Trace element behavior during serpentinization/de-serpentinization of an eclogitized oceanic lithosphere: A LA-ICPMS study of the Lanzo ultramafic massif (Western Alps)
Trace element behavior during serpentinization/de-serpentinization of an eclogitized oceanic lithosphere: A LA-ICPMS study of the Lanzo ultramafic massif (Western Alps)
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DOI：
10.1016/j.chemgeo.2013.08.025
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发表时间：
2013-10-24
期刊：
影响因子：
3.9
通讯作者：
Lafay, Romain
中科院分区：
文献类型：
--
作者：
Debret, Baptiste;Andreani, Muriel;Lafay, Romain
蛇纹岩是海洋岩石圈的主要组成部分之一，在俯冲带中，蛇纹岩稳定存在于100 ~ 150 km深的板块和地幔楔中。在大洋地幔水化蚀变过程中，它们捕获了微量元素和流体流动元素（FME: B、Li、As、Sb、Rb、Ba、Cs、Sr、U和Pb），参与了在俯冲背景下发生在脱水板块和地幔楔之间的元素转移。Lanzo地块是一个榴辉化的海洋岩石圈，保存了其海洋结构，记录了从海洋蜥蜴长岩到俯冲背景下的顺行反长岩，直至脱水和次生橄榄石结晶，最后在地块挖掘过程中逆行反长岩的不同阶段的蛇纹石化/去蛇纹石化。它是研究蛇纹岩化/去蛇纹岩化过程中微量元素行为以及海洋岩石圈和地幔楔之间不同包裹体之间相关化学转移的合适场所。对蛇纹岩及其伴生矿物的地球化学分析表明，兰佐地块的蛇纹岩化/去蛇纹岩化发生在一个相对封闭的体系中，没有明显的微量元素在海洋岩石圈不同部分之间的转移。在岩石圈的较深处，从略蛇纹岩化的地幔橄榄岩（SSP， 90%蛇纹岩化）。在该地区，高寒变形增强了微量元素的流动性，并使其在地块尺度上重新分布和反长花岗岩组成均质化。在局部，在SSP和MS中，类似1-2 m的变质脉的结晶对应于通道化的流体流动，这使得流体（从而微量元素）能够转移到更远的距离。反长岩和橄榄石的连续结晶过程伴随着一些FME （B、Li、As、Sb、Ba、Rb）和Eu含量的减少，证明这些元素是在俯冲过程中从板块转移到地幔楔的。(C) 2013 Elsevier b.v.版权所有
Serpentinites are one of the major components of the oceanic lithosphere and are stable in the slab and the mantle wedge up to 100-150 km depth in subduction zones. During oceanic mantle hydration and alteration, they trap trace and fluid mobile (FME: B, Li, As, Sb, Rb, Ba, Cs, Sr, U and Pb) elements that participate to elemental transfer occurring between the dehydrating slab and the mantle wedge in subduction context. The Lanzo massif is an eclogitized oceanic lithosphere that preserved its oceanic structure and recorded different steps of serpentinization/de-serpentinization from oceanic lizardite to prograde antigorite in subduction context, up to its dehydration and secondary olivine crystallization, and finally retrograde antigorite during massif exhumation. It constitutes a suitable place to study trace element behavior during serpentinization/de-serpentinization processes and associated chemical transfers between the different envelopes of the oceanic lithosphere and the mantle wedge.Geochemical analyses of serpentine and associated minerals show that the serpentinization/de-serpentinization of the Lanzo massif took place in a relatively closed system without significant trace element transfer between the different parts of the oceanic lithosphere. In the deeper part of the lithosphere, from the slightly serpentinized mantle peridotites (SSP, 90% serpentinization). In that zone, the alpine deformation enhances the mobility of trace elements and permits their redistribution and the homogenization of antigorite composition at massif scale. Locally, in the SSP and MS, the crystallization of metamorphic veins of similar to 1-2 m corresponds to channelized fluid flows that allowed fluid transfers - and thereby trace elements - to longer distance. The successive crystallizations of antigorite and then olivine are accompanied by a diminution of some FME (B, Li, As, Sb, Ba, Rb) and Eu contents attesting that these elements are removed from slab to mantle wedge during subduction. (C) 2013 Elsevier B. V. All rights reserved.