阿拉善北部恩格尔乌苏蛇绿混杂岩的形成机制

The Original Mechanism of the Engger Us Ophiolitic Melange, North Alaxa

恩格尔乌苏蛇绿混杂岩是华北板块与塔里木板块结合的标志，研究结果表明蛇绿岩可分为上俯冲带型（ＳＳＺ）和洋脊型（ＭＯＲＢ）两类，混杂岩中部分砂岩源自塔里木被动大陆边缘，部分源自与ＳＳＺ相关的构造环境和南侧的沙拉扎山火山弧。蛇绿岩形成侵位经历了以下三个阶段：在古洋壳俯冲作用之前，“弧”前拉张作用形成了ＭＯＲＢ型蛇绿岩；古洋壳向南俯冲的早期阶段形成了ＳＳＺ型蛇绿岩和在洋壳俯冲闭合期间，蛇绿岩发生拆离并向北仰冲侵位。蛇绿混杂岩破碎混合作用记录了一种递进变形的应变历史。

The Engger Us ophiolitic melange is considered to be an indicator of the suture between North China and Tarim Plates.The results show that the ophiolites may be divided into two types:supersubduction zone(SSZ) and MORB ophiolites. A part of studied sandstone in the melange is derived from the Tarim passive continental margin, and most of them from the tectonic setting relative to the SSZ ophiolite and the continent-based volcanic arc of Salazhashan. The formation and emplacement of the ophiolites cover three stages:the forearc-spreading producing MORB ophiolite prior to the oceanic crust subduction;SSZ ophiolite formed during the initial stage of the southward subduction; and the detachment and northward obduction of the ophiolites during the subduction-closing period. The disrupting and mingling of the melange may record a strain history of progressive deformation.