A Crustal Control on the Fe Isotope Systematics of Volcanic Arcs Revealed in Plutonic Xenoliths From the Lesser Antilles
A Crustal Control on the Fe Isotope Systematics of Volcanic Arcs Revealed in Plutonic Xenoliths From the Lesser Antilles
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DOI：
10.3389/feart.2021.795858
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发表时间：
2022-01
期刊：
影响因子：
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通讯作者：
G. Cooper;E. Inglis
中科院分区：
文献类型：
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作者：
G. Cooper;E. Inglis
俯冲带产生的熔岩代表了源区异质性和一系列地壳过程的整合，如：分异、混合、均质化、同化。因此，当孤立地使用混合的最终产物时，很难解开弧下地幔源与这些地壳过程的相对贡献。相比之下，深成捕虏体提供了岩浆管道系统的更深的根源的补充记录，并提供了弧壳的真正的化学多样性的独特记录。在这里，我们提出的δ 56 Fe记录，以及特点深成捕虏体从两个不同的火山中心在小安的列斯群岛的火山弧马提尼克岛和Statia。本研究的主要目的是测试，如果弧熔岩的铁同位素系统控制的弧下地幔输入或在随后的分化过程中，岩浆的旅程通过火山弧地壳。Fe同位素记录，再加上岩石学，微量元素化学和放射性同位素的深成包体从两个岛屿揭示了一个隐藏的地壳水库的重Fe，以前没有被认为。铁同位素与放射性同位素脱钩，表明地壳和/或沉积物同化作用并不控制弧岩浆的Fe系统学。与岛弧熔岩相反，两个岛屿的堆积物记录了类似于MORB的δ 56 Fe值。在Statia，δ 56 Fe随主量和微量元素分异指标（SiO2、Na 2 O + K2 O、Eu/Eu*、Dy/Yb）的降低而降低，这与矿物组合沿着一条液体下降线分馏一致。在马提尼克岛，δ 56 Fe与大多数分异指标（除Dy/Yb外）没有明显的关系，表明深成捕虏体的δ 56 Fe特征已被后期过程所叠加，如反应熔体的变质作用。总之，这些数据表明，岩浆过程中的弧下地壳覆盖的弧下地幔的任何源的变化和轻铁源是不是一个要求，以产生轻铁同位素组成记录在火山弧熔岩。因此，只要有可能，在同位素研究中应考虑补充的深成记录，以了解地幔源对地壳岩浆过程的相对控制。
Lavas produced at subduction zones represent the integration of both source heterogeneity and an array of crustal processes, such as: differentiation; mixing; homogenisation; assimilation. Therefore, unravelling the relative contribution of the sub-arc mantle source versus these crustal processes is difficult when using the amalgamated end products in isolation. In contrast, plutonic xenoliths provide a complementary record of the deeper roots of the magmatic plumbing system and provide a unique record of the true chemical diversity of arc crust. Here, we present the δ56Fe record from well characterised plutonic xenoliths from two distinct volcanic centres in the Lesser Antilles volcanic arc–the islands of Martinique and Statia. The primary objective of this study is to test if the Fe isotope systematics of arc lavas are controlled by sub-arc mantle inputs or during subsequent differentiation processes during a magma’s journey through volcanic arc crust. The Fe isotopic record, coupled to petrology, trace element chemistry and radiogenic isotopes of plutonic xenoliths from the two islands reveal a hidden crustal reservoir of heavy Fe that previously hasn’t been considered. Iron isotopes are decoupled from radiogenic isotopes, suggesting that crustal and/or sediment assimilation does not control the Fe systematics of arc magmas. In contrast to arc lavas, the cumulates from both islands record MORB-like δ56Fe values. In Statia, δ56Fe decreases with major and trace element indicators of differentiation (SiO2, Na2O + K2O, Eu/Eu*, Dy/Yb), consistent with fractionating mineral assemblages along a line of liquid descent. In Martinique, δ56Fe shows no clear relationship with most indicators of differentiation (apart from Dy/Yb), suggesting that the δ56Fe signature of the plutonic xenoliths has been overprinted by later stage processes, such as percolating reactive melts. Together, these data suggest that magmatic processes within the sub-arc crust overprint any source variation of the sub-arc mantle and that a light Fe source is not a requirement to produce the light Fe isotopic compositions recorded in volcanic arc lavas. Therefore, whenever possible, the complimentary plutonic record should be considered in isotopic studies to understand the relative control of the mantle source versus magmatic processes in the crust.