Geochemical Studies of Primitive Melt Inclusions from Mt. Shasta

本项目通过对加利福尼亚北部沙斯塔山高镁橄榄石斑晶中原始熔体包裹体的地球化学分析，研究了Cascadia俯冲带的熔融和熔融迁移过程。卡斯卡迪亚系统是最热的俯冲系统之一，可以定量测试板块衍生熔体成分的贡献。本文提出的原始熔体包裹体的详细地球化学研究从未在俯冲带系统中进行过。提出的工作重点是：(1)关注原始熔体，从而获得对熔体生成过程的新见解；(2)关注熔体包裹体，捕捉熔体组成的代表性光谱，确定喷发前挥发性含量；(3)描述了热年轻俯冲系统的端元情况。拟议工作的主要目标是建立一个地球化学特征的熔体涉及所有主要的喷发阶段，创造了沙斯塔山的大厦。建议的工作将在以下步骤中进行：(1)记录每个样品中熔体包裹体的地球化学变异；(2)明确了熔体包裹体与寄主岩石的关系；(3)评价各喷发阶段各喷发单元的地球化学变异；(4)主要喷发期地球化学变化趋势评价。橄榄石中的熔体包裹体将使用sobolev型加热阶段进行均匀化，并用电子探针对主要元素进行分析。离子探针分析将从B和Pb同位素组成开始，然后是微量元素分析，包括轻元素（Li, be， B, H2O）， REE (La, Ce, Nd, Sm, Dy, Er, Yb), HFSE (Ti, Zr, Nb)，碱土（Ba, Sr）和Y。

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.