The Origin of Felsic Intrusions Within the Mantle Section of the Samail Ophiolite: Geochemical Evidence for Three Distinct Mixing and Fractionation Trends
The Origin of Felsic Intrusions Within the Mantle Section of the Samail Ophiolite: Geochemical Evidence for Three Distinct Mixing and Fractionation Trends
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DOI：
10.1029/2020jb020760
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发表时间：
2021-03
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通讯作者：
M. Rioux;M. Benoit;I. Amri;G. Ceuleneer;J. Garber;M. Searle;Kayla Leal
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文献类型：
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作者：
M. Rioux;M. Benoit;I. Amri;G. Ceuleneer;J. Garber;M. Searle;Kayla Leal
一套同位素多样性的长英质岩脉、岩床和岩塞(εND(T)=−7.8to+7.8%)侵入阿曼和阿拉伯联合酋长国(阿联酋)萨马尔蛇绿岩的最上地幔和下地壳。这些特征被解释为代表来自大洋岩石圈俯冲岩层的角闪岩和变质沉积熔体。因此，侵入体提供了洋壳和沉积物在深处融化的记录，并暗示了在年轻、热的俯冲环境下从下行板块进行的质量转移。一些研究已经使用地球化学数据来限制岩脉的岩浆来源；在这里，我们使用来自更广泛的地理范围的岩脉套件的综合全岩常量元素、微量元素和Nd同位素数据，在此基础上开展这项工作。新的和现有的数据表明，蛇绿岩阿曼部分地幔橄榄岩中保存的长英质侵入岩是由三种不同的混合和分馏趋势产生的：(1)沉积物熔体、角闪岩熔体和地幔成分之间的三组分混合；(2)角闪岩和沉积物熔体之间的两组分混合，几乎没有地幔贡献；(3)亏损的地幔来源岩浆的分离结晶，可能与蛇绿岩V2火山系列有关。地球化学和假剖面联合模拟表明，角闪岩熔融发生在P≤1.4 Gpa(∼40-45 km)和T≥700-750°C。阿联酋地幔剖面的长英质侵入岩，包括石榴石-红柱石-堇青石-淡绿色花岗岩，具有类似的混合趋势，但在阿曼侵入后结晶∼为0.9-4.0 Ma。
An isotopically diverse suite of felsic dikes, sills, and plugs (εNd(t) = −7.8 to +7.8) intrude the uppermost mantle and lower crust in the Samail ophiolite in Oman and the United Arab Emirates (UAE). These features have been interpreted to represent amphibolite and metasediment melts from an underthrust sheet of oceanic lithosphere. As such, the intrusions provide a record of melting of oceanic crust and sediment at depth, with implications for mass transfer from the down‐going plate in young, hot subduction settings. Several studies have used geochemical data to constrain the magmatic sources of the dikes; here we build on this previous work using integrated whole rock major element, trace element and Nd isotopic data from a more geographically extensive suite of dikes. New and existing data suggest the felsic intrusions preserved within mantle peridotites in the Oman portion of the ophiolite were generated by three distinct mixing and fractionation trends: (1) three‐component mixing between sediment melt, amphibolite melt and a mantle component; (2) two component mixing between amphibolite and sediment melts, with little mantle contribution; and (3) fractional crystallization of depleted, mantle derived magmas, likely related to the ophiolite V2 volcanic series. Combined geochemical and pseudosection modeling suggest that amphibolite melting occurred at P ≤ 1.4 GPa (∼40–45 km) and T ≥ 700–750°C. Felsic intrusions in the mantle section in the UAE, including garnet‐andalusite‐cordierite leucogranites, follow similar mixing trends, but crystallized ∼0.9–4.0 Ma after the Oman intrusions.