Geochemical Studies of Primitive Melt Inclusions from Mt. Shasta

清水EAR-0106578本项目是对卡斯卡迪亚俯冲带的熔融和熔体迁移过程进行的研究。沙斯塔，加利福尼亚州北部。卡斯卡迪亚系统代表了最热的俯冲系统之一，在这里可以定量地测试板岩派生的熔体成分的贡献。在俯冲带系统中，从未对原始熔融包裹体进行过详细的地球化学研究。拟议工作的重点是：(1)关注原始熔体，以便对熔体生成过程有新的认识；(2)关注熔体包裹体，以便捕获熔体成分的代表性光谱，并确定喷发前挥发成分；以及(3)表征年轻热俯冲系统的端元案例。这项拟议工作的主要目标是确定所有主要喷发阶段所涉及的熔体的地球化学特征，这些熔体形成了山的大厦。沙斯塔。拟议的工作将分以下步骤进行：(1)记录每个样品中熔体包裹体之间的地球化学变化；(2)澄清熔体包裹体与寄主岩石之间的关系；(3)评估每个喷发阶段不同喷发单元之间的地球化学变化；(4)评估主要喷发阶段的时间地球化学趋势。橄榄石中的熔融包裹体将使用索博列夫式加热阶段进行均质，并将用电子探针分析主要元素。离子探针分析将按从B和铅同位素组成开始的顺序进行，然后是轻元素(Li、Be、B、H2O)、稀土(La、Ce、Nd、Sm、Dy、Er、Yb)、高场强元素(Ti、Zr、Nb)、碱土(Ba、Sr)和Y的微量元素分析。

ShimizuEAR-0106578This project is an investigation of melting and melt migration processes operating for the Cascadia subduction zone using the geochemical analyses of primitive melt inclusion hosted in high-Mg olivine phenocrysts from Mt. Shasta, northern California. The Cascadia system represents one of the hottest subduction systems where contributions of slab-derived melt components could be tested quantitatively. A detailed geochemical study of primitive melt inclusions as proposed here has never been carried out for a subduction zone system. The emphasis of the proposed work is: (1) to focus on primitive melts so that new insights into processes of melt generation could be gained; (2) to focus on melt inclusions so that a representative spectrum of melt composition can be captured, and pre-eruptive volatile contents can be determined; and (3) to characterize an endmember case for hot young subduction system. The primary objective of the proposed work is to establish a geochemical characterizationof melts involved in all major eruptive stages that created edifices of Mt. Shasta. The proposed work will be carried out in the following steps: (1) documentation of geochemical variabilities among melt inclusions in each sample; (2) clarification of the relationships between melt inclusions and host rock; (3) evaluation of geochemical variabilities among separate eruptive units within each eruptive stage; (4) assessment of temporal geochemical trends for the major eruptive stages. Melt inclusions in olivines will be homogenized using a Sobolev-type heating stage, and will be analyzed for major elements with an electron probe. Ion probe analyses will be made in a sequence beginning with B and Pb isotope compositions, followed by trace element analysis for light elements (Li, Be, B, H2O ), REE (La, Ce, Nd, Sm, Dy, Er, Yb), HFSE (Ti, Zr, Nb), alkaline earths (Ba, Sr) and Y.