Ion Microprobe Dating of Zircons from Heikongshan Volcano (Tengchong Volcanic Field, Southeast Tibetan Plateau): Time Scales and Nature of Magma Storage

Abstract

Although Cenezoic post-collisional volcanism is widespread on the Tibetan Plateau, young volcanoes suitable for studying the timescales of magma chamber processes are rather rare. Three young potassic volcanoes (Maanshan, Dayingshan, and Heikongshan) from the Tengchong area, southeast Tibetan Plateau, have been reported with eruption ages of less than 10 ka. The potassic lavas contain information about melt generation and magma chamber processes underneath the Tibetan Plateau. There is now a general consensus that pre-eruption zircon growth can be used to constrain the time scales of magma chamber processes. In the present study, we utilize a secondary ion mass spectrometry to measure U-Th zircon ages from the Heikongshan volcano to estimate magma residence times. The U-Th ages of zircon yielded ages of 67.3 ± 14 ka and 99.9 ± 4.6 ka, which represent two stages of zircon crystallization. Using an eruption age of < 10 ka, the zircon storage time in the magma chamber is at least 57.3 ka. Combining geochemical analysis with previous geologic study in the Tengchong area, the Heikongshan magma is probably derived from partial melting of an enriched mantle metasomatized by fluids from previous north-dipping subduction. This study will contribute to a broader understanding of the behavior and hazard of the Tengchong volcanic system.