南天山北缘白土塘蛇绿混杂岩构造环境

Tectonic Setting of the Baitutang Ophiolite at the Northern Margin of South Tianshan Belt

新疆南天山北缘白土塘出露一部分蛇绿混杂岩,为了解其中超基性-基性岩的形成环境,笔者主要利用地球化学的研究方法对该区的9个样品进行了测试。通过地球化学研究分析,认为本区的蛇纹岩以低SiO2、TiO2、CaO、K2O、Na2O,高MgO、Al2O3为特征,富集相容元素Cr、Co、Ni,贫不相容元素,同时大离子亲石元素含量较低,整体特征类似于大洋二辉橄榄岩,具有地幔残留物的特征。对玄武岩的地球化学研究表明,其以富TiO2、MgO,贫Al2O3、K2O,且Na2O>K2O为特征;与MORB相比较,明显亏损Nb、Ta;与原始地幔相比较,具有类似于N-MORB的亏损地慢特征;主、微量元素的地球化学特征显示岩石应形成于类似洋中脊的构造环境,岩浆源于亏损地幔区。

There exposed part of the Ophiolitic Melange in Baitutang, the norht of the South Tianshan in Xinjiang. To understand the ultrabasic rocks forming environment, this paper focuses on the 9 samples of this area are tested by the study of geochemical method. Research and analysis of the geochemical results that the serpentinite in the area with low SiO2, TiO2, CaO, K2 O, Na2O, MgO, Al2O3 for the characteristics, with high concentration of compatible elements Cr, Co, and Ni, depleted in incompatible elements, and large ion lithophile element content is low, the overall features similar to the Ocean lherzolite, features representing the man- tleresidue. The basalts possess high TiO2 and MgO contents, not only low Al2O3 and K2O, but also Na1O〉K2O. Compared with MORB, the elements of Nb, Ta apparent are loss. Compared with the primitive mantle, with slow features sdmilar to the N-MORBrs losses, The geochemical characteristics of the main elements and trace elements show that rock should be formed in the tectonic environment similar to mid-ocean ridge, and the magma derived from depleted mantle zone.