Source Versus Crustal Contamination in Subduction Processes

由于地幔源区的混染作用和岩石圈地幔或地壳岩石在上升和侵位过程中同化作用对幔源岩浆的混染作用产生了相似的地球化学特征，因此，理解大陆弧岩浆成因是困难的。 我们一直在研究跨墨西哥火山带（TMVB），以限制这些过程。我们认为我们以前的工作已经表明，187 Os/188 Os是同化的一个很好的替代，低187 Os/188 Os（0.13-0.15）样品的地球化学主要是源污染的结果，而高187 Os/188 Os（0.15-0.45）样品的地球化学是一个更复杂的历史，包括同化的结果。能够破译不同的输入到弧岩浆提供了一个机会，耦合其他元素和同位素系统到这个框架，以帮助解开不同的输入源污染和同化。我们建议进一步研究，大陆弧火山活动沿着跨墨西哥火山带，我们利用的主要和微量元素的组合方法与Os，Pb，Sr和O同位素分析的全岩或橄榄石和磁铁矿矿物分离的先前表征的样品，以及新的样品从关键地点。这些数据将被用来限制源与地壳污染的不同成分和同位素系统的岩浆成因在这一弧的相对重要性。具体而言，我们将研究：1）个别区域内和从西到东横跨整个墨西哥弧的玄武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区（帕尔马索拉）是否与科科斯板块的俯冲有关，或者是与俯冲无关的东部碱性区的一部分。

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.