Ion Probe Dating of Zircons from Wuluke Volcano, NW Tibet, China: Constraints on Magma Evolution

Abstract

The Ashikule volcanic cluster (AVC) is located in the Ashikule basin, on top of the Kunlun Mountains in the NW Tibetan Plateau. There is very little research on the AVC, so further research is necessary in order to gain a better understanding of the volcanology and magmatic process associated with the northern Tibet plateau. The Wuluke volcano is located in the central east area of the AVC and it is currently covered in late Pleistocene to Holocene lava flows. These young volcanic rocks derive from a potassic melt and contain an abundance of zircon grains. Zircon has played a key role in geochronology and crustal evolution studies. Zircon xenocrysts have long been considered burdensome because they can hinder magmatic age estimation. However, a growing number of studies have shown that xenocrystic zircons can provide valuable information on magma evolution and crustal contamination. This research utilizes U-Pb dating methods and secondary ion mass spectrometry (SIMS) to date zircons from the Wuluke volcano, which can be used to provide constraints on magma evolution and contamination processes. Measured zircons yielded multiple zircon age populations ranging from the most recent eruption to the Proterozoic. The Proterozoic ages correlate well with known country rock ages indicating that the sample contains both phenocryst and xenocryst zircons providing evidence that lavas from the Wuluke volcano have experienced crustal contamination through the assimilation of zircon-bearing country rocks. Electron microprobe analyses of orthopyroxene and plagioclase phenocrysts indicate that the early formed phenocrysts remained in equilibrium with the melt and were not affected by crustal contamination.