不同构造环境下蛇纹岩化作用的对比-以西南天山和北祁连造山带为例
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1.中国科学院海洋研究所;2.西北大学

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本文接受崂山实验室科技创新项目(LSKJ202204104)资助和中国科学院战略性先导科技专项(B类;项目号XDB42020302)资助


Comparison of serpentinization in different tectonic environments: A case study of the Tianshan and North Qilian orogenic belts in Southwest China
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1.Institute of Oceanology, Chinese Academy of Sciences;2.Northwest University

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    摘要:

    蛇纹石含水量约为13%,是地球重要的含水矿物,广泛分布于洋底、俯冲带、弧前等环境。同时,海水、俯冲带衍生流体中的活动性元素(B、Li、As、Sb、Pb、Cs、U、Sr、Ba)也可随蛇纹石化作用而富集在蛇纹石中。因此,蛇纹石可以作为流体和流体活动性元素的载体参与不同的地质过程。然而,不同的构造环境有不同的温度压力、水岩比值、流体性质、氧化还原条件。不同环境下的蛇纹石化作用,不仅会形成不同种类的蛇纹石(例如利蛇纹石,叶蛇纹石),也有可能会导致蛇纹石的元素富集特征不同,这就需要进一步研究流体活动性元素的地球化学行为和元素富集特征。基于对世界范围内不同环境蛇纹岩数据资料的整理分析,结合西南天山和祁连山两个典型造山带的蛇纹岩样品,我们发现深海蛇纹岩与俯冲带蛇纹岩,B、Ba、Cs表现出不同的富集特征:(1)深海蛇纹岩具有明显更高的B元素含量,可能反映了B在低温下更容易进入到蛇纹岩中;(2)俯冲带以及弧前环境下形成的蛇纹岩由于可能有沉积物的输入,Ba、Cs的含量相对较高。这一结论有助于以后通过蛇纹岩的元素地球化学特征反演其相对的构造环境。

    Abstract:

    Serpentine, with a water content of about 13%, is an important hydrated mineral on the earth and widely distributed in different tectonic environments, e.g., the ocean floor, subduction zones and fore-arcs. Except fluids, fluid-mobile elements (B, Li, As, Sb, Pb, Cs, U, Sr, Ba) can be also enriched in serpentine with serpentinization. Thus, serpentine can be present as the important host for fluids and these elements in different geological processes. However, different tectonic environments have varying temperatures and pressures with potentially different properties of fluids. Serpentinization in different environments cannot only result in the formation of different serpentines (e.g., lizardite, antigorite), but may also lead to different enriched characteristics of serpentine, which require further studies. Based on comparison of compiled literature data for serpentinite produced in different tectonic environments worldwide, together with the serpentinite samples from two typical orogenic belts of Southwest Tianshan and Qilian Mountains, we found that abyssal serpentinite and serpentinite in subduction zones show different enriched characteristics of B, Ba and Cs : (1) abyssal serpentinite has significantly higher B contents, which may reflect the preference of B to serpentinite at lower temperature; (2) Ba and Cs contents of serpentinite formed in subduction zones are relatively higher, which may indicate tbe contribution of subducting sediments. This conclusion is helpful for interpreting the tectonic environment for serpentinite through its compositional characteristics.

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  • 收稿日期:2022-10-25
  • 最后修改日期:2023-01-19
  • 录用日期:2023-01-19
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