Source Versus Crustal Contamination in Subduction Processes

俯冲过程中的源头与地壳污染

• 批准号: 0125773
• 负责人: John Chesley
• 金额: $ 5.34万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-01-01 至 2002-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0125773&HistoricalAwards=false
• 关键词: Source; Versus; Crustal; Contamination; Subduction

ChesleyEAR-0125773Understanding magma genesis in continental arcs is difficult because contamination in the mantle source area and contamination of mantle-derived magmas by assimilation of lithospheric mantle or crustal rocks during ascent and emplacement produce similar geochemical characteristics. We have been studying the trans-Mexican volcanic belt (TMVB) in order to constrain these processes. We feel our previous work has shown that 187Os/188Os is an excellent proxy for assimilation, the geochemistry of samples with low 187Os/188Os (0.13-0.15) is primarily the result of source contamination, whereas geochemistry of samples with high 187Os/188Os (0.15-0.45) is the result of a more complex history that includes assimilation. The ability to decipher different inputs into arc magmas offers an opportunity to couple other elemental and isotopic systems into this framework to help unravel different inputs from source contamination and assimilation. We propose further study, of continental arc volcanism along the Trans-Mexican volcanic belt, whereby we utilize a combined approach of major and trace elements with Os, Pb, Sr and O isotopic analysis on whole rock or olivine and magnetite mineral separates of previously characterized samples, together with new samples from key localities. These data will be used to constrain the relative importance of source vs. crustal contamination for different components and isotopic systems in magma genesis across this arc. Specifically, we will examine: 1) The relative roles of mantle source contamination versus crustal contamination in basaltic magmas within individual fields and across the entire Mexican arc from west to east. 2) Determine whether volcanic fields (Palma Sola) in eastern Mexico are related to subduction of the Cocos plate or are part of the eastern alkalic province, which is unrelated to subduction.

ChesleyEAR-0125773了解大陆弧中的岩浆成因很困难，因为地幔源区的污染和上升和侵位过程中岩石圈地幔或地壳岩石同化对地幔源岩浆的污染产生了相似的地球化学特征。 我们一直在研究跨墨西哥火山带（TMVB），以限制这些过程。我们认为我们之前的工作表明 187Os/188Os 是同化的一个很好的代表，具有低 187Os/188Os (0.13-0.15) 的样品的地球化学主要是源污染的结果，而具有高 187Os/188Os (0.15-0.45) 的样品的地球化学是包括同化在内的更复杂历史的结果。破译弧岩浆不同输入的能力提供了将其他元素和同位素系统耦合到该框架中的机会，以帮助阐明来自源污染和同化的不同输入。我们建议进一步研究跨墨西哥火山带沿线的大陆弧火山活动，利用主量元素和微量元素的组合方法，对先前表征样品的整个岩石或橄榄石和磁铁矿矿物分离物进行锇、铅、锶和氧同位素分析，以及来自关键地点的新样品。这些数据将用于限制该弧上岩浆成因中不同成分和同位素系统的来源与地壳污染的相对重要性。具体来说，我们将研究： 1）在各个区域内以及从西到东整个墨西哥弧上，玄武岩岩浆中地幔源污染与地壳污染的相对作用。 2）确定墨西哥东部的火山田（帕尔马索拉）是否与科科斯板块俯冲有关，或者是与俯冲无关的东部碱性省的一部分。