当前位置: X-MOL 学术Geochim. Cosmochim. Acta › 论文详情
Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)
Potassium isotopic evidence for sedimentary input to the mantle source of Lesser Antilles lavas
Geochimica et Cosmochimica Acta ( IF 5 ) Pub Date : 2020-12-22 , DOI: 10.1016/j.gca.2020.12.013
Yan Hu , Fang-Zhen Teng , Catherine Chauvel

Arc magmas derived from mantle melting often have trace element and isotopic signatures that indicate crustal contributions. The origin and extent of crustal contributions are critical constraints for quantifying crust-mantle recycling at subduction zones; however, it is difficult to distinguish between inputs from the downgoing oceanic slabs and that of the over-riding arc crust. Here we present a novel study using stable potassium (K) isotopes to fingerprint the long-debated crustal signatures in lavas from Martinique Island, Lesser Antilles arc. We find δ41K of Martinique lavas varies from −0.66 to 0.01‰ and correlates with chemical parameters and radiogenic isotope ratios. These correlations cannot be produced by assimilation of arc crust during magma ascent. Rather, they reflect mantle sources that have been modified by the input of subducted sediments. Most lavas display a strong negative correlation between δ41K and radiogenic isotopic compositions, from typical mantle values of −0.37‰ to much lower values of −0.66‰, suggesting the addition of <1% to 5% subducted sediments to their mantle sources. Notable divergence in this correlation occurs for three samples with variably high δ41K (−0.28 to 0.01‰), which is likely caused by the addition of isotopically heavy K-bearing fluids derived from slab dehydration. Our study indicates that a substantial fraction of large ion lithophile elements, including K in arc magmas and thus nascent crust, is inherited from subducted crust; K isotopes are useful tracers of this cycling process.



中文翻译:

沉积到小安的列斯群岛熔岩地幔源的沉积物的钾同位素证据

来自地幔融化的弧岩浆通常具有痕量元素和同位素特征,表明地壳的贡献。地壳贡献的来源和程度是量化俯冲带壳幔循环利用的关键条件。但是,很难区分正在下降的大洋板块的输入和上覆弧形地壳的输入。在这里,我们提出了一项新的研究,利用稳定的钾(K)同位素对小安地列斯群岛马提尼克岛熔岩中长期辩论的地壳特征进行指纹识别。我们发现δ 41马提尼克岛熔岩的K值在-0.66至0.01‰之间,与化学参数和放射同位素比值相关。这些相关性不能通过岩浆上升过程中的地壳同化来产生。相反,它们反映了被俯冲沉积物输入改变的地幔源。最熔岩显示δ之间有很强的负相关性41 K和放射同位素组合物的-0.66低得多的值‰,这表明添加的<1%至5%的俯冲沉积物其地幔源,从-0.37‰典型地幔值。在此相关性显着的发散发生对三个样本具有可变高δ 41K(-0.28至0.01‰),这很可能是由于添加了源自平板脱水的同位素重的含K流体而引起的。我们的研究表明,很大一部分的离子亲石元素,包括弧状岩浆中的K以及新生的地壳,都是从俯冲的地壳继承而来的。钾同位素是该循环过程的有用示踪剂。

更新日期:2021-01-11
down
wechat
bug