Source Versus Crustal Contamination in Subduction Processes

由于地幔源区的混染和岩石圈上升侵位过程中岩石圈地幔或地壳岩石同化造成的地幔岩浆混染，很难理解大陆弧岩浆的成因。我们一直在研究横跨墨西哥的火山带(TMVB)，以限制这些过程。我们认为，我们以前的工作表明，187Os/188Os是一个很好的同化指标，低187Os/188Os(0.13-0.15)的样品的地球化学主要是源污染的结果，而高187Os/188Os(0.15-0.45)的样品的地球化学是包括同化作用在内的更复杂历史的结果。破译弧状岩浆的不同输入的能力提供了一个机会，将其他元素和同位素系统耦合到这一框架中，以帮助解开来源污染和同化的不同输入。我们建议对横贯墨西哥火山带的陆弧火山作用进行进一步的研究，利用主量元素和微量元素相结合的方法，对以前表征的样品的全岩或橄榄石和磁铁矿矿物分离进行Os、Pb、Sr和O同位素分析，以及关键地点的新样品。这些数据将被用来限制来源与地壳污染对不同成分和同位素系统在这一弧形岩浆成因中的相对重要性。具体地说，我们将研究：1)从西到东，在各个油田内和整个墨西哥弧内的玄武岩岩浆中，地幔来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(Palma Sola)是与科科斯板块的俯冲有关，还是与俯冲无关的东部碱性省的一部分。

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.