新疆哈尔克山蛇绿岩的形成环境

THE FORMATION ENVIRONMENT OF OPHIOLITES IN HAERK MOUNTAINS,XINJANG

哈尔克山蛇绿岩由地幔橄榄岩、辉长辉绿岩和基性熔岩组成。基性熔岩的常量元素、微量元素特征显示其属于ＭＯＲＢ，并具向ＩＡＴ过渡的特点，基性熔岩的稀土元素分布型式类似于Ｎ－ＭＯＲＢ，显示ＬＲＥＥ略亏损、ＨＲＥＥ近平坦。基性熔岩的高８７Ｓｒ／８６Ｓｒ初始比（０．７０１７～０．７０８２）、高δ１８Ｏ（１１．７‰～１３．４‰）、低Ｐｂ／２０４Ｐｂ（１５．９１３～１８．１８８）、相对于２０６Ｐｂ／２０４Ｐｂ来说较高的２０８Ｐｂ／２０４Ｐｂ（３５．７５２～３７．７６７）及１４３Ｎｄ／１４４初始比（０．５１２５５６～０．５１２５９９）均说明蛇绿岩的源区为亏损软流回地幔和第１类富集地幔物质（ＥＭＩ）和第２类富集地幔物质（ＥＭⅡ）相混合的地幔源区，蛇绿岩形成于塔里木板块和南天山微板块之间的小洋盆中初始不成熟岛弧环境。

The ophiolites in Haerk Mountains are composed of mantle peridotites ,gabbro-diabases and basic lavas.The features of major and trace elements of basic lavas reveal that they belong to MORB and have a characteristic of transsition to IAT.The REE disribution pattern of basic lavas is Similar to N-MORB and reveal the LREE deplets slightly ,the HREE is nearly even.The higher (87Sr/86Sr)(0.7077-0.7082), higher 18O(11.7-13.4),lower 206Pb/204Pb(15.913-18.188),higher 208Pb/204Pb (35.752-37.767) relatively to 206Pb/204Pb and the(143Nd/144Nd)0 (0.512556-0.5512599) of basic lavas all indicate that the original region of ophiolites if a mantle original one which is mixed by depleted asthenospheric mantle materials(EMⅠ),the second enriched mantle materials(EM Ⅱ) .The ophiolites originated in original unripe island arc environment in the smalloceanic basin between the Tianshan microplate.