Evaluating the Processes and Timescales of Rhyolitic Differentiation

点击翻译按钮获取中文摘要

Intellectual merit: U-series isotopes have revolutionized our ability to evaluate magmatic timescales and will be used in conjunction with Rb/Sr systematics to constrain the time in which large volumes of intraplate rhyolite are generated. The timing and processes involved in the generation of silicic magmas are relevant to modeling activity at potentially explosive volcanoes, with significant climate and volcanic hazard implications. Baitoushan volcano (NE China/North Korea) is ideally suited for such studies because it has produced multiple young high silica rhyolites including a large volume (~100 km3) pyroclastic eruption as recently as ~1000 AD. All eruptive units are sufficiently young that both short-lived 238U-230Th-226Ra and 235U-231Pa isotopic systems as well as long-lived radiogenic isotopes can be used in combination to assess magmatic timescales. Moreover, sampling is sufficient to carry out the proposed work, thus saving on the time and cost of the proposed research. Timing of magmatic fractionation events involved in the generation of associated mafic and silicic magmas in this volcano will be evaluated through analysis of accessory phenocryst minerals. Single crystal Pb and Sr isotope analyses will also be used as tracers to quantify the effects of open-system processes such as crustal contamination, magma recharge, and post-eruption alteration. In combination these data will allow detailed assessment of such processes on the overall evolution of the volcano as well as their effects on the fidelity of the various isotopic dating methods.Broader Impacts include (1) involvement of an undergraduate into cutting-edge research in the geological sciences, (2) international collaborations, and (3) relevance to volcanic risk assessment. Regarding the latter point, a "seismic crisis" at Baitoushan within the last decade raised concerns that the volcano could erupt again in the near future. Better understaning of the timescale of magma evolution could be useful in predicting future activity. Finally, Baitoushan's location on the border between China and North Korea (DPRK) has potential political significance, and contributions to understanding volcanic behavior could promote international 'good will'.