摘要
蛇纹石含水量约为13％,是地球上重要的含水矿物,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,a hydrated mineral with a water content of about 13％,holds great significance on Earth.It is widely distributed across various tectonic environments,such as the ocean floor,subduction zones,and fore-arcs.In addition to fluids,serpentine can also be enriched with fluid-mobile elements(B,Li,As,Sb,Pb,Cs,U,Sr and Ba)through the process of serpentinization.This makes serpentine a crucial host for fluids and these elements in different geological processes.However,different tectonic environments have varying temperatures and pressures,which can result in different properties of fluids.Serpentinization in different environments not only leads to the formation of different types of serpentines(e.g.,lizardite,antigorite),but also results in varying enriched characteristics of serpentine.Thus,further studies are required to understand these differences.By comparing literature data on serpentinite produced in different tectonic environments worldwide,as well as analyzing serpentinite samples from the Southwest Tianshan and Qilian Mountains orogenic belts,we have observed distinct enriched characteristics of B,Ba,and Cs in abyssal serpentinite and serpentinite found in subduction zones:①abyssal serpentinite has significantly higher B contents,suggesting a preference for B in serpentinite formation at lower temperatures;② serpentinite formed in subduction zones displays relatively higher Ba,Cs,and Pb contents,indicating a potential contribution from subducting sediments.This conclusion is valuable in interpreting the tectonic environment associated with serpentinite based on its compositional characteristics.
基金项目
崂山实验室科技创新项目(LSKJ202204104)
中国科学院战略性先导科技专项(B类)(XDB42020302)
泰山学者工程()
万方数据