Evaluating the Processes and Timescales of Rhyolitic Differentiation

智力优势：铀系列同位素使我们评估岩浆时间尺度的能力发生了革命性的变化，并将与Rb/Sr系统学结合使用，以限制大量板内流纹岩的生成时间。硅质岩浆产生的时间和过程与模拟潜在火山爆发的活动有关，具有重大的气候和火山灾害影响。白头山火山(东北中国/朝鲜)非常适合进行这类研究，因为它产生了多个年轻的高硅流纹岩，包括最近公元1000年的大体积(~100km~3)火山碎屑喷发。所有喷发单元都足够年轻，因此短寿命的~(238)U-~(230)Th-~(226)Ra和~(235)U-~(231)Pa同位素系统以及长寿命的放射性同位素可以结合使用来评估岩浆的时间尺度。此外，抽样就足以进行拟议的工作，从而节省了拟议研究的时间和成本。将通过对副斑晶矿物的分析来评估与该火山伴生的镁铁质和硅质岩浆生成有关的岩浆分馏事件的时间。单晶铅和锶同位素分析也将被用作示踪剂，以量化地壳污染、岩浆补给和喷发后蚀变等开放系统过程的影响。关于后一点，白头山在过去十年中发生的一次“地震危机”引发了人们对该火山可能在不久的将来再次喷发的担忧。更好地了解岩浆演化的时间尺度可能有助于预测未来的活动。最后，白头山位于中国和朝鲜(朝鲜)交界处，具有潜在的政治意义，有助于理解火山活动可能会促进国际上的“善意”。

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'.