................................................33 
 
Figure 13.  Diagram depicting the fundamental components of a SIMS instrument (Recreated  
after Stern, 2009)...........................................................................................................................51 
 
Figure 14.  FeO/MgO vs. SiO2 plot demonstrating an overall calc-alkaline trend in Dayingshan 
samples.  The dividing line is defined by Irvine and Barager (1971).  Data points were collected  
from Zou (2010), Wang, F. et al. (2006), and Zhao and Fan (2010).............................................55 
 
Figure 15.  REE plot of sample YTC9724-5 from Dayingshan and sample MA02 from Maanshan 
(Zou et al., 2010).  The vertical axis is normalized using average abundances in chondritic  
meteorites.  The negative slope indicates enrichment in LREE?s.................................................56 
 
Figure 16.  Spider diagram of Dayingshan (YTC9724-5) and Maanshan (MA02) (Zou et al., 
2010) trace elements.  The vertical axis is normalized using estimated primitive mantle.  A  
spiked, irregular pattern with an overall negative slope is indicative of a calc-alkaline sample...57 
 
Figure 17.  Cathodoluminescence images of sample Day-int4 and Day-int1 with SIMS crater  
spots.  Growth zoning is not well-developed in these zircons............................................................59 
 
Figure 18.  U/Th isochron plot for zircon cores from Dayingshan.  Chart was constructed and  
ages were determined using Isoplot (Ludwig, 2003).....................................................................61 
 
Figure 19.  Mixture modeling plot of zircon core ages from Dayingshan produced using the  
probability density function from Isoplot (Ludwig, 2003)............................................................63 
 
Figure 20.  U/Th isochron plot for zircon rims from Dayingshan using shallow depth profiling.   
Chart was constructed and ages were determined using Isoplot (Ludwig, 2003).........................65   
 
Figure 21.  Satellite image of the southern portion of the Tengchong volcanic field showing the 
distribution of some of the major cities and villages in the region.  Maanshan and Dayingshan are 
outlined in red.  Major cities and villages, including Tengchong (population 620,000), are  
outlined in yellow.  Map produced using Google Earth................................................................69
 
 
 
1 
 
INTRODUCTION 
  Volcanism in the Tibetan Plateau has been occurring throughout the Cenozoic 
since the development of the Himalayas.  The Tengchong volcanic field (TVF) (Fig. 1) is 
located in the southeastern portion of the Tibetan Plateau (24?40?-25?30?N, 98?15?-
98?45?E), and has recorded active volcanism from ~ 5 Ma to ~10 ka (Zhu et al., 1983; 
Zou et al., 2010).  Maanshan, Dayingshan, and Heikongshan are the three most recently 
active volcanoes in the TVF, each with recorded Holocene (<10 ka) eruptions.  These 
volcanoes are considered dormant, as they still have eruptive potential.  The volcanism is 
derived from a potassic melt, and is post-collisional, as the continental collision that 
developed the Himalayas initiated much earlier (~65 Ma).  There are numerous hot 
springs in the area, indicating active geothermal fields that show potential for volcanic 
eruptions (Zhiquan, 2005).  The origin of the potassic volcanism is ambiguous, and rocks 
appropriate for U-Th dating are rare in the Tibetan Plateau.     
 Young, Holocene volcanic rocks from the TVF contain zircon crystals suitable for 
U-Th disequilibrium studies (Zou et al., 2010).  Zircon analysis is a critical tool in the 
fields of geochemistry and geochronology due to its ability to incorporate and retain 
elemental and isotopic information.  This retained information is crucial for 
understanding the nature, origin and age of a particular rock.  Of particular interest is the 
ability of zircon to incorporate radioactive Uranium isotopes into its crystal structure.  
The incorporation of this isotope allows geologists to determine an absolute age of a rock 
sample through radiometric dating, which is done by measuring the amount of parent  
2 
 
 
Fig. 1.  Location map of the Tengchong volcanic field in SE China.  TVF lies in a N-S 
trending fault zone between the Sagaing and Red River faults, and lies ~200 km from the 
subduction-related Burma volcanic arc (After Zou et al., 2009). 
3 
 
isotopes (U) in relation to the amount of daughter isotopes (Pb or Th) into which the 
parent decays.  While zircon is most widely known for its uses in dating ancient rocks by 
the 238U-206Pb method, it is also becoming an essential tool in Quaternary geochronology 
through the 238U-230Th method.  This is because zircons are enriched in U and have a 
large spread in U/Th ratios, and allow for the recording of the pre-eruptive history of a 
magma up to 350 ka.  This is especially useful for determining the storage time of magma 
within a magma chamber.  With the aid of micrometer-scale spatial resolution and high 
sensitivity provided by secondary ion mass spectrometry (SIMS), a radiometric dating 
technique that measures the composition of solid materials, individual crystallization 
events can be recorded from analysis of zircon crystals.
4 
 
OBJECTIVES 
 This research attempts to better constrain magma chamber storage time prior to 
eruption by analysis of samples from the Dayingshan volcano in the Tengchong volcanic 
field.  Of the three recently active volcanoes, Dayingshan was chosen because it has not 
been previously studied in this regard and has a rich abundance of zircon.  Better 
constraints can be put on magma storage time and magma source generation by zircon 
and whole-rock analysis.  Studies regarding magma storage time are relatively new to the 
field of geochronology.  This research will also demonstrate the capabilities of SIMS 
dating techniques on Quaternary samples.          
 The objectives of this study are as follows:  (1) to determine the age(s) of zircon 
crystallization events from Dayingshan volcanic rocks using zircon U-Th dating methods 
and SIMS; (2) to utilize this data to determine how long magma is stored in the magma 
chamber before an eruption in this unique volcanic environment; and (3) to potentially 
determine the source of the volcanism through whole-rock major and trace element 
analysis. 
5 
 
BACKGROUND 
Geologic Setting 
 The formation of the southwestern region of China is controversial in large part 
due to its structural complexities.  Fan (1978) separated southwestern China into five 
major tectonic units and briefly summarized a likely history of tectonic evolution.  The 
major tectonic events are a collision between the Chinese (Amurian) and Eurasian plates 
in the Late Triassic, a collisional event between the Tibetan block (Cimmerian terranes?) 
and Chinese plate, and a final collision between the Indian and Eurasian plates in the Late 
Cretaceous.  Fan (1978) theorized that the Quaternary volcanics in Tengchong likely 
represent the easternmost edge of the Indian plate; however, more recent geophysical and 
seismic data (Wang & Long, 1998; Lei et al., 2009) indicate Indian plate subduction does 
not reach this far East.  Possible rotation and extrusion due to the ongoing collision 
further complicates the heavily faulted region (Tapponnier et al., 1982).    
 The Tengchong volcanic field is located along the southeastern margin of the 
Tibetan plateau in the Yunnan province of China.  The field is in close proximity to the 
border of China and Burma, and sits ~450 km from the Indian plate.  The field lies in a 
structurally complex area due to several faults and suture zones that run through and 
intersect in the area.  The Sagaing dextral fault, Myitkyina suture zone, and Burma 
gneissic belt lie west of the field, while the Gaoligong metamorphic belt and Red River 
fault zone lie to the east.  This has created a N-S fault zone in which the field is situated.  
6 
 
Most of these faults formed as a result of the continental collision between India and 
Asia.  Further to the West is the Burma volcanic arc, which is almost certainly a 
continental arc developed by shallow continental subduction and melting of the Indo-
Australian plate.  Volcanism has also been active since the late Tertiary, beginning long 
after the collision initiated between the Indo-Australian and Eurasian plate (~65 Ma).  
The field is unique in that it is the only active volcanic zone in the region, as recent 
geothermal studies suggest that a magmatic reservoir is still present beneath the field (Bai 
et al., 2002).    
  Older periods of volcanism are evident in the northern and southern parts of the 
field, while more recent eruptions have migrated to the central part (Wang, F. et al., 
2006).  Mu et al. (1987), Ji (1998), and Li et al. (2000) divide eruptions in the area into 
four major stages:  late Miocene-Pliocene basalt and olivine-basalt volcanic rocks (5.5-
4.0 and 3.8-0.9 Ma), Pleistocene andesites and dacites (0.8-0.1 Ma), and late Pleistocene-
Holocene basalts and basaltic andesites (0.1-0.01 Ma).  Table 1 lists these stages and 
some important characteristics of each.  While the field is composed of dominantly 
basaltic rock, more andesitic rock types are associated with the three youngest volcanoes.  
Rocks associated with this recent volcanism also contain high abundances of potassium.  
Wang, Y. et al. (2006) reported a 1.5 to 3.65% increase in K2O content from the Pliocene 
to Holocene.  Volcanic rocks in the area typically contain high abundances of Al2O3 and 
K2O and low abundances of TiO2 and light rare earth elements (LREE) (Wang, Y. et al., 
2006).  The field?s location in a N-S trending fault zone has led to the eastern and western 
parts of the area being uplifted while the central region has been depressed, creating  
7 
 
 
 
 
 
 
 
 
Table 1 
The four stages of Tengchong volcanism and some characteristics.  Distribution data is from Zhu et al. (1983).  With the 
exception of stage 3, there is an increasing trend in K2O and SiO2 content through time (Zhu et al., 1983).  Ages were 
determined based on unpublished K-Ar dates by Zhu et al. (1983). 
 
S t a g e  o f  V o l c a n i sm Age D o m i n a n t  r o c k  t y p e D i st r i b u t i o n  w i t h i n  f i e l d
1 l a t e  M i o c e n e - P l i o c e n e b a s a l t s o u t h e a s t
( 5 . 5  -  4  M a )
2 l a t e  P l i o c e n e - P l e i s t o c e n e o l i v i n e  b a s a l t n o r t h  a n d  s o u t h
( 3 . 8 - 0 . 9  M a )
3 P l e i s t o c e n e a n d e s i t e / d a c i t e n o r t h  a n d  s o u t h w e s t
( 0 . 8 - 0 . 1  M a )
4 l a t e  P l e i s t o c e n e - H o l o c e n e b a s a l t / b a s a l t i c  a n d e s i t e n o r t h  a n d  w e s t
( 0 . 1 - 0 . 0 1  M a )
8 
 
elevation differences of more than 500 m (Wang, Y. et al., 2006).  Total crustal thickness 
in the region is 40-50 km (Zhu et al., 1983).    
The formation of the three most recently active volcanoes, Heikongshan, 
Dayingshan, and Maanshan, is poorly understood.  Some believe the melts contain a 
continental crust component, and are thus generated from subduction and/or wall rock 
assimilation (Mu et al., 1987; Zhu et al., 1983).  Others interpret recent volcanism to be 
the result of a heterogenous mantle source that incorporates no crustal material at all 
(Cong et al., 1994).  Wang, F. et al. (2006) suggest that both of these sources are likely 
responsible for generating the lavas.  It is probable that there are several different factors 
contributing to the melt generation and periodic volcanism.  Figure 2 is a diagram 
showing the distribution and relative ages of the three most recently active volcanoes and 
surrounding rocks.       
 This study focuses on Dayingshan volcano, the largest of the three active 
volcanoes in the Tengchong volcanic field.  Several episodes of erupted lavas and a large 
scoria cone make up the volcano, with the most recent rocks consisting of vesicular 
basaltic andesite.  The mineral constituents of the rock are plagioclase and olivine 
phenocrysts (~10-15%) in a matrix consisting mostly of plagioclase, olivine, augite, and 
volcanic glass (Fig. 3).  A younger lava cone with a lava pool has developed and 
currently sits beside the primary cone (Wei et al., 2002).  Figure 4 shows the distribution 
of the depositional units erupted from Dayingshan.  Rock samples from Dayingshan can 
be dated due to a relative abundance of the mineral zircon. 
 
 
 
 
9 
 
 
 
 
 
 
 
Fig. 2.  Distribution and relative ages of the three most recently active volcanoes and 
surrounding rocks.  Most volcanoes represented are small cinder cones (Modified from 
Zou et al., 2009). 
 
 
 
10 
 
 
 
 
 
 
Fig. 3.  Photomicrographs of Dayingshan basaltic andesite.  A) 4X view showing 
large phenocrysts of olivine (middle center) and plagioclase (bottom center).  B) 
10X view of the groundmass showing dominantly plagioclase laths in a dark matrix.   
 
A 
B 
11 
 
 
 
 
 
 
 
 
 
 
Fig. 4.  Distribution of depositional units deposited by multiple eruptive events from 
Dayingshan volcano.  I is the oldest flow, and V is the youngest.  A small lava lake has 
developed to the northwest of the scoria cone (From Wei et al., 2002).   
  
 
 
 
 
 
12 
 
Concerning Zircon 
 Zircon (ZrSiO4) is a common accessory mineral that forms in rocks all over the 
world.  Zircon crystals can be found in sedimentary, metamorphic, and igneous rocks, 
and are mostly known for their importance to geochronology and crustal evolution 
studies.  The most important reason zircons are useful in geochronology is because they 
typically contain radioactive uranium, often leading to metamictization of the mineral, 
and they incorporate very little lead.  Radioactive elements such as uranium retain 
information that is critical for understanding the nature, origin, and age of a particular 
rock.  Zircon has a strong, tetragonal, prismatic crystal structure and a hardness of 7.5 
(Perkins, 2002), which contributes to the extreme durability of the mineral.  In fact, 
zircons are so resilient to weathering that they have been found in terrestrial Earth 
samples to be as old as 4.404 ? 9 Ga (Wilde, 2001).  Zircons are also stable in 
temperatures up to 1690?C and pressures up to 4.8 GPa (Finch & Hanchar, 2003).  This 
stability in extreme temperatures and pressures allows zircon minerals to endure most 
metamorphic processes without changing the composition.     
 This research focuses on the occurrence of zircon in fresh igneous rocks.  Unlike 
dating zircon from detrital or metamorphic rock, the dating of zircon in an igneous rock 
yields the age at which the rock cooled from a melt.  The volcanic rocks produced at 
Dayingshan are fairly silica-rich, which is an important factor in zircon production.  
Zircons are most common in igneous rocks of intermediate to Si-saturated composition 
and least common in less Si-saturated rocks, such as basalts (Hoskin & Schaltegger, 
2003).  Zircons in extrusive volcanic rocks tend to crystallize rapidly, resulting in 
relatively small crystals that typically show an acicular habit, with length to width ratios 
13 
 
up to 1:12 (Hoskin & Schaltegger, 2003).  A common texture seen in igneous zircons is 
growth zoning.  Zoning records different crystallization events throughout the life of the 
zircon, recording and preserving thermal events from tens to millions of years.  With the 
development of mass spectrometry, geologists can obtain the approximate ages of these 
different crystallization events.   
 The current study attempts to use zircon to investigate igneous processes such as 
magma chamber storage time and the use of zircon as a possible provenance-indicator.  
Zircons must be extracted from the source rock and dated in order to attain their early 
pre-eruptive crystallization age, which corresponds with early magma chamber evolution.  
In intermediate to felsic magmas, zircons will typically crystallize and remain suspended 
in a melt for time periods greater than 100 ka (Simon et al., 2008).  When a melt rises 
from great depth and reaches the magma chamber, it begins to cool.  At temperatures of 
~800?C, zircons dissolve fairly rapidly into a hydrous melt (Reid et al., 1997).  Therefore, 
the ages obtained from the zircons reflect the last time the melt cooled through this 
temperature.  Consequently, it can be concluded that zircon crystallization ages date the 
cooling of magma to its zircon saturation temperature, which can be determined based on 
U-Th disequilibrium measurements (Reid et al., 1997).  Magma storage time can thus be 
discerned by subtracting the age of the last eruption event from the age of the zircons in 
the sample rock; however, it must first be determined that the zircons grew in the magma 
body during the build-up to eruption.  Because the ability to resolve age differences 
decreases with rock age, the most informative data about residence time scales come 
from young eruptions (Simon et al., 2008).   
14 
 
Using zircons to determine magma provenance is more complicated.  In order to 
do so, one must relate the atomic composition of zircon to lithology.  Several studies 
have had moderate success, such as Heaman et al. (1990), who used plots of Lu, Sc, Th/U 
and Lu/Sm versus Hf to relate zircons to several specific environments, and Hoskin & 
Ireland (2000), who studied the rare earth element (REE) abundance differences in 
zircons from mantle-derived rock and compared those with crustal zircons.  The 
relationship between certain REE abundances and their derivation from a crustal or 
mantle source provides strong evidence for the origins of the melt.  Ultimately, there is 
no clear, defining relationship between igneous zircon composition and magmatic source.  
For whole-rock U-series data, pronounced 230Th excesses in young (< 350 ka) volcanic 
rocks may indicate the lavas were produced from a deep mantle source (Zou & Fan, 
2010).  On the other hand, 238U excesses are attributed to the addition of fluids from the 
subducting plate into the mantle wedge (i.e. subduction zones) or shallow mantle melting 
of a spinel peridotite source. 
 
Uranium-Series Radiometric Dating 
 Radiometric dating works on the principle that radioactive parent isotopes decay 
at constant rates through time into daughter isotopes.  While the decay of one particular 
isotope is spontaneous, probability dictates that a large population of isotopes decay at 
regular rates known as half-lives.  The half-life of a decay pair is the time it takes for half 
of the parent isotopes to decay into stable daughter isotopes.  The rate of decay depends 
only on the properties of the isotope, and is not affected by environmental factors such as 
temperature and pressure.  This constant rate of decay allows for the parent-daughter ratio 
15 
 
to be used as a clock to measure the time that has elapsed since the crystal formed.  An 
assumption must be made that the crystal has a closed system to temperature and 
pressure.  Because alteration can sometimes be detected through geologic evidence or 
growth zoning, and using more than one parent-daughter system can commonly be used 
to cross-check ages, this assumption can often be made confidently.  The resilience of 
zircon to alteration due to environmental changes also provides confidence in this 
assumption.  Some minerals may incorporate daughter isotopes into the original 
composition.  In this case, an isochron method must be applied to attain crystal age. 
 Uranium-series dating is the most commonly used isotopic series in radiometric 
dating for several reasons.  The first is that it has several intermediate isotopes with a 
range of half-lives before it reaches its final decay product of Pb, providing several useful 
time frames for dating.  For example, 238U-230Th has a half-life of 75,690 years, while 
238U-206Pb has a half-life of 4.5 billion years.  Because most accessory minerals 
incorporate little to no lead, ages based on the latter decay pair are widely accepted.  
Figure 5 follows the 238U parent isotope and its decay into several intermediate daughter 
isotopes. 
 Radiometric dating assumes a closed system.  Although a closed system 
assumption is sometimes contested, it is widely accepted for zircon U-series dating 
because elements are immobile in zircon even at magmatic temperatures (Schmitt, 2009).  
This closed system can be disturbed by partial melting, and the reader is referred to the 
book, Quantitative Geochemistry, by Zou (2009) for models that relate the extents of U-
series decay to the melting process as it pertains to elemental partition coefficients, 
melting porosity, melting rate, and melting time. 
16 
 
  
 
 
 
  
Fig. 5.  238U decay chain depicting either alpha or beta decay into several intermediate 
isotopes before the final stable 206Pb isotope is reached.  N = atomic number;  Z = atomic 
mass (From Berg, 2008).  
 
 
 
 
 
 
 
 
17 
 
 While several uranium decay series may be used to radiometrically date zircons, 
the most proficient and well-known are the two U-Pb series due to long half-lives. 
Another reason for the wide use of zircon U-series dating is that it has two clocks.  
Essentially, the decay of both the 238U and 235U isotope allow for the ability to cross-
check and confirm age data.  Other commonly used U-series decay pairs in geology are 
U-Th, Th-Ra and U-Pa.  Because Dayingshan volcanic rocks are geologically young, the 
238U-230Th decay pair is most appropriate.  The half-life of the 238U-230Th decay pair is 
75,690 yrs, which results in a maximum attainable age of ~350 ka (Schmitt, 2009).  Mass 
spectrometry can be used to measure the approximate parent to daughter ratios of 238U-
230Th.  Because 230Th abundances are especially low in upper Quaternary rocks, an 
instrument with low background noise and high sensitivity is ideal. 
 
Secondary Ion Mass Spectrometry (SIMS) 
 SIMS is a radiometric dating technique that measures the composition of solid 
materials on a micron scale, and is most commonly performed with an ion microprobe. 
SIMS main strengths are in trace element quantification due to low backgrounds and high 
sensitivity (Stern, 2009).  The target zircon is initially sputtered with a high-energy beam 
of primary oxygen ions (16O2- or 16O-) that causes some of the atoms and molecules of the 
zircon to become ionized (Fig. 6). The secondary ions, which have been sputtered off the 
target zircon and thus represent the zircon composition, are separated by a mass 
spectrometer and counted by secondary ion detectors (Ireland and Williams, 2003).    
   
 
18 
 
 
 
 
 
 
  
Fig. 6.  Diagram depicting a sample being sputtered by a beam of primary ions, resulting 
in the backscatter of secondary atoms, molecules, and ions (After Evans Analytical 
Group LLC, 2010). 
  
 
 
 
 
 
 
19 
 
 Erroneous data may be recorded from SIMS due to any number of different 
instrumental and sample preparation errors, which will be discussed in greater detail 
below.  To make certain these errors are not occurring, multiple zircon standards (e.g., 
AS-3 from the Duluth anorthosites) are mounted along with the unknown zircon samples.  
Standards are zircons from rocks of a known age.  By using SIMS on these standards, one 
can determine if there is an error in the machine and make the necessary adjustments to 
correct the error.  Zircon standards are especially necessary to correct for mass 
discrimination of U, Th, and Pb. 
 SIMS is the least destructive of the radiometric dating techniques, creating a 
crater 10-50 ?m in diameter with an approximate depth of < 5 ?m (Ireland & Williams, 
2003).  Amount of sample destruction is much less than comparable dating techniques 
such as Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) and 
Thermal Ionization Mass Spectrometry (TIMS) (Fig. 7).  There is also very little heating 
and vaporization due to a much lower amount of energy absorbed by the target (Stern, 
2009).  SIMS high spatial resolution allows for the targeting of specific growth zones on 
the zircon crystal.   
The use of SIMS in Quaternary-age materials is a relatively new approach in the 
field of geochronology.  High sensitivity and micrometer-scale spatial resolution make 
SIMS a premier tool in Quaternary geochronology, as the useful yield of U-series 
isotopes is typically low in rocks so young.  SIMS, coupled with imaging techniques such 
as backscattered electron (BSE) imaging and cathodoluminescence (CL), allows the user 
to finely target specific regions on a crystal surface for chemical and isotopic analysis 
(Ireland & Williams, 2003).  Depth profiling, another SIMS technique, enhances the  
20 
 
 
 
 
 
 
 
                                     
 
Fig. 7.  Diagram depicting average zircon sample destruction area of SIMS, LA-
ICPMS, and TIMS in cross-section view.  SIMS spot size is typically 10-20 ?m and <2 
?m depth.  LA-ICPMS spot size is typically 30-60 ?m and 10-20 ?m depth.  TIMS 
analysis consumes the sample in its entirety (After Ko?ler & Sylvester, 2003). 
 
 
 
 
 
 
 
 
21 
 
spatial resolution to several micrometers, which also aids in obtaining crystallization ages 
in zoned zircons. 
 An isochron method must be applied in order to ultimately attain rock age due to 
the fact that zircon may initially incorporate 230Th into the system.  An isochron is a 
straight line plotted on a Dr/Dn versus P/Dn diagram.  This method works on the 
assumption that the ratio of a radiogenic daughter isotope (Dr), formed by the decay of a 
parent isotope (P), to a related nonradiogenic isotope (Dn) was initially the same for each 
zircon analyzed.  The age is ultimately attained by measuring the slope of the isochron, 
which increases with age.  The isochron method is useful because it determines the initial 
amount of radiogenic daughter isotopes; therefore, no assumptions of the initial amount 
of daughter isotopes need be made.  For zircons from Dayingshan, an isochron is plotted 
on a (230Th)/(232Th) vs. (238U)/(232Th) diagram.  One can develop an isochron in two 
ways: (1) by using the two-point model isochron method using zircon melt-pairs, or (2) 
by using internal isochrons for multiple spots on single or multiple crystals (Schmitt, 
2009).  The following equation is used to construct an isochron (? = decay constant; t = 
time between radioactive disequilibrium generation event and current measurement): 
 
 
 
The age can then be calculated from the slope (m) of that line using the following 
equation: 
     
22 
 
 Figure 8 is an isochron diagram of zircons collected from Puy de Dome, a large 
lava dome in south-central France, illustrating both the two-point model isochron method 
and an internal isochron for multiple spots on single crystals (Schmitt, 2009).  The two-
point model isochron method using zircon-melt pairs is used if uranium-series isotope 
abundances are too low.  For Dayingshan zircons, the internal isochron method is 
applied; however, because of the small size of the zircons, isochrons are determined 
based on single spots on multiple crystals.   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
23 
 
 
 
 
 
 
 
 
Fig. 8.  Isochron diagram illustrating both the two-point model isochron method (dashed 
line) and internal isochron for multiple spots on single crystals (solid line) (From Schmitt, 
2009).  A comparison with bulk TIMS data (Condomines, 1997) is also provided. 
 
 
 
 
 
 
 
24 
 
PREVIOUS WORK 
 Some of the first isotopic and geochemical work done in the Tengchong volcanic 
field was performed by Zhu et al. (1983).  They recognized that the compositions of the 
volcanic rocks in the area were complex and changed over time.  The wide range of 
volcanic compositions were observed and separated into five groups belonging to three 
series:  a major series (high-Al basalts), an andesite-dacite series, and a high-Mg series.  
Isotopic analysis indicated an enriched mantle source attributed to older subducted 
components (subduction prior to Indian-Eurasian plate collision).  The same authors also 
noted that the most recent volcanics seemed closely linked to the tectonic environment.  
Periods of extensional regimes are marked by more frequent eruptions, while periods of 
compressional regimes are marked by pauses in volcanic activity. 
 Wang, Y. et al. (2006) expanded on tectonics as the controlling factor for volcanic 
activity.  Based on the timing of faulting and basin formation, analysis of the cooling 
history of the mountain belt, and calculations of seismic foci, they concluded that the 
magma formed as a result of collisional orogenic processes, but strike-slip motion of the 
Saigang fault is the biggest factor that controls volcanic eruptions.  
 Wang, F. et al. (2006) noted enriched mantle characteristics in the Tengchong 
volcanic rocks, and concluded that the enrichment was due to partial melting of a 
metasomatized mantle source.  Wang, F. et al. (2006) were also the first to measure U 
and Th isotopes in the Tengchong volcanic field, and determined from these 
measurements that there was probably some heterogeneity in the source.  They concluded
25 
 
that there are two possible source domains for the lava; (1) an LREE-enriched, high 
Rb/Sr end-member, and (2) a second end-member representing a more typical arc-type 
melt.  Another important focus in this study was the authors attempt to put constraints on 
magma chamber storage time.  This was done based on U-Th and 40Ar/39Ar age dating, 
but results were inconclusive as different ages (~77 ka for U-Th; ~32.2 ka for 40Ar/39Ar) 
were calculated from the same crystal using these two techniques.  Wang, F. et al. (2006) 
only worked on major minerals, and these rock-forming minerals have relatively low U 
and Th concentrations.  Their data is therefore subject to high errors and inconsistencies.            
 Zou et al. (2010) focused more on the times scales and nature of magma storage, 
using U-Th dating of zircons from Maanshan volcano to calculate magma storage time.  
Unlike Wang, F. et al. (2006), Zou et al. (2010) were able to separate measured zircons 
into two populations by utilizing SIMS.  A magma storage time of 45 ka was determined 
for the most recent eruption.  Due to bi-modal zircon ages, it was concluded that the older 
age population (~91 ka) represented remobilized zircon antecrysts from an earlier phase 
of magmatism, while the younger population (~55 ka) grew in the magma body itself 
prior to eruption.  The study also concluded based on zircon saturation calculations that 
there are no inherited zircons from country rocks in the most recent lava flows.   
26 
 
METHODS 
Zircon Extraction 
 The initial stage in this research was to extract zircon crystals from a volcanic 
rock sample from Dayingshan (sample # TC09026).  The first step in the zircon 
extraction process is to crush and grind the rock into particles approximately 25-50 ?m in 
diameter.  This was the approximate particle size at which the rock became 
disaggregated.  Crushing was done using a rock hammer and laboratory disc mill.  The 
rock hammer was used to break the rock into pieces small enough to feed into the disc 
mill, which then ground the rock into smaller (~25-50 ?m) particles.  While breaking the 
rock with a rock hammer, a box was used to contain the broken rock fragments.  The 
ceramic laboratory disc mill used to grind the sample further was brand new, and thus 
contained no contaminants.  After grinding to the appropriate size, the sample was then 
decanted with water to separate some of the lighter minerals from the heavier minerals.  
Minerals that remained in suspension in the water were poured off (e.g., mica), while the 
denser minerals, such as zircon, sank in the water.  A high-powered hand magnet was 
then repeatedly used to draw off metallic minerals.   
 The next step is heavy liquid separation, which is used to separate out only the 
heaviest minerals (e.g. zircon).  The heavy liquid separation process was done using the 
facilities and equipment of Columbus State University.  The heavy liquid used was 
methylene iodide (MEI).  MEI (CH2I2) is a good liquid to use because it has a relatively 
high specific gravity of 3.335.  Because zircon has a specific gravity of 4.68 (Perkins, 
27 
 
2002), zircon sinks in the MEI while lighter minerals float to the top.  After mixing a 
small amount of the rock sample into the MEI in a separatory funnel, a 24-hour time 
period was allowed to elapse, giving the heavy minerals sufficient time to sink through 
the heavy liquid.  After 24 hours, the MEI at the bottom of the separatory funnel, which 
held the heaviest minerals, was poured out onto filter paper.  The sample was then 
washed in acetone and dried in an oven in order to drive off the last remaining MEI.   
 The last step in the zircon extraction process was to pick out the zircons from the 
other heavy minerals separated out by the heavy liquid.  This was carefully and 
meticulously done using a fine-point needle under an optical microscope.  The entire 
process was repeated several times over the course of two weeks until a sufficient number 
of zircons were recovered (~30).          
 
Sample Preparation 
After the separation process, the zircons must be prepared and mounted specifically for 
SIMS.  Proper sample preparation is of the utmost importance for SIMS.  Secondary ion 
yields are sensitive to local topographic and electrostatic features of the sample mount 
(Stern, 2009).  The crystals are first embedded in indium, washed in dilute HCl, and 
plated with a thin (20-40 nm) gold layer to generate a conducting sample surface (Fig. 9).  
Indium is a soft metal that is used instead of traditional epoxy to minimize potential 
interferences on 230Th isotopes from the matrix.  The unpolished mount is then placed in 
a sample holder, the standard dimensions of which are ~ 1 inch in diameter with a 
thickness of ~1/2 cm (Schmitt, 2009).  A nonmagnetic spring and backing plate hold the 
sample in place (Fig. 10).  The sample is unpolished because unpolished zircons allow for  
28 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 9.  Final mount of Dayingshan zircons after having been pressed into indium 
and coated in a thin layer of gold.  Zircons were later numbered by a computer in the 
order in which they were sputtered.     
29 
 
 
 
 
 
 
 
 
 
Fig. 10.  A.) Schematic diagram of a sample holder showing the backing plate and spring. 
Note that the amount of mount surface area available for analysis is decreased by 0.2 
inches after insertion into the sample holder. B.) Photograph of a standard sample holder 
(From UCLA, 2010).   
 
 
 
 
 
 
 
 
 
30 
 
shallow depth profiling which provides enhanced spatial resolution on natural crystal 
surfaces. After the mount is inserted into the sample holder, the sample holder must be 
inserted into the instrument through an airlock system as the ion probe is kept under Ultra 
High Vacuum (UHV).  The sample was then sputtered with a primary beam of 16O- ions 
generated in the duoplasmatron in order to obtain rim ages.  The duoplasmatron works by 
converting gas into an ion beam.  Zircon sputter rates are ~0.05 ?m3/nA/sec (Schmitt, 
2003), and the typical time required to sputter one zircon is ~20 minutes.   
After sputtering the unpolished zircons, the sample was then removed from the 
machine, polished using a diamond polishing compound, cleaned with dilute HCl, and 
coated with another thin Au layer.  Zircons were then sputtered again to obtain core ages.  
Because a relatively flat crystal face is needed in order to accommodate the ion beam, it 
is important to note that fewer zircons were measured during the unpolished 
measurements due to a smaller percentage of zircon surface area.  The zircons initially 
pressed into the Indium may or may not yield a flat crystal surface for measuring.  Upon 
completion, the final zircon mount, containing the polished zircons with SIMS craters, 
was kept for potential future analysis.  
 
Cameca ims 1270 Analytical Methods 
 Measurements for this research were done using the Cameca ims 1270 at the NSF 
National Ion Microprobe Facility at the University of California, Los Angeles (UCLA) 
(Fig. 11).  The facility was commissioned as a national facility in 1996, and scientists 
have generated over 300 publications using UCLA SIMS data (UCLA, 2011). 230Th/232Th 
and 238U/232Th analyses with the Cameca ims 1270 achieves an average precision of  
31 
 
 
Fig. 11.  Top - Photograph of the Cameca ims 1270 at the NSF National Ion 
Microprobe Facility at UCLA. Bottom - Author at control console of the Cameca 
ims 1270. 
 
32 
 
~1-2 % (Zou et al., 2010).  230Th/232Th and 238U/232Th analyses with the Cameca ims 
1270 achieves an average precision of ~1-2 % (Zou et al., 2010).  There are several SIMS 
instruments and analytical approaches; however this paper will only address the 
operational procedures for the Cameca ims 1270.  Techniques for other SIMS 
instruments may vary, and the reader is referred to Ireland & Williams (2003) for 
operation and techniques of some of these other instruments (i.e. SHRIMP I and 
SHRIMP II). Figure 12 represents a 3D schematic of the Cameca ims 1270. 
 The most important secondary ion intensities measured by SIMS U-Th dating are 
230Th16O+, 232Th16O+, and 238U16O+.  Oxides are measured because they typically show 
higher intensities than metals.  Ultimately, the counts of these three oxides are used to 
calculate the age of the crystal.  90Zr216O4+ is also measured as a reference.  These ions 
are measured both individually and against background measurements, and are gain 
corrected to ensure accurate counts and calibration.  The raw data for measured 
Dayingshan zircons are presented in Table 2.  AS-3 zircons from the Duluth Complex 
were used as standards to calibrate the relative sensitivities for 238UO, 232ThO and 
230ThO.  Radiogenic 206Pb/208Pb is measured in the AS-3 zircons rather than Th/U 
because in old, concordant zircons with known ages, the radiogenic 208Pb/206Pb is a 
unique function of the Th/U atomic ratio (Zou et al., 2010); therefore, a Th/U relative 
sensitivity factor can be calculated.  The primary current was generated at ~40-80 nA, 
and the secondary ions were analyzed at a mass resolving power of ~5000.  
 SIMS works by sputtering the target sample with a primary beam of either 16O2- 
or 16O- ions.  This beam is generated using a duoplasmatron, which converts the gas into  
33 
 
 
Fig. 12.  3D schematic of CAMECA ims-1270 instrument and its components (From UCLA, 2011). 
34 
 
 
Table 2   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively. 
 
S a m pl e 2 4 6 . 0 2 8 0 4 / 2 4 6 . 0 2 8 0 4 / U  O / U  O / 2 4 6 . 0 2 8 0 4 / 2 4 6 . 0 2 8 0 4 /
U  O U  O Th  O Th  O Th  O Th  O
1  s.e . 1  s.e . 1  s.e .
D a y _ r i m_ z @ 1 1 . 2 9 E - 0 5 7 . 3 1 E - 0 7 1 . 5 6 E + 0 0 5 . 5 4 E - 0 3 2 . 0 1 E - 0 5 1 . 0 7 E - 0 6
D a y _ r i m_ z @ 2 1 . 0 8 E - 0 5 3 . 1 2 E - 0 7 5 . 5 2 E - 0 1 1 . 0 3 E - 0 2 5 . 9 5 E - 0 6 1 . 8 1 E - 0 7
D a y _ r i m_ z @ 3 1 . 0 6 E - 0 5 4 . 1 9 E - 0 7 6 . 5 5 E - 0 1 6 . 1 5 E - 0 3 6 . 9 6 E - 0 6 2 . 7 4 E - 0 7
D a y _ r i m_ z @ 4 1 . 2 1 E - 0 5 5 . 8 7 E - 0 7 8 . 4 5 E - 0 1 5 . 4 7 E - 0 3 1 . 0 2 E - 0 5 4 . 8 4 E - 0 7
D a y _ r i m_ z @ 5 7 . 9 8 E - 0 6 2 . 5 5 E - 0 7 1 . 1 1 E + 0 0 1 . 8 6 E - 0 2 8 . 8 4 E - 0 6 2 . 8 2 E - 0 7
D a y _ r i m_ z @ 6 1 . 0 3 E - 0 5 2 . 9 9 E - 0 7 5 . 9 2 E - 0 1 2 . 3 8 E - 0 3 6 . 1 2 E - 0 6 1 . 7 7 E - 0 7
D a y _ r i m_ z @ 7 1 . 4 4 E - 0 5 7 . 7 2 E - 0 7 3 . 0 8 E - 0 1 4 . 3 0 E - 0 3 4 . 4 5 E - 0 6 2 . 6 6 E - 0 7
D a y _ r i m_ z @ 8 1 . 0 4 E - 0 5 3 . 5 1 E - 0 7 6 . 2 3 E - 0 1 1 . 9 3 E - 0 2 6 . 4 5 E - 0 6 2 . 5 0 E - 0 7
D a y _ r i m_ z @ 9 1 . 1 6 E - 0 5 3 . 5 0 E - 0 7 4 . 9 4 E - 0 1 3 . 0 6 E - 0 3 5 . 7 2 E - 0 6 1 . 7 3 E - 0 7
D a y _ r i m_ z @ 1 0 9 . 2 4 E - 0 6 3 . 4 9 E - 0 7 8 . 3 3 E - 0 1 1 . 3 5 E - 0 2 7 . 7 1 E - 0 6 3 . 2 8 E - 0 7
D a y _ r i m_ z @ 1 1 1 . 0 2 E - 0 5 3 . 6 1 E - 0 7 9 . 7 6 E - 0 1 9 . 0 8 E - 0 3 9 . 9 5 E - 0 6 3 . 5 3 E - 0 7
D a y _ r i m_ z @ 1 2 1 . 0 2 E - 0 5 2 . 6 1 E - 0 7 7 . 6 9 E - 0 1 3 . 3 6 E - 0 3 7 . 8 1 E - 0 6 1 . 9 1 E - 0 7
D a y _ r i m_ z @ 1 3 8 . 6 2 E - 0 6 2 . 4 6 E - 0 7 9 . 1 2 E - 0 1 6 . 7 8 E - 0 3 7 . 8 4 E - 0 6 2 . 1 0 E - 0 7
D a y _ r i m_ z @ 1 4 1 . 0 6 E - 0 5 3 . 6 8 E - 0 7 7 . 2 1 E - 0 1 3 . 7 5 E - 0 3 7 . 6 5 E - 0 6 2 . 6 6 E - 0 7
D a y _ r i m_ z @ 1 5 1 . 0 8 E - 0 5 4 . 5 0 E - 0 7 6 . 3 0 E - 0 1 1 . 1 7 E - 0 2 6 . 7 8 E - 0 6 3 . 0 5 E - 0 7
D a y _ r i m_ z @ 1 6 1 . 1 1 E - 0 5 5 . 2 0 E - 0 7 9 . 3 7 E - 0 1 7 . 1 2 E - 0 3 1 . 0 4 E - 0 5 4 . 8 6 E - 0 7
D a y _ r i m_ z @ 1 7 1 . 0 8 E - 0 5 3 . 3 6 E - 0 7 5 . 0 3 E - 0 1 3 . 4 1 E - 0 3 5 . 4 5 E - 0 6 1 . 7 3 E - 0 7
 
 
 
35 
 
 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively.   
 
S a m pl e 2 4 6 . 3 / 2 4 6 . 3 / 2 4 6 . 3 / 2 4 6 . 3 / 2 4 4 . 0 3 8 1 / 2 4 4 . 0 3 8 1 /
U  O U  O Th  O Th  O U  O U  O
1  s.e . 1  s.e . 1  s.e .
D a y _ r i m_ z @ 1 2 . 3 9 E - 0 7 7 . 8 5 E - 0 8 3 . 7 5 E - 0 7 1 . 2 3 E - 0 7 2 . 4 3 E - 0 6 3 . 2 0 E - 0 7
D a y _ r i m_ z @ 2 4 . 6 4 E - 0 7 1 . 5 9 E - 0 7 2 . 5 5 E - 0 7 8 . 5 2 E - 0 8 7 . 0 6 E - 0 7 8 . 0 7 E - 0 8
D a y _ r i m_ z @ 3 5 . 2 9 E - 0 7 3 . 3 6 E - 0 7 3 . 3 3 E - 0 7 2 . 0 7 E - 0 7 6 . 3 8 E - 0 7 1 . 0 8 E - 0 7
D a y _ r i m_ z @ 4 1 . 0 6 E - 0 6 5 . 3 8 E - 0 7 9 . 1 7 E - 0 7 4 . 6 9 E - 0 7 2 . 5 9 E - 0 6 3 . 7 5 E - 0 7
D a y _ r i m_ z @ 5 1 . 3 4 E - 0 7 6 . 7 7 E - 0 8 1 . 5 1 E - 0 7 7 . 6 6 E - 0 8 3 . 5 5 E - 0 7 5 . 3 8 E - 0 8
D a y _ r i m_ z @ 6 3 . 3 5 E - 0 7 1 . 3 5 E - 0 7 1 . 9 7 E - 0 7 8 . 0 2 E - 0 8 7 . 9 9 E - 0 7 8 . 1 8 E - 0 8
D a y _ r i m_ z @ 7 1 . 1 7 E - 0 6 4 . 0 5 E - 0 7 3 . 5 0 E - 0 7 1 . 2 1 E - 0 7 1 . 2 7 E - 0 6 1 . 8 4 E - 0 7
D a y _ r i m_ z @ 8 6 . 0 3 E - 0 7 3 . 8 7 E - 0 7 3 . 3 7 E - 0 7 2 . 0 5 E - 0 7 6 . 0 3 E - 0 7 8 . 5 8 E - 0 8
D a y _ r i m_ z @ 9 2 . 2 0 E - 0 7 9 . 7 1 E - 0 8 1 . 0 8 E - 0 7 4 . 7 9 E - 0 8 8 . 1 4 E - 0 7 1 . 0 5 E - 0 7
D a y _ r i m_ z @ 1 0 3 . 7 9 E - 0 7 1 . 4 8 E - 0 7 3 . 0 5 E - 0 7 1 . 2 0 E - 0 7 5 . 2 3 E - 0 7 9 . 1 2 E - 0 8
D a y _ r i m_ z @ 1 1 3 . 5 0 E - 0 7 1 . 4 6 E - 0 7 3 . 3 7 E - 0 7 1 . 4 0 E - 0 7 9 . 6 0 E - 0 7 1 . 1 1 E - 0 7
D a y _ r i m_ z @ 1 2 2 . 7 5 E - 0 7 8 . 5 9 E - 0 8 2 . 1 3 E - 0 7 6 . 6 7 E - 0 8 8 . 2 2 E - 0 7 9 . 8 0 E - 0 8
D a y _ r i m_ z @ 1 3 3 . 9 1 E - 0 7 1 . 6 5 E - 0 7 3 . 5 1 E - 0 7 1 . 4 7 E - 0 7 4 . 0 2 E - 0 7 4 . 9 7 E - 0 8
D a y _ r i m_ z @ 1 4 7 . 5 2 E - 0 7 3 . 9 7 E - 0 7 5 . 3 4 E - 0 7 2 . 8 3 E - 0 7 3 . 4 8 E - 0 7 6 . 7 1 E - 0 8
D a y _ r i m_ z @ 1 5 4 . 6 4 E - 0 7 2 . 6 3 E - 0 7 3 . 0 8 E - 0 7 1 . 8 4 E - 0 7 6 . 9 3 E - 0 7 1 . 0 7 E - 0 7
D a y _ r i m_ z @ 1 6 2 . 0 4 E - 0 7 1 . 8 1 E - 0 7 1 . 9 5 E - 0 7 1 . 7 1 E - 0 7 7 . 9 7 E - 0 7 1 . 3 9 E - 0 7
D a y _ r i m_ z @ 1 7 2 . 6 6 E - 0 7 1 . 0 2 E - 0 7 1 . 3 3 E - 0 7 5 . 0 8 E - 0 8 5 . 4 5 E - 0 7 6 . 9 8 E - 0 8
 
 
36 
 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively. 
 
S a m pl e 2 4 4 . 0 3 8 1 / 2 4 4 . 0 3 8 1 / U  O / U  O / 2 4 6 . 3 9 2 Z r  Z r  O 4
Th  O Th  O Z r 2  O 4 Z r 2  O 4
1  s.e . 1  s.e .
D a y _ r i m_ z @ 1 3 . 7 5 E - 0 6 4 . 8 3 E - 0 7 1 . 4 2 E + 0 1 7 . 1 6 E - 0 1 0 . 1 7 0 6 2 . 9 8 E + 0 4
D a y _ r i m_ z @ 2 3 . 9 6 E - 0 7 4 . 7 5 E - 0 8 1 . 3 2 E + 0 1 3 . 6 0 E - 0 1 0 . 1 8 4 1 . 7 9 E + 0 4
D a y _ r i m_ z @ 3 4 . 1 3 E - 0 7 6 . 8 8 E - 0 8 5 . 3 2 E + 0 0 9 . 0 9 E - 0 2 0 . 1 2 2 7 2 . 4 8 E + 0 4
D a y _ r i m_ z @ 4 2 . 1 8 E - 0 6 3 . 1 4 E - 0 7 5 . 9 5 E + 0 0 6 . 0 8 E - 0 2 0 . 1 6 1 1 . 9 5 E + 0 4
D a y _ r i m_ z @ 5 4 . 0 0 E - 0 7 6 . 0 6 E - 0 8 1 . 0 5 E + 0 1 1 . 3 3 E - 0 1 0 . 0 5 7 4 5 2 . 5 5 E + 0 4
D a y _ r i m_ z @ 6 4 . 7 1 E - 0 7 4 . 8 2 E - 0 8 8 . 9 2 E + 0 0 2 . 7 6 E - 0 1 0 . 1 2 8 4 3 . 3 7 E + 0 4
D a y _ r i m_ z @ 7 3 . 9 0 E - 0 7 5 . 6 4 E - 0 8 3 . 8 2 E + 0 0 3 . 7 8 E - 0 2 0 . 1 4 9 4 2 . 2 1 E + 0 4
D a y _ r i m_ z @ 8 3 . 6 1 E - 0 7 5 . 1 4 E - 0 8 6 . 4 6 E + 0 0 2 . 7 0 E - 0 1 0 . 1 5 1 3 2 . 7 4 E + 0 4
D a y _ r i m_ z @ 9 3 . 9 9 E - 0 7 5 . 0 4 E - 0 8 9 . 4 6 E + 0 0 2 . 1 6 E - 0 1 0 . 0 6 8 9 4 2 . 3 2 E + 0 4
D a y _ r i m_ z @ 1 0 4 . 4 7 E - 0 7 8 . 2 6 E - 0 8 7 . 8 1 E + 0 0 7 . 0 0 E - 0 2 0 . 1 0 1 5 2 . 1 0 E + 0 4
D a y _ r i m_ z @ 1 1 9 . 4 5 E - 0 7 1 . 0 9 E - 0 7 7 . 7 6 E + 0 0 3 . 5 6 E - 0 2 0 . 0 9 3 8 8 2 . 2 9 E + 0 4
D a y _ r i m_ z @ 1 2 6 . 2 5 E - 0 7 7 . 1 2 E - 0 8 1 . 4 1 E + 0 1 4 . 8 9 E - 0 1 0 . 1 7 2 5 2 . 7 0 E + 0 4
D a y _ r i m_ z @ 1 3 3 . 6 5 E - 0 7 4 . 5 2 E - 0 8 1 . 5 1 E + 0 1 4 . 0 7 E - 0 1 0 . 2 0 5 1 2 . 4 4 E + 0 4
D a y _ r i m_ z @ 1 4 2 . 5 0 E - 0 7 4 . 8 1 E - 0 8 8 . 4 8 E + 0 0 6 . 2 1 E - 0 2 0 . 1 9 3 5 2 . 0 6 E + 0 4
D a y _ r i m_ z @ 1 5 4 . 3 8 E - 0 7 6 . 7 6 E - 0 8 6 . 9 3 E + 0 0 2 . 1 7 E - 0 1 0 . 0 9 1 9 6 1 . 9 6 E + 0 4
D a y _ r i m_ z @ 1 6 7 . 5 0 E - 0 7 1 . 3 1 E - 0 7 4 . 7 1 E + 0 0 4 . 3 2 E - 0 2 0 . 0 2 8 7 4 1 . 9 1 E + 0 4
D a y _ r i m_ z @ 1 7 2 . 7 6 E - 0 7 3 . 5 4 E - 0 8 1 . 3 0 E + 0 1 1 . 0 8 E - 0 1 0 . 1 0 5 3 1 . 9 6 E + 0 4
 
 
 
37 
 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively. 
 
S a m pl e 2 4 6 . 0 2 8 0 4 2 4 4 . 0 3 8 1 2 4 8 . 3 2 5 4 . 3 U  O / U  O /
2 3 5 U  O 2 3 5 U  O
1  s.e . 
D a y _ r i m_ z @ 1 8 . 4 6 2 1 . 4 0 E + 0 0 4 . 6 7 E + 0 2 - 3 . 8 3 E + 0 2 1 . 3 6 E + 0 2 5 . 0 3 E - 0 1
D a y _ r i m_ z @ 2 4 . 1 3 3 2 . 6 4 E - 0 1 4 . 2 4 E + 0 2 - 5 . 9 1 E + 0 2 1 . 3 8 E + 0 2 1 . 0 8 E + 0 0
D a y _ r i m_ z @ 3 2 . 2 2 8 1 . 3 3 E - 0 1 5 . 3 1 E + 0 2 - 1 . 7 7 E + 0 3 1 . 3 5 E + 0 2 1 . 1 2 E + 0 0
D a y _ r i m_ z @ 4 1 . 7 9 9 3 . 8 3 E - 0 1 1 . 7 5 E + 0 2 - 1 . 3 3 E + 0 3 1 . 3 8 E + 0 2 1 . 0 6 E + 0 0
D a y _ r i m_ z @ 5 3 . 3 8 1 1 . 5 0 E - 0 1 1 . 0 7 E + 0 3 - 8 . 8 5 E + 0 2 1 . 3 8 E + 0 2 1 . 5 8 E + 0 0
D a y _ r i m_ z @ 6 4 . 1 3 8 3 . 2 9 E - 0 1 4 . 2 1 E + 0 2 - 1 . 1 7 E + 0 3 1 . 3 9 E + 0 2 8 . 6 8 E - 0 1
D a y _ r i m_ z @ 7 1 . 8 7 1 . 6 5 E - 0 1 2 . 2 2 E + 0 2 - 1 . 5 1 E + 0 3 1 . 3 8 E + 0 2 1 . 7 9 E + 0 0
D a y _ r i m_ z @ 8 3 . 0 3 3 1 . 7 1 E - 0 1 1 . 1 3 E + 0 2 - 6 . 6 5 E + 0 2 1 . 3 8 E + 0 2 7 . 8 3 E - 0 1
D a y _ r i m_ z @ 9 3 . 7 8 5 2 . 6 5 E - 0 1 9 . 5 2 E + 0 2 - 1 . 5 6 E + 0 3 1 . 1 6 E + 0 2 9 . 6 8 E - 0 1
D a y _ r i m_ z @ 1 0 2 . 4 1 8 1 . 3 3 E - 0 1 4 . 1 2 E + 0 2 - 7 . 8 0 E + 0 2 1 . 3 7 E + 0 2 1 . 1 7 E + 0 0
D a y _ r i m_ z @ 1 1 2 . 7 3 9 2 . 5 8 E - 0 1 3 . 6 7 E + 0 2 - 1 . 0 1 E + 0 3 1 . 3 3 E + 0 2 9 . 8 0 E - 0 1
D a y _ r i m_ z @ 1 2 6 . 1 5 1 4 . 6 0 E - 0 1 1 . 3 4 E + 0 2 - 1 . 2 9 E + 0 3 1 . 3 9 E + 0 2 5 . 2 8 E - 0 1
D a y _ r i m_ z @ 1 3 4 . 8 2 4 2 . 2 5 E - 0 1 7 . 8 7 E + 0 0 - 1 . 0 1 E + 0 3 1 . 3 8 E + 0 2 6 . 4 1 E - 0 1
D a y _ r i m_ z @ 1 4 2 . 8 5 6 9 . 2 7 E - 0 2 6 . 0 5 E + 0 2 - 1 . 0 3 E + 0 3 1 . 3 8 E + 0 2 1 . 0 4 E + 0 0
D a y _ r i m_ z @ 1 5 2 . 3 1 1 1 . 4 5 E - 0 1 7 . 6 2 E + 0 2 - 1 . 5 0 E + 0 3 1 . 3 6 E + 0 2 1 . 1 4 E + 0 0
D a y _ r i m_ z @ 1 6 1 . 5 6 3 1 . 1 4 E - 0 1 4 . 7 2 E + 0 2 - 3 . 1 1 E + 0 2 1 . 3 9 E + 0 2 1 . 5 6 E + 0 0
D a y _ r i m_ z @ 1 7 4 . 2 2 7 2 . 1 0 E - 0 1 1 . 0 5 E + 0 3 - 9 . 7 4 E + 0 2 1 . 3 7 E + 0 2 6 . 5 0 E - 0 1
 
 
 
38 
 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively. 
 
S a m pl e 2 5 1 . 0 3 8 8 5 / 2 5 1 . 0 3 8 8 5 / B c k gr
2 3 5 U  O 2 3 5 U  O U  O U  O Th  O Th  O
1  s.e . 1  s.e . 1  s.e . 
D a y _ r i m_ z @ 1 9 . 6 3 E - 0 1 5 . 0 0 E - 0 3 1 . 3 3 2 E - 0 6 2 . 3 3 E - 0 7 2 . 0 6 E - 0 6 3 . 5 3 E - 0 7
D a y _ r i m_ z @ 2 9 . 6 9 E - 0 1 6 . 4 0 E - 0 3 5 . 8 4 8 E - 0 7 1 . 2 6 E - 0 7 3 . 2 5 E - 0 7 6 . 9 0 E - 0 8
D a y _ r i m_ z @ 3 9 . 7 3 E - 0 1 7 . 7 5 E - 0 3 5 . 8 3 5 E - 0 7 2 . 4 9 E - 0 7 3 . 7 3 E - 0 7 1 . 5 4 E - 0 7
D a y _ r i m_ z @ 4 9 . 8 8 E - 0 1 1 . 0 2 E - 0 2 1 . 8 2 5 E - 0 6 4 . 6 3 E - 0 7 1 . 5 5 E - 0 6 3 . 9 9 E - 0 7
D a y _ r i m_ z @ 5 9 . 6 9 E - 0 1 7 . 1 8 E - 0 3 2 . 4 4 9 E - 0 7 6 . 1 1 E - 0 8 2 . 7 6 E - 0 7 6 . 9 0 E - 0 8
D a y _ r i m_ z @ 6 9 . 7 0 E - 0 1 7 . 7 6 E - 0 3 5 . 6 7 3 E - 0 7 1 . 1 2 E - 0 7 3 . 3 4 E - 0 7 6 . 6 1 E - 0 8
D a y _ r i m_ z @ 7 9 . 8 7 E - 0 1 1 . 0 7 E - 0 2 1 . 2 1 9 E - 0 6 3 . 1 4 E - 0 7 3 . 7 0 E - 0 7 9 . 4 3 E - 0 8
D a y _ r i m_ z @ 8 9 . 7 0 E - 0 1 7 . 3 1 E - 0 3 6 . 0 3 1 E - 0 7 2 . 8 1 E - 0 7 3 . 4 9 E - 0 7 1 . 5 0 E - 0 7
D a y _ r i m_ z @ 9 9 . 7 8 E - 0 1 7 . 1 4 E - 0 3 5 . 1 6 7 E - 0 7 1 . 0 1 E - 0 7 2 . 5 4 E - 0 7 4 . 9 2 E - 0 8
D a y _ r i m_ z @ 1 0 9 . 8 3 E - 0 1 8 . 3 8 E - 0 3 4 . 5 0 8 E - 0 7 1 . 2 3 E - 0 7 3 . 7 6 E - 0 7 1 . 0 3 E - 0 7
D a y _ r i m_ z @ 1 1 9 . 6 9 E - 0 1 1 . 0 7 E - 0 2 6 . 5 5 3 E - 0 7 1 . 2 9 E - 0 7 6 . 4 1 E - 0 7 1 . 2 6 E - 0 7
D a y _ r i m_ z @ 1 2 9 . 7 7 E - 0 1 5 . 4 2 E - 0 3 5 . 4 8 2 E - 0 7 9 . 2 2 E - 0 8 4 . 1 9 E - 0 7 6 . 9 0 E - 0 8
D a y _ r i m_ z @ 1 3 9 . 6 8 E - 0 1 7 . 1 9 E - 0 3 3 . 9 6 6 E - 0 7 1 . 2 2 E - 0 7 3 . 5 8 E - 0 7 1 . 0 9 E - 0 7
D a y _ r i m_ z @ 1 4 9 . 7 3 E - 0 1 8 . 1 9 E - 0 3 5 . 4 9 7 E - 0 7 2 . 8 5 E - 0 7 3 . 9 2 E - 0 7 2 . 0 3 E - 0 7
D a y _ r i m_ z @ 1 5 9 . 6 8 E - 0 1 1 . 1 1 E - 0 2 5 . 7 8 5 E - 0 7 2 . 0 1 E - 0 7 3 . 7 3 E - 0 7 1 . 3 9 E - 0 7
D a y _ r i m_ z @ 1 6 9 . 8 0 E - 0 1 1 . 2 3 E - 0 2 5 . 0 0 3 E - 0 7 1 . 6 1 E - 0 7 4 . 7 3 E - 0 7 1 . 5 2 E - 0 7
D a y _ r i m_ z @ 1 7 9 . 7 3 E - 0 1 7 . 0 8 E - 0 3 4 . 0 5 3 E - 0 7 8 . 7 3 E - 0 8 2 . 0 5 E - 0 7 4 . 3 8 E - 0 8
 
 
  
39 
 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively. 
 
( 2 4 6 . 3  o n l y )
S a m pl e 2 4 6 . 0 2 9 / 2 4 6 . 0 2 9 / U  O / U  O / 2 4 6 . 0 2 9 / 2 4 6 . 0 2 9 /
U  O U  O Th  O Th  O Th  O Th  O
1  s.e . 1  s.e . 1  s.e . 
D a y _ r i m_ z @ 1 1 . 2 7 0 E - 0 5 7 . 3 4 7 E - 0 7 1 . 5 6 2 E + 0 0 5 . 5 3 7 E - 0 3 1 . 9 7 6 E - 0 5 1 . 0 8 0 E - 0 6
D a y _ r i m_ z @ 2 1 . 0 3 4 E - 0 5 3 . 5 0 0 E - 0 7 5 . 5 2 0 E - 0 1 1 . 0 3 0 E - 0 2 5 . 6 9 0 E - 0 6 1 . 9 9 9 E - 0 7
D a y _ r i m_ z @ 3 1 . 0 1 1 E - 0 5 5 . 3 6 6 E - 0 7 6 . 5 4 5 E - 0 1 6 . 1 5 0 E - 0 3 6 . 6 2 9 E - 0 6 3 . 4 3 1 E - 0 7
D a y _ r i m_ z @ 4 1 . 1 0 8 E - 0 5 7 . 9 5 8 E - 0 7 8 . 4 5 2 E - 0 1 5 . 4 7 2 E - 0 3 9 . 3 2 4 E - 0 6 6 . 7 3 5 E - 0 7
D a y _ r i m_ z @ 5 7 . 8 4 5 E - 0 6 2 . 6 3 6 E - 0 7 1 . 1 0 9 E + 0 0 1 . 8 6 0 E - 0 2 8 . 6 9 1 E - 0 6 2 . 9 2 6 E - 0 7
D a y _ r i m_ z @ 6 1 . 0 0 0 E - 0 5 3 . 2 7 8 E - 0 7 5 . 9 1 6 E - 0 1 2 . 3 8 4 E - 0 3 5 . 9 1 9 E - 0 6 1 . 9 3 9 E - 0 7
D a y _ r i m_ z @ 7 1 . 3 2 1 E - 0 5 8 . 7 1 9 E - 0 7 3 . 0 7 6 E - 0 1 4 . 3 0 2 E - 0 3 4 . 1 0 2 E - 0 6 2 . 9 2 6 E - 0 7
D a y _ r i m_ z @ 8 9 . 8 0 7 E - 0 6 5 . 2 2 7 E - 0 7 6 . 2 2 5 E - 0 1 1 . 9 2 5 E - 0 2 6 . 1 1 6 E - 0 6 3 . 2 3 4 E - 0 7
D a y _ r i m_ z @ 9 1 . 1 3 8 E - 0 5 3 . 6 3 2 E - 0 7 4 . 9 4 1 E - 0 1 3 . 0 6 3 E - 0 3 5 . 6 1 2 E - 0 6 1 . 7 9 1 E - 0 7
D a y _ r i m_ z @ 1 0 8 . 8 6 2 E - 0 6 3 . 7 9 1 E - 0 7 8 . 3 2 6 E - 0 1 1 . 3 5 1 E - 0 2 7 . 4 0 6 E - 0 6 3 . 4 9 3 E - 0 7
D a y _ r i m_ z @ 1 1 9 . 8 3 0 E - 0 6 3 . 8 9 5 E - 0 7 9 . 7 6 1 E - 0 1 9 . 0 8 3 E - 0 3 9 . 6 1 1 E - 0 6 3 . 7 9 7 E - 0 7
D a y _ r i m_ z @ 1 2 9 . 8 8 6 E - 0 6 2 . 7 5 2 E - 0 7 7 . 6 8 9 E - 0 1 3 . 3 5 6 E - 0 3 7 . 5 9 2 E - 0 6 2 . 0 1 8 E - 0 7
D a y _ r i m_ z @ 1 3 8 . 2 3 0 E - 0 6 2 . 9 6 2 E - 0 7 9 . 1 2 2 E - 0 1 6 . 7 8 3 E - 0 3 7 . 4 9 0 E - 0 6 2 . 5 6 1 E - 0 7
D a y _ r i m_ z @ 1 4 9 . 8 4 8 E - 0 6 5 . 4 1 6 E - 0 7 7 . 2 1 3 E - 0 1 3 . 7 4 5 E - 0 3 7 . 1 1 1 E - 0 6 3 . 8 8 0 E - 0 7
D a y _ r i m_ z @ 1 5 1 . 0 3 0 E - 0 5 5 . 2 1 1 E - 0 7 6 . 3 0 4 E - 0 1 1 . 1 7 3 E - 0 2 6 . 4 7 6 E - 0 6 3 . 5 6 0 E - 0 7
D a y _ r i m_ z @ 1 6 1 . 0 8 7 E - 0 5 5 . 5 0 2 E - 0 7 9 . 3 6 6 E - 0 1 7 . 1 2 3 E - 0 3 1 . 0 1 5 E - 0 5 5 . 1 5 3 E - 0 7
D a y _ r i m_ z @ 1 7 1 . 0 5 5 E - 0 5 3 . 5 0 7 E - 0 7 5 . 0 3 4 E - 0 1 3 . 4 1 4 E - 0 3 5 . 3 1 5 E - 0 6 1 . 8 0 1 E - 0 7
 
 
40 
 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively. 
 
S a m pl e 2 4 6 . 0 2 9 / 2 4 6 . 0 2 9 / U  O / U  O / 2 4 6 . 0 2 9 / 2 4 6 . 0 2 9 /
U  O U  O Th  O Th  O Th  O Th  O
1  s.e . 1  s.e . 1  s.e . 
D a y _ r i m_ z @ 1 1 . 1 6 1 E - 0 5 7 . 6 6 7 E - 0 7 1 . 5 6 2 E + 0 0 5 . 5 3 7 E - 0 3 1 . 8 0 7 E - 0 5 1 . 1 2 9 E - 0 6
D a y _ r i m_ z @ 2 1 . 0 2 2 E - 0 5 3 . 3 6 4 E - 0 7 5 . 5 2 0 E - 0 1 1 . 0 3 0 E - 0 2 5 . 6 2 0 E - 0 6 1 . 9 3 5 E - 0 7
D a y _ r i m_ z @ 3 1 . 0 0 6 E - 0 5 4 . 8 7 3 E - 0 7 6 . 5 4 5 E - 0 1 6 . 1 5 0 E - 0 3 6 . 5 8 9 E - 0 6 3 . 1 4 2 E - 0 7
D a y _ r i m_ z @ 4 1 . 0 3 2 E - 0 5 7 . 4 7 6 E - 0 7 8 . 4 5 2 E - 0 1 5 . 4 7 2 E - 0 3 8 . 6 9 2 E - 0 6 6 . 2 6 8 E - 0 7
D a y _ r i m_ z @ 5 7 . 7 3 4 E - 0 6 2 . 6 2 0 E - 0 7 1 . 1 0 9 E + 0 0 1 . 8 6 0 E - 0 2 8 . 5 6 6 E - 0 6 2 . 9 0 7 E - 0 7
D a y _ r i m_ z @ 6 9 . 7 7 3 E - 0 6 3 . 1 8 8 E - 0 7 5 . 9 1 6 E - 0 1 2 . 3 8 4 E - 0 3 5 . 7 8 2 E - 0 6 1 . 8 8 5 E - 0 7
D a y _ r i m_ z @ 7 1 . 3 1 6 E - 0 5 8 . 3 3 8 E - 0 7 3 . 0 7 6 E - 0 1 4 . 3 0 2 E - 0 3 4 . 0 8 2 E - 0 6 2 . 8 2 6 E - 0 7
D a y _ r i m_ z @ 8 9 . 8 0 7 E - 0 6 4 . 4 9 3 E - 0 7 6 . 2 2 5 E - 0 1 1 . 9 2 5 E - 0 2 6 . 1 0 4 E - 0 6 2 . 9 1 2 E - 0 7
D a y _ r i m_ z @ 9 1 . 1 0 8 E - 0 5 3 . 6 4 2 E - 0 7 4 . 9 4 1 E - 0 1 3 . 0 6 3 E - 0 3 5 . 4 6 6 E - 0 6 1 . 7 9 5 E - 0 7
D a y _ r i m_ z @ 1 0 8 . 7 9 0 E - 0 6 3 . 7 0 0 E - 0 7 8 . 3 2 6 E - 0 1 1 . 3 5 1 E - 0 2 7 . 3 3 5 E - 0 6 3 . 4 3 8 E - 0 7
D a y _ r i m_ z @ 1 1 9 . 5 2 5 E - 0 6 3 . 8 3 8 E - 0 7 9 . 7 6 1 E - 0 1 9 . 0 8 3 E - 0 3 9 . 3 0 7 E - 0 6 3 . 7 4 7 E - 0 7
D a y _ r i m_ z @ 1 2 9 . 6 1 2 E - 0 6 2 . 7 7 2 E - 0 7 7 . 6 8 9 E - 0 1 3 . 3 5 6 E - 0 3 7 . 3 8 6 E - 0 6 2 . 0 2 6 E - 0 7
D a y _ r i m_ z @ 1 3 8 . 2 2 4 E - 0 6 2 . 7 4 6 E - 0 7 9 . 1 2 2 E - 0 1 6 . 7 8 3 E - 0 3 7 . 4 8 3 E - 0 6 2 . 3 6 2 E - 0 7
D a y _ r i m_ z @ 1 4 1 . 0 0 5 E - 0 5 4 . 6 5 5 E - 0 7 7 . 2 1 3 E - 0 1 3 . 7 4 5 E - 0 3 7 . 2 5 3 E - 0 6 3 . 3 4 2 E - 0 7
D a y _ r i m_ z @ 1 5 1 . 0 1 8 E - 0 5 4 . 9 2 5 E - 0 7 6 . 3 0 4 E - 0 1 1 . 1 7 3 E - 0 2 6 . 4 1 1 E - 0 6 3 . 3 4 8 E - 0 7
D a y _ r i m_ z @ 1 6 1 . 0 5 7 E - 0 5 5 . 4 4 2 E - 0 7 9 . 3 6 6 E - 0 1 7 . 1 2 3 E - 0 3 9 . 8 7 7 E - 0 6 5 . 0 9 4 E - 0 7
D a y _ r i m_ z @ 1 7 1 . 0 4 1 E - 0 5 3 . 4 6 8 E - 0 7 5 . 0 3 4 E - 0 1 3 . 4 1 4 E - 0 3 5 . 2 4 3 E - 0 6 1 . 7 8 3 E - 0 7
( a v e r a g e  2 4 6 . 3  +  2 4 4 . 0 3 8 )
 
 
41 
 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively. 
 
S a m pl e 2 4 6 . 0 2 9 / 2 4 6 . 0 2 9 / U  O / U  O / 2 4 6 . 0 2 9 / 2 4 6 . 0 2 9 /
U  O U  O Th  O Th  O Th  O Th  O
1  s.e . 1  s.e . 1  s.e . 
D a y _ r i m_ z @ 1 1 . 1 6 6 E - 0 5 7 . 7 0 4 E - 0 7 1 . 5 6 2 E + 0 0 5 . 5 3 7 E - 0 3 1 . 8 1 5 E - 0 5 1 . 1 3 5 E - 0 6
D a y _ r i m_ z @ 2 1 . 0 2 6 E - 0 5 3 . 3 8 0 E - 0 7 5 . 5 2 0 E - 0 1 1 . 0 3 0 E - 0 2 5 . 6 4 7 E - 0 6 1 . 9 4 4 E - 0 7
D a y _ r i m_ z @ 3 1 . 0 1 0 E - 0 5 4 . 8 9 6 E - 0 7 6 . 5 4 5 E - 0 1 6 . 1 5 0 E - 0 3 6 . 6 2 0 E - 0 6 3 . 1 5 7 E - 0 7
D a y _ r i m_ z @ 4 1 . 0 3 6 E - 0 5 7 . 5 1 2 E - 0 7 8 . 4 5 2 E - 0 1 5 . 4 7 2 E - 0 3 8 . 7 3 3 E - 0 6 6 . 2 9 8 E - 0 7
D a y _ r i m_ z @ 5 7 . 7 7 1 E - 0 6 2 . 6 3 3 E - 0 7 1 . 1 0 9 E + 0 0 1 . 8 6 0 E - 0 2 8 . 6 0 7 E - 0 6 2 . 9 2 1 E - 0 7
D a y _ r i m_ z @ 6 9 . 8 1 9 E - 0 6 3 . 2 0 4 E - 0 7 5 . 9 1 6 E - 0 1 2 . 3 8 4 E - 0 3 5 . 8 0 9 E - 0 6 1 . 8 9 4 E - 0 7
D a y _ r i m_ z @ 7 1 . 3 2 2 E - 0 5 8 . 3 7 8 E - 0 7 3 . 0 7 6 E - 0 1 4 . 3 0 2 E - 0 3 4 . 1 0 2 E - 0 6 2 . 8 4 0 E - 0 7
D a y _ r i m_ z @ 8 9 . 8 5 4 E - 0 6 4 . 5 1 4 E - 0 7 6 . 2 2 5 E - 0 1 1 . 9 2 5 E - 0 2 6 . 1 3 3 E - 0 6 2 . 9 2 6 E - 0 7
D a y _ r i m_ z @ 9 1 . 1 1 4 E - 0 5 3 . 6 6 0 E - 0 7 4 . 9 4 1 E - 0 1 3 . 0 6 3 E - 0 3 5 . 4 9 2 E - 0 6 1 . 8 0 3 E - 0 7
D a y _ r i m_ z @ 1 0 8 . 8 3 2 E - 0 6 3 . 7 1 8 E - 0 7 8 . 3 2 6 E - 0 1 1 . 3 5 1 E - 0 2 7 . 3 7 0 E - 0 6 3 . 4 5 5 E - 0 7
D a y _ r i m_ z @ 1 1 9 . 5 7 0 E - 0 6 3 . 8 5 6 E - 0 7 9 . 7 6 1 E - 0 1 9 . 0 8 3 E - 0 3 9 . 3 5 2 E - 0 6 3 . 7 6 4 E - 0 7
D a y _ r i m_ z @ 1 2 9 . 6 5 8 E - 0 6 2 . 7 8 5 E - 0 7 7 . 6 8 9 E - 0 1 3 . 3 5 6 E - 0 3 7 . 4 2 1 E - 0 6 2 . 0 3 6 E - 0 7
D a y _ r i m_ z @ 1 3 8 . 2 6 4 E - 0 6 2 . 7 5 9 E - 0 7 9 . 1 2 2 E - 0 1 6 . 7 8 3 E - 0 3 7 . 5 1 9 E - 0 6 2 . 3 7 3 E - 0 7
D a y _ r i m_ z @ 1 4 1 . 0 1 0 E - 0 5 4 . 6 7 7 E - 0 7 7 . 2 1 3 E - 0 1 3 . 7 4 5 E - 0 3 7 . 2 8 8 E - 0 6 3 . 3 5 8 E - 0 7
D a y _ r i m_ z @ 1 5 1 . 0 2 3 E - 0 5 4 . 9 4 8 E - 0 7 6 . 3 0 4 E - 0 1 1 . 1 7 3 E - 0 2 6 . 4 4 1 E - 0 6 3 . 3 6 4 E - 0 7
D a y _ r i m_ z @ 1 6 1 . 0 6 2 E - 0 5 5 . 4 6 7 E - 0 7 9 . 3 6 6 E - 0 1 7 . 1 2 3 E - 0 3 9 . 9 2 4 E - 0 6 5 . 1 1 8 E - 0 7
D a y _ r i m_ z @ 1 7 1 . 0 4 6 E - 0 5 3 . 4 8 4 E - 0 7 5 . 0 3 4 E - 0 1 3 . 4 1 4 E - 0 3 5 . 2 6 8 E - 0 6 1 . 7 9 1 E - 0 7
g a i n  c o r r e c te d  ( a v e r a g e  g a i n  1 . 0 0 5 E + 0 0 )
 
  
42 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively. 
 
S a m pl e 2 4 6 . 0 2 8 0 4 / 2 4 6 . 0 2 8 0 4 / U  O / U  O / 2 4 6 . 0 2 8 0 4 / 2 4 6 . 0 2 8 0 4 /
U  O U  O Th  O Th  O Th  O Th  O
1  s.e . 1  s.e . 1  s.e .
D a y _ i n t_ z @ 1 8 . 8 5 E - 0 6 1 . 5 1 E - 0 7 1 . 4 6 E + 0 0 1 . 1 5 E - 0 2 1 . 2 9 E - 0 5 2 . 4 4 E - 0 7
D a y _ i n t_ z @ 2 1 . 0 2 E - 0 5 3 . 6 5 E - 0 7 6 . 5 7 E - 0 1 1 . 1 8 E - 0 2 6 . 6 9 E - 0 6 2 . 4 0 E - 0 7
D a y _ i n t_ z @ 3 8 . 8 2 E - 0 6 3 . 8 2 E - 0 7 5 . 9 7 E - 0 1 6 . 1 1 E - 0 3 5 . 2 7 E - 0 6 2 . 2 9 E - 0 7
D a y _ i n t_ z @ 4 1 . 0 7 E - 0 5 4 . 2 1 E - 0 7 5 . 5 1 E - 0 1 6 . 9 5 E - 0 3 5 . 9 1 E - 0 6 2 . 3 2 E - 0 7
D a y _ i n t_ z @ 5 1 . 0 1 E - 0 5 4 . 4 6 E - 0 7 5 . 4 0 E - 0 1 1 . 9 1 E - 0 2 5 . 3 9 E - 0 6 2 . 3 7 E - 0 7
D a y _ i n t_ z @ 6 1 . 1 0 E - 0 5 3 . 4 0 E - 0 7 4 . 9 0 E - 0 1 4 . 0 3 E - 0 3 5 . 4 0 E - 0 6 1 . 6 7 E - 0 7
D a y _ i n t_ z @ 7 1 . 2 9 E - 0 5 5 . 5 2 E - 0 7 2 . 7 0 E - 0 1 2 . 4 4 E - 0 3 3 . 4 6 E - 0 6 1 . 4 9 E - 0 7
D a y _ i n t_ z @ 8 1 . 1 5 E - 0 5 4 . 9 0 E - 0 7 3 . 5 6 E - 0 1 2 . 8 7 E - 0 3 4 . 0 7 E - 0 6 1 . 7 4 E - 0 7
D a y _ i n t_ z @ 9 1 . 3 4 E - 0 5 3 . 8 6 E - 0 7 3 . 2 2 E - 0 1 2 . 5 8 E - 0 3 4 . 3 0 E - 0 6 1 . 2 0 E - 0 7
D a y _ i n t_ z @ 1 0 1 . 0 6 E - 0 5 3 . 8 3 E - 0 7 5 . 9 6 E - 0 1 8 . 1 9 E - 0 3 6 . 3 6 E - 0 6 2 . 7 5 E - 0 7
D a y _ i n t_ z @ 1 1 9 . 4 7 E - 0 6 2 . 6 7 E - 0 7 6 . 1 3 E - 0 1 6 . 4 1 E - 0 3 5 . 8 0 E - 0 6 1 . 6 4 E - 0 7
D a y _ i n t_ z @ 1 2 9 . 5 2 E - 0 6 1 . 9 5 E - 0 7 7 . 1 5 E - 0 1 1 . 7 3 E - 0 3 6 . 8 0 E - 0 6 1 . 3 9 E - 0 7
D a y _ i n t_ z @ 1 3 9 . 3 9 E - 0 6 3 . 2 1 E - 0 7 6 . 6 5 E - 0 1 8 . 8 5 E - 0 3 6 . 2 3 E - 0 6 2 . 1 3 E - 0 7
D a y _ i n t_ z @ 1 4 1 . 1 3 E - 0 5 1 . 4 0 E - 0 6 6 . 4 2 E - 0 1 5 . 4 0 E - 0 3 7 . 2 7 E - 0 6 9 . 3 4 E - 0 7
D a y _ i n t_ z @ 1 5 1 . 0 2 E - 0 5 3 . 9 0 E - 0 7 5 . 8 3 E - 0 1 4 . 5 9 E - 0 3 5 . 9 6 E - 0 6 2 . 2 8 E - 0 7
D a y _ i n t_ z @ 1 6 1 . 4 0 E - 0 5 5 . 8 8 E - 0 7 1 . 5 0 E + 0 0 2 . 3 3 E - 0 2 2 . 0 9 E - 0 5 9 . 0 9 E - 0 7
D a y _ i n t_ z @ 1 7 1 . 0 2 E - 0 5 3 . 3 2 E - 0 7 5 . 2 7 E - 0 1 6 . 0 4 E - 0 3 5 . 3 8 E - 0 6 1 . 7 5 E - 0 7
D a y _ i n t_ z @ 1 8 8 . 0 5 E - 0 6 4 . 6 1 E - 0 7 1 . 4 9 E + 0 0 1 . 5 9 E - 0 2 1 . 1 9 E - 0 5 6 . 8 3 E - 0 7
D a y _ i n t_ z @ 1 9 1 . 1 1 E - 0 5 3 . 8 0 E - 0 7 4 . 6 3 E - 0 1 1 . 7 0 E - 0 3 5 . 1 5 E - 0 6 1 . 7 6 E - 0 7
D a y _ i n t_ z @ 2 1 9 . 2 6 E - 0 6 2 . 1 2 E - 0 7 6 . 3 3 E - 0 1 2 . 6 6 E - 0 3 5 . 8 6 E - 0 6 1 . 3 4 E - 0 7
D a y _ i n t_ z @ 2 2 1 . 0 3 E - 0 5 3 . 0 2 E - 0 7 5 . 6 3 E - 0 1 9 . 4 4 E - 0 3 5 . 8 3 E - 0 6 2 . 1 3 E - 0 7
D a y _ i n t_ z @ 2 3 1 . 0 3 E - 0 5 3 . 5 2 E - 0 7 4 . 5 9 E - 0 1 1 . 7 3 E - 0 3 4 . 7 3 E - 0 6 1 . 6 2 E - 0 7
 
43 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively. 
  
S a m pl e 2 4 6 . 3 / 2 4 6 . 3 / 2 4 6 . 3 / 2 4 6 . 3 / 2 4 4 . 0 3 8 1 / 2 4 4 . 0 3 8 1 /
U  O U  O Th  O Th  O U  O U  O
1  s.e . 1  s.e . 1  s.e .
D a y _ i n t_ z @ 1 2 . 3 5 E - 0 8 1 . 5 8 E - 0 8 3 . 3 7 E - 0 8 2 . 2 6 E - 0 8 1 . 3 1 E - 0 7 1 . 9 1 E - 0 8
D a y _ i n t_ z @ 2 7 . 5 0 E - 0 8 6 . 8 2 E - 0 8 4 . 6 7 E - 0 8 4 . 2 1 E - 0 8 4 . 2 7 E - 0 7 7 . 5 3 E - 0 8
D a y _ i n t_ z @ 3 1 . 0 9 E - 0 7 8 . 3 7 E - 0 8 6 . 8 2 E - 0 8 5 . 2 1 E - 0 8 7 . 9 5 E - 0 7 1 . 1 5 E - 0 7
D a y _ i n t_ z @ 4 3 . 4 1 E - 0 7 1 . 9 6 E - 0 7 1 . 9 0 E - 0 7 1 . 1 3 E - 0 7 5 . 4 2 E - 0 7 9 . 4 7 E - 0 8
D a y _ i n t_ z @ 5 2 . 5 9 E - 0 7 1 . 4 7 E - 0 7 1 . 4 3 E - 0 7 8 . 2 8 E - 0 8 9 . 9 3 E - 0 7 1 . 5 8 E - 0 7
D a y _ i n t_ z @ 6 2 . 4 4 E - 0 7 1 . 0 8 E - 0 7 1 . 2 0 E - 0 7 5 . 3 8 E - 0 8 3 . 1 8 E - 0 7 5 . 8 2 E - 0 8
D a y _ i n t_ z @ 7 7 . 2 2 E - 0 7 2 . 7 6 E - 0 7 1 . 9 3 E - 0 7 7 . 4 2 E - 0 8 1 . 0 2 E - 0 6 1 . 5 6 E - 0 7
D a y _ i n t_ z @ 8 2 . 5 8 E - 0 7 1 . 3 6 E - 0 7 9 . 2 8 E - 0 8 4 . 8 7 E - 0 8 8 . 2 9 E - 0 7 1 . 3 9 E - 0 7
D a y _ i n t_ z @ 9 4 . 2 9 E - 0 7 1 . 7 6 E - 0 7 1 . 3 8 E - 0 7 5 . 7 9 E - 0 8 8 . 7 5 E - 0 7 9 . 3 4 E - 0 8
D a y _ i n t_ z @ 1 0 3 . 9 9 E - 0 7 1 . 9 3 E - 0 7 2 . 3 6 E - 0 7 1 . 1 7 E - 0 7 5 . 3 4 E - 0 7 7 . 7 0 E - 0 8
D a y _ i n t_ z @ 1 1 3 . 5 5 E - 0 7 1 . 0 4 E - 0 7 2 . 1 5 E - 0 7 6 . 3 0 E - 0 8 3 . 4 8 E - 0 7 5 . 1 8 E - 0 8
D a y _ i n t_ z @ 1 2 1 . 0 6 E - 0 7 4 . 4 4 E - 0 8 7 . 5 7 E - 0 8 3 . 1 7 E - 0 8 2 . 4 7 E - 0 7 3 . 1 4 E - 0 8
D a y _ i n t_ z @ 1 3 3 . 1 2 E - 0 7 1 . 1 2 E - 0 7 2 . 1 3 E - 0 7 7 . 7 2 E - 0 8 5 . 1 1 E - 0 7 7 . 3 9 E - 0 8
D a y _ i n t_ z @ 1 4 1 . 9 6 E - 0 7 1 . 1 4 E - 0 7 1 . 2 4 E - 0 7 7 . 2 5 E - 0 8 4 . 4 1 E - 0 7 7 . 0 5 E - 0 8
D a y _ i n t_ z @ 1 5 5 . 6 2 E - 0 7 1 . 8 2 E - 0 7 3 . 2 2 E - 0 7 1 . 0 4 E - 0 7 4 . 6 0 E - 0 7 8 . 3 1 E - 0 8
D a y _ i n t_ z @ 1 6 2 . 4 4 E - 0 7 1 . 6 3 E - 0 7 3 . 7 1 E - 0 7 2 . 4 7 E - 0 7 8 . 1 8 E - 0 7 1 . 4 3 E - 0 7
D a y _ i n t_ z @ 1 7 2 . 5 7 E - 0 7 1 . 1 5 E - 0 7 1 . 3 2 E - 0 7 5 . 8 5 E - 0 8 4 . 6 2 E - 0 7 7 . 1 3 E - 0 8
D a y _ i n t_ z @ 1 8 6 . 5 2 E - 0 7 2 . 8 9 E - 0 7 1 . 0 1 E - 0 6 4 . 4 6 E - 0 7 7 . 0 6 E - 0 7 1 . 3 6 E - 0 7
D a y _ i n t_ z @ 1 9 3 . 4 3 E - 0 7 1 . 2 3 E - 0 7 1 . 5 8 E - 0 7 5 . 6 5 E - 0 8 4 . 5 7 E - 0 7 7 . 7 2 E - 0 8
D a y _ i n t_ z @ 2 1 1 . 2 6 E - 0 7 5 . 5 8 E - 0 8 7 . 9 0 E - 0 8 3 . 4 7 E - 0 8 3 . 2 2 E - 0 7 3 . 9 5 E - 0 8
D a y _ i n t_ z @ 2 2 5 . 8 8 E - 0 8 4 . 9 0 E - 0 8 3 . 3 4 E - 0 8 2 . 8 3 E - 0 8 9 . 8 4 E - 0 7 9 . 3 4 E - 0 8
D a y _ i n t_ z @ 2 3 4 . 3 6 E - 0 7 1 . 6 9 E - 0 7 1 . 9 9 E - 0 7 7 . 7 4 E - 0 8 2 . 0 7 E - 0 6 1 . 5 8 E - 0 7
 
44 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively.  
 
S a m pl e 2 4 4 . 0 3 8 1 / 2 4 4 . 0 3 8 1 / U  O / U  O / 2 4 6 . 3 9 2 Z r  Z r  O 4
Th  O Th  O Z r 2  O 4 Z r 2  O 4
1  s.e . 1  s.e .
D a y _ i n t_ z @ 1 1 . 9 0 E - 0 7 2 . 7 2 E - 0 8 3 . 7 9 E + 0 1 1 . 3 2 E + 0 0 0 . 0 3 4 4 5 2 . 3 4 E + 0 4
D a y _ i n t_ z @ 2 2 . 8 6 E - 0 7 5 . 0 4 E - 0 8 7 . 5 9 E + 0 0 1 . 5 5 E - 0 1 0 . 0 2 1 0 7 2 . 2 2 E + 0 4
D a y _ i n t_ z @ 3 4 . 7 7 E - 0 7 6 . 8 9 E - 0 8 5 . 6 6 E + 0 0 3 . 8 6 E - 0 2 0 . 0 2 2 9 8 2 . 4 0 E + 0 4
D a y _ i n t_ z @ 4 2 . 9 6 E - 0 7 5 . 1 8 E - 0 8 6 . 1 7 E + 0 0 2 . 0 0 E - 0 1 0 . 0 6 8 9 5 2 . 1 3 E + 0 4
D a y _ i n t_ z @ 5 4 . 9 4 E - 0 7 7 . 0 7 E - 0 8 5 . 2 8 E + 0 0 9 . 7 3 E - 0 2 0 . 0 4 5 9 7 2 . 1 2 E + 0 4
D a y _ i n t_ z @ 6 1 . 5 7 E - 0 7 2 . 8 7 E - 0 8 9 . 7 6 E + 0 0 3 . 6 6 E - 0 1 0 . 0 7 0 8 8 2 . 1 3 E + 0 4
D a y _ i n t_ z @ 7 2 . 7 9 E - 0 7 4 . 2 7 E - 0 8 5 . 0 7 E + 0 0 8 . 9 6 E - 0 2 0 . 1 0 3 4 1 . 7 9 E + 0 4
D a y _ i n t_ z @ 8 2 . 9 8 E - 0 7 5 . 1 2 E - 0 8 5 . 6 9 E + 0 0 6 . 4 2 E - 0 2 0 . 0 4 5 9 8 1 . 9 8 E + 0 4
D a y _ i n t_ z @ 9 2 . 8 3 E - 0 7 3 . 0 2 E - 0 8 1 . 1 0 E + 0 1 2 . 3 6 E - 0 1 0 . 1 4 9 4 1 . 8 9 E + 0 4
D a y _ i n t_ z @ 1 0 3 . 2 0 E - 0 7 4 . 6 2 E - 0 8 7 . 1 5 E + 0 0 4 . 1 6 E - 0 1 0 . 1 3 4 2 . 6 6 E + 0 4
D a y _ i n t_ z @ 1 1 2 . 1 3 E - 0 7 3 . 1 8 E - 0 8 1 . 0 8 E + 0 1 1 . 8 8 E - 0 1 0 . 1 6 0 9 2 . 7 5 E + 0 4
D a y _ i n t_ z @ 1 2 1 . 7 7 E - 0 7 2 . 2 5 E - 0 8 1 . 9 7 E + 0 1 7 . 0 8 E - 0 2 0 . 0 9 1 9 3 2 . 8 7 E + 0 4
D a y _ i n t_ z @ 1 3 3 . 3 3 E - 0 7 4 . 8 1 E - 0 8 7 . 2 9 E + 0 0 2 . 9 6 E - 0 1 0 . 0 9 1 9 6 2 . 6 6 E + 0 4
D a y _ i n t_ z @ 1 4 2 . 8 0 E - 0 7 4 . 4 9 E - 0 8 7 . 1 1 E + 0 0 4 . 8 1 E - 0 2 0 . 0 5 7 5 5 2 . 7 6 E + 0 4
D a y _ i n t_ z @ 1 5 2 . 6 7 E - 0 7 4 . 8 3 E - 0 8 5 . 6 6 E + 0 0 1 . 1 2 E - 0 1 0 . 1 2 8 4 2 . 6 6 E + 0 4
D a y _ i n t_ z @ 1 6 1 . 2 1 E - 0 6 2 . 1 2 E - 0 7 3 . 3 1 E + 0 0 2 . 6 2 E - 0 2 0 . 0 3 4 5 2 2 . 6 9 E + 0 4
D a y _ i n t_ z @ 1 7 2 . 4 4 E - 0 7 3 . 7 7 E - 0 8 7 . 3 1 E + 0 0 1 . 4 1 E - 0 1 0 . 0 8 0 4 9 2 . 8 1 E + 0 4
D a y _ i n t_ z @ 1 8 1 . 0 6 E - 0 6 2 . 0 4 E - 0 7 3 . 8 1 E + 0 0 3 . 6 5 E - 0 2 0 . 0 9 0 0 2 2 . 3 5 E + 0 4
D a y _ i n t_ z @ 1 9 2 . 1 1 E - 0 7 3 . 5 6 E - 0 8 7 . 2 7 E + 0 0 3 . 5 5 E - 0 2 0 . 0 9 2 . 4 6 E + 0 4
D a y _ i n t_ z @ 2 1 2 . 0 3 E - 0 7 2 . 4 9 E - 0 8 1 . 7 7 E + 0 1 3 . 1 1 E - 0 1 0 . 0 8 8 1 4 2 . 0 5 E + 0 4
D a y _ i n t_ z @ 2 2 5 . 4 6 E - 0 7 5 . 1 2 E - 0 8 1 . 0 0 E + 0 1 2 . 4 9 E - 0 1 0 . 0 2 2 9 9 2 . 8 4 E + 0 4
D a y _ i n t_ z @ 2 3 9 . 5 0 E - 0 7 7 . 2 5 E - 0 8 5 . 8 1 E + 0 0 9 . 5 3 E - 0 2 0 . 1 2 4 5 3 . 9 0 E + 0 4
 
45 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively. 
 
S a m pl e 2 4 6 . 0 2 8 0 4 2 4 4 . 0 3 8 1 2 4 8 . 3 2 5 4 . 3 U  O / U  O /
2 3 5 U  O 2 3 5 U  O
1  s.e .
D a y _ i n t_ z @ 1 1 1 . 8 4 1 . 8 0 E - 0 1 7 . 9 8 E + 0 2 - 1 . 2 6 E + 0 3 1 . 3 7 E + 0 2 4 . 5 2 E - 0 1
D a y _ i n t_ z @ 2 2 . 6 9 1 1 . 1 1 E - 0 1 3 . 1 1 E + 0 2 - 1 . 9 0 E + 0 3 1 . 3 9 E + 0 2 1 . 0 1 E + 0 0
D a y _ i n t_ z @ 3 1 . 8 3 7 1 . 6 5 E - 0 1 3 . 2 7 E + 0 2 - 1 . 5 7 E + 0 3 1 . 3 9 E + 0 2 1 . 1 7 E + 0 0
D a y _ i n t_ z @ 4 2 . 2 4 4 1 . 1 3 E - 0 1 3 . 7 6 E + 0 2 - 1 . 4 2 E + 0 3 1 . 3 7 E + 0 2 9 . 0 9 E - 0 1
D a y _ i n t_ z @ 5 1 . 7 8 1 . 6 9 E - 0 1 - 2 . 1 2 E + 0 1 - 1 . 2 7 E + 0 3 1 . 3 8 E + 0 2 1 . 4 5 E + 0 0
D a y _ i n t_ z @ 6 3 . 6 1 9 1 . 0 3 E - 0 1 4 . 3 5 E + 0 2 - 6 . 0 5 E + 0 2 1 . 3 1 E + 0 2 8 . 2 2 E - 0 1
D a y _ i n t_ z @ 7 1 . 8 6 7 1 . 4 7 E - 0 1 - 2 . 6 1 E + 0 2 - 1 . 7 5 E + 0 3 1 . 4 1 E + 0 2 1 . 5 2 E + 0 0
D a y _ i n t_ z @ 8 1 . 8 8 2 1 . 3 6 E - 0 1 - 4 . 9 8 E + 0 2 - 1 . 4 0 E + 0 3 1 . 3 5 E + 0 2 1 . 2 9 E + 0 0
D a y _ i n t_ z @ 9 4 . 6 5 6 3 . 0 2 E - 0 1 4 . 8 4 E + 0 2 - 1 . 1 4 E + 0 3 7 . 6 7 E + 0 1 8 . 4 1 E - 0 1
D a y _ i n t_ z @ 1 0 3 . 3 8 6 1 . 6 6 E - 0 1 3 . 1 8 E + 0 2 - 1 . 4 4 E + 0 3 1 . 3 0 E + 0 2 1 . 4 1 E + 0 0
D a y _ i n t_ z @ 1 1 4 . 3 2 3 1 . 5 6 E - 0 1 3 . 4 4 E + 0 2 - 2 . 2 3 E + 0 3 1 . 3 8 E + 0 2 6 . 8 6 E - 0 1
D a y _ i n t_ z @ 1 2 8 . 2 1 4 2 . 1 3 E - 0 1 - 4 . 1 6 E + 0 2 - 1 . 8 2 E + 0 3 1 . 3 8 E + 0 2 4 . 7 5 E - 0 1
D a y _ i n t_ z @ 1 3 2 . 9 4 6 1 . 6 5 E - 0 1 - 7 . 1 2 E + 0 1 - 2 . 5 9 E + 0 3 1 . 3 2 E + 0 2 9 . 6 0 E - 0 1
D a y _ i n t_ z @ 1 4 3 . 4 3 2 1 . 3 5 E - 0 1 - 3 . 3 5 E + 0 2 - 2 . 0 9 E + 0 3 1 . 3 8 E + 0 2 9 . 8 2 E - 0 1
D a y _ i n t_ z @ 1 5 2 . 3 7 7 1 . 0 6 E - 0 1 4 . 6 0 E + 0 2 - 1 . 9 9 E + 0 3 1 . 3 8 E + 0 2 1 . 0 5 E + 0 0
D a y _ i n t_ z @ 1 6 1 . 9 3 9 1 . 1 3 E - 0 1 4 . 3 4 E + 0 1 - 2 . 2 0 E + 0 3 1 . 3 7 E + 0 2 1 . 6 6 E + 0 0
D a y _ i n t_ z @ 1 7 3 . 2 8 1 1 . 4 4 E - 0 1 3 . 1 4 E + 0 2 - 3 . 0 0 E + 0 3 1 . 3 7 E + 0 2 7 . 9 6 E - 0 1
D a y _ i n t_ z @ 1 8 1 . 0 5 1 9 . 3 1 E - 0 2 7 . 1 0 E + 0 2 - 1 . 8 8 E + 0 3 1 . 4 0 E + 0 2 1 . 8 1 E + 0 0
D a y _ i n t_ z @ 1 9 2 . 9 5 6 1 . 2 1 E - 0 1 9 . 6 2 E + 0 2 - 1 . 6 5 E + 0 3 1 . 3 9 E + 0 2 9 . 4 4 E - 0 1
D a y _ i n t_ z @ 2 1 6 . 6 0 6 2 . 2 9 E - 0 1 5 . 3 6 E + 0 2 - 1 . 7 7 E + 0 3 1 . 3 9 E + 0 2 6 . 3 1 E - 0 1
D a y _ i n t_ z @ 2 2 4 . 0 2 3 3 . 9 2 E - 0 1 - 2 . 6 0 E + 0 2 - 2 . 1 9 E + 0 3 1 . 1 8 E + 0 2 1 . 3 3 E + 0 0
D a y _ i n t_ z @ 2 3 2 . 9 4 1 5 . 9 2 E - 0 1 5 . 3 4 E + 0 2 - 1 . 8 4 E + 0 3 1 . 3 9 E + 0 2 8 . 3 1 E - 0 1
 
46 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively. 
  
S a m pl e 2 5 1 . 0 3 8 8 5 / 2 5 1 . 0 3 8 8 5 / B c k gr
2 3 5 U  O 2 3 5 U  O U  O U  O Th  O Th  O
1  s.e .
D a y _ i n t_ z @ 1 9 . 7 4 E - 0 1 4 . 1 1 E - 0 3 7 . 7 3 2 E - 0 8 1 . 7 5 E - 0 8 1 . 1 2 E - 0 7 2 . 5 0 E - 0 8
D a y _ i n t_ z @ 2 9 . 8 0 E - 0 1 7 . 4 4 E - 0 3 2 . 5 1 0 E - 0 7 7 . 1 8 E - 0 8 1 . 6 6 E - 0 7 4 . 6 5 E - 0 8
D a y _ i n t_ z @ 3 9 . 6 3 E - 0 1 7 . 5 1 E - 0 3 4 . 5 1 8 E - 0 7 1 . 0 0 E - 0 7 2 . 7 2 E - 0 7 6 . 1 1 E - 0 8
D a y _ i n t_ z @ 4 9 . 8 6 E - 0 1 8 . 9 8 E - 0 3 4 . 4 1 7 E - 0 7 1 . 5 4 E - 0 7 2 . 4 3 E - 0 7 8 . 8 0 E - 0 8
D a y _ i n t_ z @ 5 9 . 8 4 E - 0 1 1 . 4 5 E - 0 2 6 . 2 6 2 E - 0 7 1 . 5 2 E - 0 7 3 . 1 9 E - 0 7 7 . 7 0 E - 0 8
D a y _ i n t_ z @ 6 9 . 8 1 E - 0 1 7 . 2 3 E - 0 3 2 . 8 0 8 E - 0 7 8 . 6 4 E - 0 8 1 . 3 9 E - 0 7 4 . 3 1 E - 0 8
D a y _ i n t_ z @ 7 9 . 9 2 E - 0 1 1 . 3 2 E - 0 2 8 . 6 9 2 E - 0 7 2 . 2 4 E - 0 7 2 . 3 6 E - 0 7 6 . 0 5 E - 0 8
D a y _ i n t_ z @ 8 9 . 6 8 E - 0 1 8 . 8 2 E - 0 3 5 . 4 3 5 E - 0 7 1 . 3 8 E - 0 7 1 . 9 5 E - 0 7 5 . 0 0 E - 0 8
D a y _ i n t_ z @ 9 9 . 7 4 E - 0 1 5 . 7 9 E - 0 3 6 . 5 2 1 E - 0 7 1 . 4 1 E - 0 7 2 . 1 0 E - 0 7 4 . 6 2 E - 0 8
D a y _ i n t_ z @ 1 0 9 . 7 6 E - 0 1 7 . 3 2 E - 0 3 4 . 6 6 6 E - 0 7 1 . 4 7 E - 0 7 2 . 7 8 E - 0 7 8 . 9 2 E - 0 8
D a y _ i n t_ z @ 1 1 9 . 7 7 E - 0 1 7 . 6 9 E - 0 3 3 . 5 1 4 E - 0 7 8 . 1 9 E - 0 8 2 . 1 4 E - 0 7 4 . 9 9 E - 0 8
D a y _ i n t_ z @ 1 2 9 . 7 4 E - 0 1 4 . 8 5 E - 0 3 1 . 7 6 4 E - 0 7 3 . 8 4 E - 0 8 1 . 2 6 E - 0 7 2 . 7 5 E - 0 8
D a y _ i n t_ z @ 1 3 9 . 6 4 E - 0 1 9 . 3 9 E - 0 3 4 . 1 1 5 E - 0 7 9 . 4 7 E - 0 8 2 . 7 3 E - 0 7 6 . 4 3 E - 0 8
D a y _ i n t_ z @ 1 4 9 . 7 4 E - 0 1 8 . 9 4 E - 0 3 3 . 1 8 5 E - 0 7 9 . 4 6 E - 0 8 2 . 0 2 E - 0 7 6 . 0 3 E - 0 8
D a y _ i n t_ z @ 1 5 9 . 7 8 E - 0 1 9 . 0 7 E - 0 3 5 . 1 0 7 E - 0 7 1 . 4 1 E - 0 7 2 . 9 5 E - 0 7 8 . 1 2 E - 0 8
D a y _ i n t_ z @ 1 6 9 . 6 4 E - 0 1 1 . 4 5 E - 0 2 5 . 3 1 0 E - 0 7 1 . 5 3 E - 0 7 7 . 9 2 E - 0 7 2 . 3 0 E - 0 7
D a y _ i n t_ z @ 1 7 9 . 7 3 E - 0 1 7 . 1 7 E - 0 3 3 . 5 9 5 E - 0 7 9 . 5 7 E - 0 8 1 . 8 8 E - 0 7 4 . 9 2 E - 0 8
D a y _ i n t_ z @ 1 8 9 . 7 7 E - 0 1 1 . 1 5 E - 0 2 6 . 7 9 0 E - 0 7 2 . 2 6 E - 0 7 1 . 0 3 E - 0 6 3 . 4 7 E - 0 7
D a y _ i n t_ z @ 1 9 9 . 7 2 E - 0 1 8 . 1 7 E - 0 3 4 . 0 0 0 E - 0 7 1 . 0 2 E - 0 7 1 . 8 4 E - 0 7 4 . 7 2 E - 0 8
D a y _ i n t_ z @ 2 1 9 . 7 3 E - 0 1 6 . 8 0 E - 0 3 2 . 2 4 0 E - 0 7 4 . 8 4 E - 0 8 1 . 4 1 E - 0 7 3 . 0 2 E - 0 8
D a y _ i n t_ z @ 2 2 9 . 7 4 E - 0 1 7 . 6 0 E - 0 3 5 . 2 1 3 E - 0 7 7 . 4 6 E - 0 8 2 . 9 0 E - 0 7 4 . 1 4 E - 0 8
D a y _ i n t_ z @ 2 3 9 . 8 7 E - 0 1 7 . 6 7 E - 0 3 1 . 2 5 1 E - 0 6 1 . 6 3 E - 0 7 5 . 7 5 E - 0 7 7 . 5 0 E - 0 8
 
47 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively. 
 
( 2 4 6 . 3  o n l y )
S a m pl e 2 4 6 . 0 2 9 / 2 4 6 . 0 2 9 / U  O / U  O / 2 4 6 . 0 2 9 / 2 4 6 . 0 2 9 /
U  O U  O Th  O Th  O Th  O Th  O
1  s.e . 1  s.e . 1  s.e .
D a y _ i n t_ z @ 1 8 . 8 2 7 E - 0 6 1 . 5 1 9 E - 0 7 1 . 4 5 9 E + 0 0 1 . 1 4 5 E - 0 2 1 . 2 9 0 E - 0 5 2 . 4 4 7 E - 0 7
D a y _ i n t_ z @ 2 1 . 0 1 4 E - 0 5 3 . 7 1 7 E - 0 7 6 . 5 7 2 E - 0 1 1 . 1 7 7 E - 0 2 6 . 6 4 6 E - 0 6 2 . 4 3 3 E - 0 7
D a y _ i n t_ z @ 3 8 . 7 1 5 E - 0 6 3 . 9 1 3 E - 0 7 5 . 9 7 2 E - 0 1 6 . 1 1 4 E - 0 3 5 . 2 0 6 E - 0 6 2 . 3 4 4 E - 0 7
D a y _ i n t_ z @ 4 1 . 0 4 0 E - 0 5 4 . 6 4 5 E - 0 7 5 . 5 0 8 E - 0 1 6 . 9 4 6 E - 0 3 5 . 7 2 3 E - 0 6 2 . 5 8 0 E - 0 7
D a y _ i n t_ z @ 5 9 . 8 8 1 E - 0 6 4 . 6 9 9 E - 0 7 5 . 4 0 0 E - 0 1 1 . 9 1 3 E - 0 2 5 . 2 4 4 E - 0 6 2 . 5 1 1 E - 0 7
D a y _ i n t_ z @ 6 1 . 0 7 8 E - 0 5 3 . 5 6 7 E - 0 7 4 . 9 0 2 E - 0 1 4 . 0 3 2 E - 0 3 5 . 2 8 2 E - 0 6 1 . 7 5 2 E - 0 7
D a y _ i n t_ z @ 7 1 . 2 1 3 E - 0 5 6 . 1 7 4 E - 0 7 2 . 6 9 5 E - 0 1 2 . 4 4 1 E - 0 3 3 . 2 6 2 E - 0 6 1 . 6 6 0 E - 0 7
D a y _ i n t_ z @ 8 1 . 1 1 9 E - 0 5 5 . 0 8 5 E - 0 7 3 . 5 5 9 E - 0 1 2 . 8 6 6 E - 0 3 3 . 9 7 5 E - 0 6 1 . 8 0 8 E - 0 7
D a y _ i n t_ z @ 9 1 . 2 9 5 E - 0 5 4 . 2 4 3 E - 0 7 3 . 2 2 1 E - 0 1 2 . 5 7 8 E - 0 3 4 . 1 6 3 E - 0 6 1 . 3 3 1 E - 0 7
D a y _ i n t_ z @ 1 0 1 . 0 2 2 E - 0 5 4 . 2 8 3 E - 0 7 5 . 9 6 2 E - 0 1 8 . 1 8 8 E - 0 3 6 . 1 2 5 E - 0 6 2 . 9 8 9 E - 0 7
D a y _ i n t_ z @ 1 1 9 . 1 1 2 E - 0 6 2 . 8 6 8 E - 0 7 6 . 1 2 8 E - 0 1 6 . 4 1 1 E - 0 3 5 . 5 8 3 E - 0 6 1 . 7 5 4 E - 0 7
D a y _ i n t_ z @ 1 2 9 . 4 1 1 E - 0 6 2 . 0 0 0 E - 0 7 7 . 1 4 9 E - 0 1 1 . 7 3 1 E - 0 3 6 . 7 2 6 E - 0 6 1 . 4 3 0 E - 0 7
D a y _ i n t_ z @ 1 3 9 . 0 8 2 E - 0 6 3 . 4 0 3 E - 0 7 6 . 6 4 9 E - 0 1 8 . 8 4 9 E - 0 3 6 . 0 1 4 E - 0 6 2 . 2 6 5 E - 0 7
D a y _ i n t_ z @ 1 4 1 . 1 0 6 E - 0 5 1 . 4 0 0 E - 0 6 6 . 4 1 9 E - 0 1 5 . 3 9 9 E - 0 3 7 . 1 4 3 E - 0 6 9 . 3 6 5 E - 0 7
D a y _ i n t_ z @ 1 5 9 . 6 6 9 E - 0 6 4 . 3 0 1 E - 0 7 5 . 8 2 6 E - 0 1 4 . 5 8 8 E - 0 3 5 . 6 4 1 E - 0 6 2 . 5 1 0 E - 0 7
D a y _ i n t_ z @ 1 6 1 . 3 7 1 E - 0 5 6 . 1 0 4 E - 0 7 1 . 4 9 6 E + 0 0 2 . 3 3 1 E - 0 2 2 . 0 5 1 E - 0 5 9 . 4 2 3 E - 0 7
D a y _ i n t_ z @ 1 7 9 . 9 8 3 E - 0 6 3 . 5 1 4 E - 0 7 5 . 2 6 6 E - 0 1 6 . 0 3 5 E - 0 3 5 . 2 5 2 E - 0 6 1 . 8 4 7 E - 0 7
D a y _ i n t_ z @ 1 8 7 . 3 9 3 E - 0 6 5 . 4 3 8 E - 0 7 1 . 4 8 9 E + 0 0 1 . 5 8 8 E - 0 2 1 . 0 9 1 E - 0 5 8 . 1 5 3 E - 0 7
D a y _ i n t_ z @ 1 9 1 . 0 8 0 E - 0 5 3 . 9 9 6 E - 0 7 4 . 6 2 5 E - 0 1 1 . 6 9 6 E - 0 3 4 . 9 9 3 E - 0 6 1 . 8 4 7 E - 0 7
D a y _ i n t_ z @ 2 1 9 . 1 2 9 E - 0 6 2 . 1 8 7 E - 0 7 6 . 3 2 7 E - 0 1 2 . 6 6 2 E - 0 3 5 . 7 8 1 E - 0 6 1 . 3 8 3 E - 0 7
D a y _ i n t_ z @ 2 2 1 . 0 2 6 E - 0 5 3 . 0 6 3 E - 0 7 5 . 6 2 9 E - 0 1 9 . 4 3 8 E - 0 3 5 . 7 9 7 E - 0 6 2 . 1 5 0 E - 0 7
D a y _ i n t_ z @ 2 3 9 . 8 5 4 E - 0 6 3 . 9 0 5 E - 0 7 4 . 5 9 4 E - 0 1 1 . 7 3 3 E - 0 3 4 . 5 2 8 E - 0 6 1 . 7 9 5 E - 0 7
 
48 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively. 
 
S a m pl e 2 4 6 . 0 2 9 / 2 4 6 . 0 2 9 / U  O / U  O / 2 4 6 . 0 2 9 / 2 4 6 . 0 2 9 /
U  O U  O Th  O Th  O Th  O Th  O
1  s.e . 1  s.e . 1  s.e .
D a y _ i n t_ z @ 1 8 . 7 7 4 E - 0 6 1 . 5 2 1 E - 0 7 1 . 4 5 9 E + 0 0 1 . 1 4 5 E - 0 2 1 . 2 8 2 E - 0 5 2 . 4 5 0 E - 0 7
D a y _ i n t_ z @ 2 9 . 9 5 9 E - 0 6 3 . 7 2 4 E - 0 7 6 . 5 7 2 E - 0 1 1 . 1 7 7 E - 0 2 6 . 5 2 7 E - 0 6 2 . 4 4 1 E - 0 7
D a y _ i n t_ z @ 3 8 . 3 7 2 E - 0 6 3 . 9 5 3 E - 0 7 5 . 9 7 2 E - 0 1 6 . 1 1 4 E - 0 3 5 . 0 0 2 E - 0 6 2 . 3 6 5 E - 0 7
D a y _ i n t_ z @ 4 1 . 0 3 0 E - 0 5 4 . 4 8 4 E - 0 7 5 . 5 0 8 E - 0 1 6 . 9 4 6 E - 0 3 5 . 6 7 0 E - 0 6 2 . 4 8 0 E - 0 7
D a y _ i n t_ z @ 5 9 . 5 1 4 E - 0 6 4 . 7 1 7 E - 0 7 5 . 4 0 0 E - 0 1 1 . 9 1 3 E - 0 2 5 . 0 6 8 E - 0 6 2 . 4 9 3 E - 0 7
D a y _ i n t_ z @ 6 1 . 0 7 4 E - 0 5 3 . 5 0 9 E - 0 7 4 . 9 0 2 E - 0 1 4 . 0 3 2 E - 0 3 5 . 2 6 4 E - 0 6 1 . 7 2 2 E - 0 7
D a y _ i n t_ z @ 7 1 . 1 9 8 E - 0 5 5 . 9 6 0 E - 0 7 2 . 6 9 5 E - 0 1 2 . 4 4 1 E - 0 3 3 . 2 1 9 E - 0 6 1 . 6 0 4 E - 0 7
D a y _ i n t_ z @ 8 1 . 0 9 1 E - 0 5 5 . 0 9 0 E - 0 7 3 . 5 5 9 E - 0 1 2 . 8 6 6 E - 0 3 3 . 8 7 3 E - 0 6 1 . 8 1 1 E - 0 7
D a y _ i n t_ z @ 9 1 . 2 7 3 E - 0 5 4 . 1 1 0 E - 0 7 3 . 2 2 1 E - 0 1 2 . 5 7 8 E - 0 3 4 . 0 9 1 E - 0 6 1 . 2 8 5 E - 0 7
D a y _ i n t_ z @ 1 0 1 . 0 1 5 E - 0 5 4 . 0 9 8 E - 0 7 5 . 9 6 2 E - 0 1 8 . 1 8 8 E - 0 3 6 . 0 8 3 E - 0 6 2 . 8 9 0 E - 0 7
D a y _ i n t_ z @ 1 1 9 . 1 1 6 E - 0 6 2 . 7 9 7 E - 0 7 6 . 1 2 8 E - 0 1 6 . 4 1 1 E - 0 3 5 . 5 8 4 E - 0 6 1 . 7 1 1 E - 0 7
D a y _ i n t_ z @ 1 2 9 . 3 4 1 E - 0 6 1 . 9 8 8 E - 0 7 7 . 1 4 9 E - 0 1 1 . 7 3 1 E - 0 3 6 . 6 7 6 E - 0 6 1 . 4 2 1 E - 0 7
D a y _ i n t_ z @ 1 3 8 . 9 8 3 E - 0 6 3 . 3 5 1 E - 0 7 6 . 6 4 9 E - 0 1 8 . 8 4 9 E - 0 3 5 . 9 5 4 E - 0 6 2 . 2 2 5 E - 0 7
D a y _ i n t_ z @ 1 4 1 . 0 9 4 E - 0 5 1 . 3 9 8 E - 0 6 6 . 4 1 9 E - 0 1 5 . 3 9 9 E - 0 3 7 . 0 6 5 E - 0 6 9 . 3 5 6 E - 0 7
D a y _ i n t_ z @ 1 5 9 . 7 1 9 E - 0 6 4 . 1 4 6 E - 0 7 5 . 8 2 6 E - 0 1 4 . 5 8 8 E - 0 3 5 . 6 6 8 E - 0 6 2 . 4 2 4 E - 0 7
D a y _ i n t_ z @ 1 6 1 . 3 4 2 E - 0 5 6 . 0 7 9 E - 0 7 1 . 4 9 6 E + 0 0 2 . 3 3 1 E - 0 2 2 . 0 0 9 E - 0 5 9 . 3 8 0 E - 0 7
D a y _ i n t_ z @ 1 7 9 . 8 8 1 E - 0 6 3 . 4 5 6 E - 0 7 5 . 2 6 6 E - 0 1 6 . 0 3 5 E - 0 3 5 . 1 9 6 E - 0 6 1 . 8 2 0 E - 0 7
D a y _ i n t_ z @ 1 8 7 . 3 6 6 E - 0 6 5 . 1 3 1 E - 0 7 1 . 4 8 9 E + 0 0 1 . 5 8 8 E - 0 2 1 . 0 8 9 E - 0 5 7 . 6 5 5 E - 0 7
D a y _ i n t_ z @ 1 9 1 . 0 7 4 E - 0 5 3 . 9 3 9 E - 0 7 4 . 6 2 5 E - 0 1 1 . 6 9 6 E - 0 3 4 . 9 6 7 E - 0 6 1 . 8 2 1 E - 0 7
D a y _ i n t_ z @ 2 1 9 . 0 3 1 E - 0 6 2 . 1 7 0 E - 0 7 6 . 3 2 7 E - 0 1 2 . 6 6 2 E - 0 3 5 . 7 1 9 E - 0 6 1 . 3 7 3 E - 0 7
D a y _ i n t_ z @ 2 2 9 . 7 9 9 E - 0 6 3 . 1 1 4 E - 0 7 5 . 6 2 9 E - 0 1 9 . 4 3 8 E - 0 3 5 . 5 4 0 E - 0 6 2 . 1 7 1 E - 0 7
D a y _ i n t_ z @ 2 3 9 . 0 3 9 E - 0 6 3 . 8 8 3 E - 0 7 4 . 5 9 4 E - 0 1 1 . 7 3 3 E - 0 3 4 . 1 5 2 E - 0 6 1 . 7 8 4 E - 0 7
( a v e r a g e  2 4 6 . 3  +  2 4 4 . 0 3 8 )
 
49 
 
Table 2 continued   
Raw data for Dayingshan zircon rims and cores collected from SIMS analyses.  1 s.e. is the standard error, which represents 
measurement uncertainty.  Background is measured at 246.3 and 244.038, respectively. 
 
S a m pl e 2 4 6 . 0 2 9 / 2 4 6 . 0 2 9 / U  O / U  O / 2 4 6 . 0 2 9 / 2 4 6 . 0 2 9 /
U  O U  O Th  O Th  O Th  O Th  O
1  s.e . 1  s.e . 1  s.e .
D a y _ i n t_ z @ 1 8 . 8 1 6 E - 0 6 1 . 5 2 8 E - 0 7 1 . 4 5 9 E + 0 0 1 . 1 4 5 E - 0 2 1 . 2 8 8 E - 0 5 2 . 4 6 2 E - 0 7
D a y _ i n t_ z @ 2 1 . 0 0 1 E - 0 5 3 . 7 4 2 E - 0 7 6 . 5 7 2 E - 0 1 1 . 1 7 7 E - 0 2 6 . 5 5 8 E - 0 6 2 . 4 5 2 E - 0 7
D a y _ i n t_ z @ 3 8 . 4 1 2 E - 0 6 3 . 9 7 2 E - 0 7 5 . 9 7 2 E - 0 1 6 . 1 1 4 E - 0 3 5 . 0 2 6 E - 0 6 2 . 3 7 6 E - 0 7
D a y _ i n t_ z @ 4 1 . 0 3 5 E - 0 5 4 . 5 0 5 E - 0 7 5 . 5 0 8 E - 0 1 6 . 9 4 6 E - 0 3 5 . 6 9 7 E - 0 6 2 . 4 9 1 E - 0 7
D a y _ i n t_ z @ 5 9 . 5 5 9 E - 0 6 4 . 7 3 9 E - 0 7 5 . 4 0 0 E - 0 1 1 . 9 1 3 E - 0 2 5 . 0 9 2 E - 0 6 2 . 5 0 5 E - 0 7
D a y _ i n t_ z @ 6 1 . 0 7 9 E - 0 5 3 . 5 2 6 E - 0 7 4 . 9 0 2 E - 0 1 4 . 0 3 2 E - 0 3 5 . 2 8 9 E - 0 6 1 . 7 3 0 E - 0 7
D a y _ i n t_ z @ 7 1 . 2 0 4 E - 0 5 5 . 9 8 9 E - 0 7 2 . 6 9 5 E - 0 1 2 . 4 4 1 E - 0 3 3 . 2 3 5 E - 0 6 1 . 6 1 1 E - 0 7
D a y _ i n t_ z @ 8 1 . 0 9 6 E - 0 5 5 . 1 1 4 E - 0 7 3 . 5 5 9 E - 0 1 2 . 8 6 6 E - 0 3 3 . 8 9 1 E - 0 6 1 . 8 2 0 E - 0 7
D a y _ i n t_ z @ 9 1 . 2 7 9 E - 0 5 4 . 1 2 9 E - 0 7 3 . 2 2 1 E - 0 1 2 . 5 7 8 E - 0 3 4 . 1 1 0 E - 0 6 1 . 2 9 1 E - 0 7
D a y _ i n t_ z @ 1 0 1 . 0 2 0 E - 0 5 4 . 1 1 7 E - 0 7 5 . 9 6 2 E - 0 1 8 . 1 8 8 E - 0 3 6 . 1 1 2 E - 0 6 2 . 9 0 4 E - 0 7
D a y _ i n t_ z @ 1 1 9 . 1 5 9 E - 0 6 2 . 8 1 0 E - 0 7 6 . 1 2 8 E - 0 1 6 . 4 1 1 E - 0 3 5 . 6 1 0 E - 0 6 1 . 7 1 9 E - 0 7
D a y _ i n t_ z @ 1 2 9 . 3 8 5 E - 0 6 1 . 9 9 7 E - 0 7 7 . 1 4 9 E - 0 1 1 . 7 3 1 E - 0 3 6 . 7 0 8 E - 0 6 1 . 4 2 8 E - 0 7
D a y _ i n t_ z @ 1 3 9 . 0 2 5 E - 0 6 3 . 3 6 7 E - 0 7 6 . 6 4 9 E - 0 1 8 . 8 4 9 E - 0 3 5 . 9 8 2 E - 0 6 2 . 2 3 6 E - 0 7
D a y _ i n t_ z @ 1 4 1 . 0 9 9 E - 0 5 1 . 4 0 5 E - 0 6 6 . 4 1 9 E - 0 1 5 . 3 9 9 E - 0 3 7 . 0 9 9 E - 0 6 9 . 4 0 1 E - 0 7
D a y _ i n t_ z @ 1 5 9 . 7 6 6 E - 0 6 4 . 1 6 6 E - 0 7 5 . 8 2 6 E - 0 1 4 . 5 8 8 E - 0 3 5 . 6 9 5 E - 0 6 2 . 4 3 6 E - 0 7
D a y _ i n t_ z @ 1 6 1 . 3 4 8 E - 0 5 6 . 1 0 8 E - 0 7 1 . 4 9 6 E + 0 0 2 . 3 3 1 E - 0 2 2 . 0 1 8 E - 0 5 9 . 4 2 4 E - 0 7
D a y _ i n t_ z @ 1 7 9 . 9 2 8 E - 0 6 3 . 4 7 3 E - 0 7 5 . 2 6 6 E - 0 1 6 . 0 3 5 E - 0 3 5 . 2 2 1 E - 0 6 1 . 8 2 8 E - 0 7
D a y _ i n t_ z @ 1 8 7 . 4 0 1 E - 0 6 5 . 1 5 5 E - 0 7 1 . 4 8 9 E + 0 0 1 . 5 8 8 E - 0 2 1 . 0 9 4 E - 0 5 7 . 6 9 1 E - 0 7
D a y _ i n t_ z @ 1 9 1 . 0 7 9 E - 0 5 3 . 9 5 8 E - 0 7 4 . 6 2 5 E - 0 1 1 . 6 9 6 E - 0 3 4 . 9 9 0 E - 0 6 1 . 8 3 0 E - 0 7
D a y _ i n t_ z @ 2 1 9 . 0 7 4 E - 0 6 2 . 1 8 0 E - 0 7 6 . 3 2 7 E - 0 1 2 . 6 6 2 E - 0 3 5 . 7 4 6 E - 0 6 1 . 3 7 9 E - 0 7
D a y _ i n t_ z @ 2 2 9 . 8 4 5 E - 0 6 3 . 1 2 9 E - 0 7 5 . 6 2 9 E - 0 1 9 . 4 3 8 E - 0 3 5 . 5 6 7 E - 0 6 2 . 1 8 1 E - 0 7
D a y _ i n t_ z @ 2 3 9 . 0 8 2 E - 0 6 3 . 9 0 1 E - 0 7 4 . 5 9 4 E - 0 1 1 . 7 3 3 E - 0 3 4 . 1 7 2 E - 0 6 1 . 7 9 3 E - 0 7
g a i n  c o r r e c te d  ( a v e r a g e  g a i n  1 . 0 0 5 E + 0 0 )
 
50 
 
a concentrated beam.  The ion beam then travels through the primary ion column before 
contacting the target sample.  Upon contact, a small percentage of target atoms become  
ionized (typically < 10%) (Stern, 2009).  These secondary ions then pass through the 
secondary ion column into a mass spectrometer containing an electrostatic analyzer 
(ESA) and an electromagnet.  The ESA is used to deflect ions based on their energy 
levels, while the electromagnet deflects particles based on their masses.  Both instruments 
serve the purpose of increasing the mass resolution.  Entrance and exit slits are located 
before and after the analyzers, and are adjusted accordingly in order to obtain the highest 
mass resolution.  The last step is to measure and count the secondary ions.  Several 
different secondary ion detection measures may be used according to need.  These 
include an ion counting electron multiplier, Faraday cups, and ion image detectors.  
Figure 13 is a simplified diagram showing these fundamental components of SIMS. 
 Individual spots on zircons are targeted using Customizable Ion Probe Software 
(CIPS).  Each component of SIMS is monitored and adjusted using CIPS.  Individual 
spots can be targeted by hand due to a magnified view of zircon surfaces in reflected 
light.  The Cameca ims 1270 is also able to image ions, which is useful for targeting 
specific regions of the sample based on composition.  After selecting the placement of 
each spot, the zircons are sputtered in series, with each zircon taking ~20 minutes to 
analyze.  Once the sputtering process is complete, the data obtained is transferred into a 
Microsoft Excel spreadsheet.  An Excel spreadsheet is necessary in order to use the 
program Isoplot (Ludwig, 2003), which provides the capability to plot radiogenic isotope 
data.  An Excel spreadsheet also presents the data in a more reader-friendly format, 
allowing for easier data interpretation.      
51 
 
   
 
 
 
 
 
 
 
Fig. 13.  Diagram depicting the fundamental components of a SIMS instrument (After 
Stern, 2009). 
 
 
 
 
 
 
 
 
52 
 
 Erroneous data may be recorded from SIMS due to counting errors, relative 
sensitivity factor (RSF) uncertainties, primary beam instabilities, zircon surface 
topography, or changes in surface conductivity with depth (Schmitt, 2009).  RSF involves 
the measuring of faint isotopes adjacent to abundant ones.  Systematic errors such as 
matrix effects, drift in detector gain, and detector non-linearity may also occur (Schmitt, 
2009).  These problems can typically be held in check by periodically measuring 
standards while measurements for zircons of unknown age are being made, and by 
closely monitoring SIMS instrumentation from the control console.  Significant Th-U 
fractionation is absent in zircon, and therefore is not a factor.  The most prevalent error in 
Quaternary zircon measurements is counting errors due to low signals (Schmitt, 2009).  
Great care was taken to ensure that these errors did not occur. 
53 
 
RESULTS 
Dayingshan Whole-Rock Major and Trace Element Analysis 
 Whole-rock analysis of rock sample YTC9724-5 from Dayingshan (Zou, 2010) 
yielded similar results to data from Maanshan volcano (Fig. 2) (Zou et al., 2010).  
The major and trace element concentrations can be seen in Table 3.  Of particular 
interest is the high Zr concentration of 303 ppm.  High Zr concentrations indicate a 
more silicic magma.  It is also important to note that SiO2, FeO and MgO weight 
percentages of the Dayingshan sample are indicative of a calc-alkaline suite.  These 
concentrations, along with those from several other rocks collected from 
Dayingshan (Zou, 2010; Wang, F. et al., 2006; Zhao and Fan, 2010) were plotted on a 
FeO/MgO vs. SiO2 plot, and demonstrate an overall calc-alkaline trend (Fig. 14).  
  Calc-alkaline rocks typically show enrichment in silica and alkalies, low 
enrichment in iron, and typify subduction zones.  YTC9724-5 whole-rock analysis 
also yielded high K.  High-K calc-alkaline rocks tend to develop on increasingly 
thicker continental crust (Best, 2003).   
 Calc-alkaline rocks are typically enriched in light rare earth elements 
(LREE?s), and show a negative slope on an REE plot (Fig. 15).  Plotted trace element 
patterns in calc-alkaline rocks are commonly irregular, and show enrichment in the 
more incompatible elements, such as Rb, and depletion in elements with high field 
strengths, such as Nb and Ta (Best, 2003).  Figure 16 is a spider diagram from the 
54 
 
 
 
 
 
Table 3   
Major and trace element concentrations from Dayingshan whole-rock analysis of sample  
YTC9724-5. 
 
 
55 
 
 
 
Fig. 14.  FeO/MgO vs. SiO2 plot demonstrating an overall calc-alkaline trend in 
Dayingshan samples.  The dividing line is defined by Irvine and Barager (1971).  Data 
points were collected from Zou (2010), Wang, F. et al. (2006), and Zhao and Fan (2010).  
56 
 
 
Fig. 15.  REE plot of sample YTC9724-5 from Dayingshan and sample MA02 from 
Maanshan (Zou et al., 2010).  The vertical axis is normalized using average abundances in 
chondritic meteorites.  The negative slope indicates enrichment in LREE?s. 
57 
 
 
Fig. 16.  Spider diagram of Dayingshan (YTC9724-5) and Maanshan (MA02) (Zou et al., 2010) trace 
elements.  The vertical axis is normalized using estimated primitive mantle.  A spiked, irregular pattern with 
an overall negative slope is indicative of a calc-alkaline sample. 
58 
 
Dayingshan sample, which demonstrates these relationships.  This type of pattern is 
believed to reflect magma generation involving hydrous fluids in the mantle source 
overlying the downgoing lithospheric slab (Best, 2003).  Both the REE diagram and 
spider diagram must be normalized in order to smooth out ups and downs due to 
the greater abundances of even atomic numbers over odd atomic numbers (Oddo-
Harkins rule).  Referencing primitive materials also makes measurements easier to 
judge than absolute concentrations.  The REE plot (Fig. 15) is normalized using 
element concentrations in average chondritic meteorites, while the spider diagram 
(Fig. 16) is normalized using average primitive mantle.  
 The Dayingshan rock sample is metaluminous, with an alumina saturation 
index (ASI) molecular ratio (Al2O3/(CaO+K2O+Na2O)) of 0.91 and Al2O3/(K2O+Na2O) 
of 1.63.  Metaluminous rocks are defined as having molecular Al2O3 greater than 
(K2O+Na2O) but less than (CaO+K2O+Na2O).  Metaluminous samples are typically 
felsic, and the deficiency in alumina is accommodated in hornblende and biotite.  A 
metaluminous composition, coupled with high Zr concentrations, would likely 
stabilize any entrained zircon xenocrysts if they were present (Zou et al., 2010).  
Polished Zircon Core Ages 
 Zircon cores were measured by SIMS to attain the oldest ages of the minerals.  
Dayingshan zircons did not show well-developed growth-zoning, however they did 
provide enough surface area for SIMS analysis.  Selected zircon 
cathodoluminescence images are shown in Figure 17.  Twenty-two polished zircon 
cores were measured (Table 4), with 21 grains yielding an apparent U/Th isochron  
 
59 
 
 
 
 
 
 
Fig. 17.  Cathodoluminescence images of sample Day-int4 and Day-int1 with SIMS 
crater spots.  Growth zoning is not well-developed in these zircons. 
 
 
 
 
60 
 
Table 4   
U/Th isotope data, concentrations, and ages for Dayingshan zircon cores as measured by SIMS.  Ages were calculated using 
Isoplot (Ludwig, 2003).  1s is the standard error and is a measurement of uncertainty. 
 
S a m p l e (
238
U/
232
T h ) 1s (
230
T h /
232
T h ) 1s U  ( p p m ) T h  ( p p m ) T h / U D
T h / U
A g e  ( k a )  +  ( k a )  -  ( k a )
D a y - i n t1 1 . 3 2 6 0 . 0 2 5 2 . 3 8 4 0 . 0 4 6 2644 1929 0 . 7 3 0 . 0 7 8 3 . 6 3 . 8 - 3 . 7
D a y - i n t2 0 . 5 9 7 0 . 0 1 7 1 . 2 1 4 0 . 0 4 5 529 858 1 . 6 2 0 . 1 5 9 1 . 6 9 . 2 - 8 . 5
D a y - i n t3 0 . 5 4 3 0 . 0 1 1 0 . 9 3 0 . 0 4 4 395 704 1 . 7 8 0 . 1 7 6 2 . 2 6 . 6 - 6 . 3
D a y - i n t4 0 . 5 0 1 0 . 0 1 2 1 . 0 5 4 0 . 0 4 6 430 831 1 . 9 3 0 . 1 8 9 4 . 2 1 0 . 9 - 9 . 9
D a y - i n t5 0 . 4 9 1 0 . 0 2 3 0 . 9 4 3 0 . 0 4 6 369 727 1 . 9 7 0 . 1 9 7 6 . 1 1 0 . 9 - 9 . 9
D a y - i n t6 0 . 4 4 6 0 . 0 0 8 0 . 9 7 9 0 . 0 3 2 681 1479 2 . 1 7 0 . 2 1 1 0 0 . 1 9 . 3 - 8 . 6
D a y - i n t7 0 . 2 4 5 0 . 0 0 5 0 . 5 9 9 0 . 0 3 0 353 1396 3 . 9 5 0 . 3 7 9 8 . 6 1 9 . 8 - 1 6 . 7
D a y - i n t8 0 . 3 2 4 0 . 0 0 6 0 . 7 2 0 . 0 3 4 397 1186 2 . 9 9 0 . 2 8 8 9 . 5 1 3 . 1 - 1 1 . 7
D a y - i n t9 0 . 2 9 3 0 . 0 0 5 0 . 7 6 1 0 . 0 2 4 769 2543 3 . 3 1 0 . 3 1 1 3 6 . 4 1 8 . 1 - 1 5 . 5
D a y - i n t1 0 0 . 5 4 2 0 . 0 1 3 1 . 1 3 1 0 . 0 5 4 499 891 1 . 7 9 0 . 1 7 9 4 . 6 1 1 . 5 - 1 0 . 4
D a y - i n t1 1 0 . 5 5 7 0 . 0 1 2 1 . 0 3 9 0 . 0 3 2 753 1309 1 . 7 4 0 . 1 6 7 4 . 8 5 . 7 - 5 . 4
D a y - i n t1 2 0 . 6 5 0 . 0 0 8 1 . 2 4 2 0 . 0 2 6 1377 2051 1 . 4 9 0 . 1 4 8 2 . 4 4 . 1 - 3 . 9
D a y - i n t1 3 0 . 6 0 4 0 . 0 1 4 1 . 1 0 7 0 . 0 4 1 509 815 1 . 6 0 0 . 1 5 7 4 . 2 6 . 6 - 6 . 2
D a y - i n t1 4 0 . 5 8 3 0 . 0 1 1 1 . 3 1 4 0 . 1 7 4 496 823 1 . 6 6 0 . 1 6 1 1 4 . 6 4 3 . 5 - 3 1 . 0
D a y - i n t1 5 0 . 5 3 0 . 0 1 1 . 0 5 4 0 . 0 4 5 395 721 1 . 8 3 0 . 1 7 8 4 . 6 8 . 7 - 8 . 1
D a y - i n t1 6 1 . 3 6 0 . 0 3 6 3 . 7 3 6 0 . 1 7 4 231 165 0 . 7 1 0 . 0 7 2 1 6 . 3 4 9 . 6 - 3 4 . 0
D a y - i n t1 7 0 . 4 7 9 0 . 0 1 1 0 . 9 6 6 0 . 0 3 4 510 1030 2 . 0 2 0 . 1 9 8 4 . 3 7 . 8 - 7 . 3
D a y - i n t1 8 1 . 3 5 4 0 . 0 2 9 2 . 0 2 5 0 . 1 4 2 266 190 0 . 7 2 0 . 0 7 6 1 . 7 7 . 5 - 7 . 0
D a y - i n t1 9 0 . 4 2 0 . 0 0 6 0 . 9 2 4 0 . 0 3 4 507 1168 2 . 3 0 0 . 2 2 9 8 . 0 9 . 9 - 9 . 0
D a y - i n t2 0 0 . 5 7 5 0 . 0 0 9 1 . 0 6 4 0 . 0 2 6 1233 2074 1 . 6 8 0 . 1 6 7 4 . 4 4 . 2 - 4 . 1
D a y - i n t2 1 0 . 5 1 2 0 . 0 1 4 1 . 0 3 0 . 0 4 0 700 1325 1 . 8 9 0 . 1 8 8 5 . 8 9 . 0 - 8 . 3
D a y - i n t2 2 0 . 4 1 8 0 . 0 0 6 0 . 7 7 2 0 . 0 3 3 405 939 2 . 3 2 0 . 2 2 6 4 . 7 6 . 9 - 6 . 5
 
 
 
61 
 
 
Fig. 18.  U/Th isochron plot for zircon cores from Dayingshan.  Chart was constructed and ages were determined using Isoplot             
(Ludwig, 2003). 
62 
 
age of 87.5 ? 6.5 ka (Fig. 18), with a mean square of weighted deviates (MSWD) of 
3.7.  This data is similar to a calculated age of 83.5 ? 9 ka for interiors of Maanshan 
zircons (Zou et al., 2010).  Sample Day-int16 was disregarded due to an inherently 
low U ppm.  The MSWD is essentially an expression of scatter, and is used to infer 
how many zircon populations are present.  Generally, an MSWD of <2.5 is 
considered to define an isochron (Brooks et al., 1972).  While an MSWD of 3.7 is 
higher than this cutoff, a mixture modeling chart, based on the probability density 
function, of U/Th ages of Dayingshan zircon interiors (Fig. 19) shows a single mode 
of zircons.  This is interpreted as representing a likely single population of zircons.         
 
Unpolished Zircon Rim Ages 
 Because the outer rims of Dayingshan zircons were smaller than the typical 
beam spot of 25 ?m, shallow (< 3 ?m) depth profiling analysis was used.  Depth 
profiling allows for specific targeting of the surface of natural zircon crystal faces.  
U/Th ages of 17 unpolished zircon grains were measured (Table 5).  One of these 
zircon measurements was disregarded due to high background readings.  The U/Th 
measured ages of the zircon rims is 58 ? 13 ka, with a MSWD of 1.8 (Fig. 20).  This 
age data is similar to the calculated age of 53.6 ? 5 ka by Zou et al. (2010) of 
unpolished zircons from Maanshan volcano.   
 
Comparison of Core and Rim Ages 
 Calculated core ages (87.5 ? 6.5 ka) are significantly older than the rim ages 
(58 ? 13 ka), representing at least two different magmatic events.  This older  
63 
 
 
Fig. 19.  Mixture modeling plot of zircon core ages from Dayingshan produced using the probability density function from Isoplot 
(Ludwig, 2003).  
64 
 
 
 
Table 5   
U/Th isotope data, concentrations and ages for Dayingshan zircon rims as measured by SIMS.  Ages were calculate using Isoplot 
(Ludwig, 2003).  1s is the standard error and is a measurement of uncertainty. 
 
Z i r c o n  S a m p l e (
238
U/
232
T h ) 1s (
230
T h /
232
T h ) 1s U  ( p p m ) T h  ( p p m ) T h / U D
T h / U
A g e  ( k a )  +  ( k a )  -  ( k a )
D a y - r i m1 1 . 4 2 0 0 . 0 2 0 3 . 3 6 0 0 . 2 1 0 988 674 0 . 6 8 0 . 0 6 1 4 4 . 8 2 3 . 6 - 1 9 . 4
D a y - r i m2 0 . 5 0 2 0 . 0 1 5 1 . 0 4 5 0 . 0 3 6 924 1781 1 . 9 3 0 . 1 8 9 4 . 2 9 . 4 - 8 . 7
D a y - r i m3 0 . 5 9 5 0 . 0 1 2 1 . 2 2 5 0 . 0 5 8 371 604 1 . 6 3 0 . 1 5 9 6 . 1 1 1 . 0 - 1 0 . 0
D a y - r i m4 0 . 7 6 8 0 . 0 1 3 1 . 6 1 7 0 . 1 1 7 415 522 1 . 2 6 0 . 1 2 1 0 5 . 6 1 7 . 5 - 1 5 . 1
D a y - r i m5 1 . 0 0 8 0 . 0 2 8 1 . 5 9 3 0 . 0 5 4 732 703 0 . 9 6 0 . 0 9 6 5 . 2 4 . 7 - 4 . 5
D a y - r i m6 0 . 5 3 8 0 . 0 0 8 1 . 0 7 5 0 . 0 3 5 622 1119 1 . 8 0 0 . 1 7 8 7 . 9 6 . 8 - 6 . 4
D a y - r i m7 0 . 2 8 0 0 . 0 0 7 0 . 7 5 9 0 . 0 5 3 266 921 3 . 4 6 0 . 3 3 1 6 3 . 6 5 9 . 5 - 3 8 . 3
D a y - r i m8 0 . 5 6 6 0 . 0 2 4 1 . 1 3 5 0 . 0 5 4 450 770 1 . 7 1 0 . 1 6 8 9 . 8 1 2 . 0 - 1 0 . 8
D a y - r i m9 0 . 4 4 9 0 . 0 0 8 1 . 0 1 7 0 . 0 3 3 660 1422 2 . 1 5 0 . 2 0 1 1 0 . 9 1 0 . 4 - 9 . 5
D a y - r i m1 0 0 . 7 5 7 0 . 0 2 0 1 . 3 6 4 0 . 0 6 4 545 697 1 . 2 8 0 . 1 2 7 7 . 7 7 . 9 - 7 . 4
D a y - r i m1 1 0 . 8 8 7 0 . 0 1 8 1 . 7 3 1 0 . 0 7 0 541 590 1 . 0 9 0 . 1 0 9 2 . 9 8 . 2 - 7 . 6
D a y - r i m1 2 0 . 6 9 9 0 . 0 1 0 1 . 3 7 4 0 . 0 3 8 981 1358 1 . 3 8 0 . 1 3 9 0 . 4 5 . 7 - 5 . 4
D a y - r i m1 3 0 . 8 2 9 0 . 0 1 5 1 . 3 9 2 0 . 0 4 4 1050 1226 1 . 1 7 0 . 1 1 6 9 . 6 4 . 5 - 4 . 3
D a y - r i m1 4 0 . 6 5 6 0 . 0 1 0 1 . 3 4 9 0 . 0 6 2 591 873 1 . 4 8 0 . 1 4 9 7 . 9 1 0 . 3 - 9 . 4
D a y - r i m1 5 0 . 5 7 3 0 . 0 1 7 1 . 1 9 2 0 . 0 6 2 484 817 1 . 6 9 0 . 1 6 9 7 . 4 1 3 . 0 - 1 1 . 6
D a y - r i m1 6 0 . 8 5 1 0 . 0 1 6 1 . 8 3 7 0 . 0 9 5 328 373 1 . 1 4 0 . 1 1 1 1 2 . 9 1 3 . 7 - 1 2 . 2
D a y - r i m1 7 0 . 4 5 8 0 . 0 0 8 0 . 9 7 5 0 . 0 3 3 908 1921 2 . 1 1 0 . 2 0 9 6 . 5 8 . 7 - 8 . 1
 
65 
 
 
Fig. 20.  U/Th isochron plot for zircon rims from Dayingshan using shallow depth profiling.  Chart was constructed and ages were 
determined using Isoplot (Ludwig, 2003). 
66 
 
population is not old enough to be incorporated xenocrysts from basement rock, 
however it may represent zircons that have been remobilized from an earlier 
magmatic episode (Zou et al., 2010).  These zircons could be considered antecrysts, 
in that they grew from predecessor magmas left over in the magma chamber.  This 
could be tested with U/Th dating of rocks from previous Quaternary eruptive events 
from Dayingshan.  
 
Zircon Saturation  
 Whether the melt was saturated with respect to zircon is important when 
trying to interpret possible zircon inheritance from country rock.  Zircon saturation 
is a function of both magma composition and temperature, and is defined by the 
equation: 
 
 
where  is the concentration ratio of Zr in zircon to Zr in the melt, M 
represents the melt composition ((Na+K+2Ca)/(Al?Si)), and T is the temperature in 
Kelvin.  This study uses zircon saturation as a means to deduce zircon inheritance in 
the system.  According to major element compositions in Dayingshan YTC9724-5,   
M = 1.87.  An estimated temperature of 750?C is used based on Ti-in-zircon 
geothermometry from Maanshan (Zou et al., 2010).  Using these two variables, the 
Zr concentration needed to saturate the melt is 156 ppm.  Because whole-rock 
analysis yielded a Zr concentration of 303 ppm, and only 156 ppm is needed to 
67 
 
saturate the melt, we can infer that the melt was saturated in Zr.  Under these 
saturated conditions, any inherited zircons from country rock would remain stable 
in the melt.  This knowledge, along with the fact that no zircons as old as the country 
rock have been found, provides evidence that there is no contamination from 
country rock. 
68 
 
DISCUSSION  
Magma Chamber Storage Time 
 Storage of magma in magma chambers is often poorly understood because it 
is difficult to isotopically date materials recording the duration.  A determination of 
magma storage time in the Tengchong volcanic field is important for several 
reasons.  A better understanding of magma chamber processes could provide 
valuable insights into the ascent and storage of magma, especially in this unique 
volcanic environment.  This information could prove valuable to the many people 
who live in close proximity to the active volcanoes.  In large part, industry and 
tourism attract people into areas within active geothermal fields (Wei et al., 2003).  
Figure 21 is a map showing the distribution of some of the major cities and villages 
in the Tengchong volcanic field.  In addition to industry and tourism, fertile volcanic 
soil for growing crops is another factor leading to increased population in this area.    
 Basement rocks to the Tengchong volcanoes are mostly granites with ages 
~5.5 Ma (Ji, 1998).  Other country rocks in the area include Paleozoic gneisses and 
Carboniferous sandstones.  Since all these rocks are significantly older than 
measured Dayingshan zircon ages (58 and 87.5 ka), and because inherited zircons 
would have been stable in the melt if they were present, it is safe to assume that 
there are no inherited zircons from country rock.  Therefore, the zircons present 
must have formed in the magma chamber prior to eruption.  We can infer magma 
69 
 
 
 
Fig. 21.  Satellite image of the southern portion of the Tengchong volcanic field showing the distribution of some of the major cities 
and villages in the region.  Maanshan and Dayingshan are outlined in red.  Major cities and villages, including Tengchong (population 
620,000), are outlined in yellow.  Map produced using Google Earth.    
Tengchong 
Dayingshan 
? 
Maanshan 
70 
 
chamber storage time by subtracting the volcanic eruption event that yielded the 
basaltic andesites from the calculated zircon ages.  Using an eruption age of ~10 ka 
(Zou et al., 2010), a magma chamber storage time of 48 ka is determined for zircon 
rims and 77.5 ka for zircon cores.          
 
Th/U Ratios  
 Dayingshan zircons have higher than average Th/U ratios for igneous 
zircons.  An average Th/U ratio for most igneous zircons is ~0.5, and typically 
ranges from 0.2 - 0.9 (Bindeman et al., 2006).  Unusually high Th/U ratios are often 
indicative of a continental crust component in the melt.  Dayingshan cores have an 
averageTh/U ratio of 1.92, and range from 0.71 ? 3.95.  Dayingshan rims have an 
average Th/U ratio of 1.58, and range from 0.68 ? 3.46.  Though the variation in 
Th/U ratios is high, zircon rims yielded only slightly lower ratios than zircon cores.  
A rimward decrease in Th/U ratios is indicative of fractionation during zircon 
growth (Zou et al., 2010).  Despite the slight difference in Th/U ratios, the similarity 
between core and rim ratios suggests the crystals share a closed-system evolution, 
implying that contamination in the magma system since the zircon core formation is 
minimal (Zou et al., 2010).    
 In order to determine if the high Th/U ratios in the Dayingshan zircons are a 
result of high Th/U ratios in the original melt, the mineral/melt partitioning 
coefficients (DTh/U) for the concentrations of Th and U must be determined.  DTh/U is 
the ratio of concentration of U and Th in a crystallizing zircon to concentration of 
these elements in the melt. DTh/U is calculated by the following equation: 
71 
 
 
  
 Using this equation, and a Th/U melt ratio of 10.6 determined from the 
isotope dilution method at National Taiwan University, the average DTh/U  is 0.18 ? 
0.07 for zircon cores and 0.15 ? 0.06 for zircon interiors.  Uncertainty for calculated 
DTh/U is large due to the large spread in Th/U ratios, however, DTh/U is fairly constant 
for most igneous rock compositions.  These DTh/U measurements are similar to an 
average DTh/U of 0.26 ? 0.16 for zircons from intermediate rocks (55-65 wt% SiO2), 
in spite of their high Th/U ratios that typically suggest a more felsic composition.  
Because of this, it is safe to assume that the high Th/U ratios in Dayingshan zircons 
were inherited from a high Th/U melt.   
 
Comparison of Dayingshan and Maanshan Data  
 Isotopic and trace element data accumulated from Dayingshan reinforces 
data from an earlier study of Maanshan by Zou et al. (2010).  Maanshan is another 
recently active volcano in the Tengchong volcanic field, and lies ~13 km to the south 
of Dayingshan (Fig. 2).  Similar SiO2 , K2O and Na2O contents (58.46, 3.40 and 3.79 
wt% in Maanshan; 62.24, 4.05 and 3.29 wt% in Dayingshan) indicate similar rock 
composition, and provide evidence for differentiation of the lavas.  Zr 
concentrations are also high in Maanshan (260 ppm) and Dayingshan (303 ppm).  
Because high SiO2 contents provide favorable conditions for zircon crystals to form, 
and Zr melt concentrations from both volcanoes are high, rocks contain abundant 
72 
 
amounts of zircon crystals.  Lavas from both volcanoes also have metaluminous 
compositions, with Maanshan (1.67) rocks showing a slightly higher 
Al2O3/(K2O+Na2O) value than Dayingshan (1.63).   
 Measured Maanshan Th/U ratios ranged from 0.65 to 5.1 for zircon interiors 
and 0.32 to 2.44 from zircon rims, which are unusually high for igneous zircons.  
These high ratios were also measured from Dayingshan (0.71 to 3.95 for zircon 
interiors and 0.68 to 3.46 for zircon rims).  Because higher Th/U ratios reflect a 
more enriched source, this is a strong indication for a melt with a crustal 
component.  One significant difference between Th/U measurements is that 
Maanshan zircon cores have two (young and old) populations while Dayingshan 
zircon cores have only one (old) age population.  The apparent lack of young zircon 
cores at Dayingshan might be due to limited sampling. 
 Age calculations also seem to correspond between the two volcanoes.  
Analysis of zircons from Maanshan recorded a bimodal population for zircon 
interiors, with calculated ages of 55 ? 7 ka for the younger population and 91 ? 6 ka 
for the older population.  Zircon rims recorded an age of 53.6 ? 5 ka.  Dayingshan 
zircon interior measurements yielded a unimodal age of 87.5 ? 6 ka, while zircon 
rim measurements yielded an age of 58 ? 13 ka.  The older age population from 
Maanshan zircon interiors is consistent with the age of Dayingshan zircon interiors, 
and Maanshan zircon rim ages are consistent with Dayingshan zircon rim ages.  This 
consistency further reaffirms the validity of the age data, and provides greater 
confidence in the capabilities of SIMS.  Better constraints on population ages could 
73 
 
be reinforced by future studies of Heikongshan volcano (Fig. 2), which lays ~10 km 
north of Dayingshan. 
 
Assessment of Magma Origins 
 Trace element data, along with Nd and Sr isotopic data from several studies 
(Zhu et al., 1983; Wang, F. et al., 2006; Zou et al., 2010), display enriched mantle 
characteristics.  Enriched signatures are indicative of a crustal element in the melt 
that could be introduced into the system in several different ways.  One way to 
potentially introduce a continental element is from continental contamination 
through assimilation of country rock.  This is an unlikely source due to the fact that 
none of the 60+ zircons dated between this study and Zou et al. (2010) have 
recorded ages as old as the country rocks in Tengchong.  Xenocrysts could not have 
re-dissolved into the magma because a melt saturated in Zr (303 ppm) and a 
metaluminous composition would stabilize any incorporated zircon xenocrysts.   
 With crustal contamination ruled out, the U-Th data in this study indicates 
continental subduction as a likely origin for the volcanism in the Tengchong volcanic 
field.  While it is clear that Indian plate subduction does not reach as far as the field 
(Wang & Long, 1998; Lei et al., 2009), it is likely that stagnant slab from prior 
subduction is responsible for continental crust signatures in the magma.  This 
conclusion is further reinforced by the presence of high-velocity anomalies in the 
mantle transition zone (Lei et al., 2009).  
 Typically, rocks showing 238U excesses indicate a continental subduction 
source because U is more easily mobilized in fluid, representing fluid fluxing in the 
74 
 
mantle.  The dehydration of mantle previously metasomatized by subduction is a 
likely source for the 238U excesses in some Tengchong volcanic field magmas (Wang, 
F. et al., 2006).  Indeed, most samples from Maanshan volcano show 238U excesses 
(Wang, F. et al., 2006; Zou et al., 2010).  
 The Dayingshan sample in this study measured slight 230Th enrichment 
relative to 238U, with 230Th excesses of ~4.8%.  230Th excesses in Dayingshan rocks 
have also been reported by Wang, F. et al. (2006).  The presence of both 238U excess 
and slight 230Th excess lavas is commonly observed in continental arc volcanoes, 
even within a single volcano (e.g. Garrison et al., 2006).  During decompressional 
melting, several factors may influence the ratio of 230Th to 238U, however only the 
bulk partition coefficients, and thus the source mineralogy, determine whether 
230Th/238U is greater than or less than 1 (Zou et al., 2003).  The range in U-Th 
disequilibrium at Maanshan and Dayingshan may be due to melting of a mantle with 
heterogeneous source mineralogy as a result of variable fluid addition and sediment 
contribution, which are to be expected in a continental arc setting.  
75 
 
CONCLUSIONS 
 Volcanism in the Tengchong volcanic field has been active since the late 
Tertiary, and has been punctuated by four major eruptive stages representing 
slightly different magmatic compositions.  Varying major and trace element 
signatures, as well as structural and tectonic complexities in the formation of the 
region, have created questions regarding the formation and magmatic evolution of 
the volcanic field.  Dayingshan is one of the three most recently active volcanoes in 
the field.  Due to a relative abundance of zircon, rocks from the Tengchong volcanic 
field can be radiometrically dated using 238U-230Th dating methods.  The spatial 
resolution, low background and high sensitivity capabilities of SIMS are required to date 
the zircons due to their relatively small sizes and low Th abundances in the Quaternary 
rocks. 
 The Dayingshan zircons indicate two age populations at 58 ? 13 ka and 87.5 
? 6.5 ka.  The older population most likely represents zircon antecrysts that were 
formed in an earlier phase of magmatism, but remained in the magma chamber and 
remobilized in a second magmatic phase.  The younger population represents 
phenocrystic growth in the most recent magma body.  Using this age population, a 
magma chamber storage time of 48 ka is deduced by subtracting the most recent 
eruption age (~10 ka) from the zircon age.   
 
76 
 
 Dayingshan whole-rock major and trace element analysis yielded high Zr 
concentrations and an overall calc-alkaline trend.  Enrichment in LREE?s and 
incompatible elements, and depletion in elements with high field strengths were 
measured, and are typical in subduction-related melts.  The whole-rock chemistry 
points to a metaluminous signature, and measurements of zircon saturation indicate 
that the melt was saturated with respect to Zr.  These factors indicate that there is 
no incorporation of zircon xenocrysts from the country rock.  This conclusion is 
further reinforced by the fact that no zircon has yet been found in the Dayingshan 
lavas to date as old as the country rock.  Trace element and isotopic data from this 
and other studies have found enriched mantle characteristics, indicating a crustal 
component in the melt.  This has lead to the conclusion that the magma likely 
originated from fluid fluxing off of a stagnant slab from a prior subduction event.       
 Major and trace element analysis and calculated ages for zircons from 
Dayingshan and Maanshan (Zou et al., 2010) have yielded similar results.  The slight 
range in whole-rock U-Th disequilibrium at Maanshan and Dayingshan may be due 
to melting of a mantle with heterogenous source mineralogy as result of variable 
fluid addition and sediment contribution, which is to be expected in a continental 
arc setting.
77 
 
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