ION PROBE DATING OF ZIRCON XENOCRYSTS FROM WULUKE VOLCANO, NORTHWESTERN TIBET, CHINA: CONSTRAINTS ON MAGMA EVOLUTION AND DEEP CRUSTAL EVOLUTION

The Ashikule volcanic cluster (AVC) is located in the Ashikule basin, set on top of the west Kunlun Mountains on the north western margin of the Tibetan Plateau. The Ashikule basin is located in a unique tectonic setting, characterized by ongoing strong tectonic activity. Wuluke, the volcano of interest in this project, is located in the central eastern part of the volcanic cluster. Due to recent nearby eruptions and tectonic activity, it can be assumed that the Wuluke volcano still has eruption potential. Further research within the AVC is needed in order to gain a better understanding of the volcanology and magmatic processes of the north western Tibetan Plateau.

Volcanic rocks in north western Tibetan Plateau contain not only information on mantle sources but also cryptic signals from deep crustal fragments entrained during magma ascent if mineral xenorysts are present. Zircon xenocrcysts with pre-eruption ages captured by the magmas could have originated from mantle derived rocks or assimilation of country rock during the magma’s ascent through the crust. If most xenocrystic zircons can be confirmed as continental crustal zircons (rather than mantle-derived zircons) and if they display multiple age populations, they may be used to probe deep crustal evolution through time. The particular abundance of zircon xenocrysts in the Wuluke volcano rock samples provides an excellent opportunity to study magma origin and evolution by comparing age populations of zircons obtained through Secndary ion mass spectrometry (SIMS). Secondary ion mass spectrometry (SIMS) provides high spatial resolution (<25 μm) for zircon U-Pb dating using spot analysis of polished zircons. SIMS depth profiling of unpolished zircon surfaces offers even higher spatial resolution (~3 μm). The measured age populations, in conjunction with geochemical analysis of the minerals and whole rock, will be used to provide constraints on magma evolution and crustal contamination processes of the Wuluke volcano.