Geochemical Studies of Primitive Melt Inclusions from Mt. Shasta

沙斯塔山原始熔体包裹体的地球化学研究

• 批准号: 0106578
• 负责人: Nobumichi Shimizu
• 金额: $ 22.48万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-01 至 2006-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0106578&HistoricalAwards=false
• 关键词: Geochemical; Studies; Primitive; Melt; Inclusions

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.

Shimizu-0106578本项目是利用对来自Mt.沙斯塔，北方加州。卡斯卡迪亚系统代表了最热的俯冲系统之一，板片衍生的熔体组分的贡献可以定量测试。本文所提出的原始熔融包裹体的地球化学研究，在俯冲带系统中尚未见报道。研究的重点是：（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，以便获得具有代表性的熔体成分谱，并确定喷发前的挥发分含量;（3）表征热年轻俯冲系统的端元情况。建议的工作的主要目标是建立一个地球化学characterizationof熔体参与所有主要的喷发阶段，创造了大厦的山。沙斯塔建议的工作将按以下步骤进行：（1）记录每个样品中熔融包裹体的地球化学变化;（2）澄清熔融包裹体与寄主岩石之间的关系;（3）评价每个喷发阶段内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地球化学时间趋势。橄榄石中的熔体包裹体将使用Sobolev型加热阶段进行均质化，并将用电子探针分析主要元素。离子探针分析将按以下顺序进行：从B和Pb同位素组成开始，然后进行轻元素（Li、Be、B、H2O）、REE（La、Ce、Nd、Sm、Dy、Er、Y B b）、HFSE（Ti、Zr、Nb）、碱土金属（Ba、Sr）和Y的微量元素分析。