Tracing subducted black shales in the Lesser Antilles arc using molybdenum isotope ratios
Tracing subducted black shales in the Lesser Antilles arc using molybdenum isotope ratios
复制标题
DOI：
10.1130/g38344.1
复制
发表时间：
2016-12
期刊：
影响因子：
5.8
通讯作者：
H. Freymuth;T. Elliott;M. V. Soest;S. Skora
中科院分区：
文献类型：
--
作者：
H. Freymuth;T. Elliott;M. V. Soest;S. Skora
小安的列斯弧熔岩具有微量元素和放射性成因同位素特征，表明其大陆源贡献。这一大陆特征是否代表了与大西洋板块一起俯冲并加入地幔楔中的岩浆源的陆源沉积物，或者是岩浆上升过程中被同化的部分弧下地壳，一直存在激烈的争论。本文介绍了小安的列斯弧熔岩和小安的列斯海沟外沉积物的Mo同位素数据。俯冲沉积堆中黑色页岩层序Mo含量高，具有异常高的98Mo/95Mo。尽管它们在沉积物中所占的质量分数很低（在深海钻探项目Site 144中<10%），但在小安的列斯海沟俯冲的大块沉积物中，它们的Mo含量和同位素组成占主导地位。结果表明，小安的列斯岛弧南段的熔岩也具有较高的98Mo/95Mo比值，暗示其地幔源中有来自俯冲黑色页岩的Mo。这在俯冲物质的组成和弧岩浆产出之间建立了新的联系。
Lesser Antilles arc lavas have trace element and radiogenic isotope characteristics indicative of a continent-derived contribution. It is debated vigorously whether this continental signature represents terrigenous sediment that has been subducted with the Atlantic plate and added to the magma sources in the mantle wedge, or portions of the subarc crust that are assimilated during magma ascent. Here we present Mo isotope data for Lesser Antilles arc lavas and sediments offboard the Lesser Antilles trench. Sequences of black shales, present in the subducting sediment piles, are highly enriched in Mo and have unusually high 98Mo/95Mo. Despite their low mass fraction in the sediment package (<10% in Deep Sea Drilling Project Site 144), they dominate the Mo content and isotopic composition of the bulk sediment subducting at the Lesser Antilles trench. We show that lavas from the southern part of the Lesser Antilles arc also have high 98Mo/95Mo ratios, implicating the addition of Mo derived from the subducted black shales to their mantle sources. This establishes a new link between the composition of subducted material and the arc lava output.