新疆南天山蛇绿岩的地质地球化学特征及形成环境初探

The Preliminary Studies on Tectonic Environment of Formationand Geological and Geochemical Characters of Ophiolites,South Tianshan Mountains, Xinjiang

南天山蛇绿岩带分布于哈尔克山南坡－霍拉山－带，以色日克牙依拉克剖面的蛇绿岩出露较为完整。地幔橄榄岩主要为方辉橄榄岩，其次为含单斜辉石的方辉橄榄岩和纯橄岩，堆晶辉长岩可能已变质为斜长角门质糜棱岩，枕状熔岩主要为Ｎ－ＭＯＲＢ。枕状熔岩的８７Ｓｒ／８６Ｓｒ初始比值较高（０．７６４～０．７０９９），△２０７Ｐｈ／２０４Ｐｈ（８．７１～２３．５４），△２０８Ｐｈ／２０４Ｐｈ（４１．２３～７８．７５），△Ｎｄ（６．７５～１５．０９），表明南天山蛇绿岩的源区为亏损的软流圈地幔（ＤＭＭ）与第２类富集地幔（ＥＭＩＩ）相混合的异常地幔区。南天山蛇绿岩形成于晚古生代早期塔里木板块和南天山微板块之间的有限洋盆环境。

The assemblages of ophiolitic units occur relatively completely along the Serikeyayilake sectionamong the South Tianshan ophiolite belt, which distributes from southern slope of Harakeshan Mountains toHuolashan Mountains. The mantle peridotites are mainly harzburgites, with clinopyroxene-bearing harzburgitesand dunnes. The porphyroclastic textures exist in the mantle peridotites. The high-temperature gliding system(010) [100] also exists in the potphyroclastic olivines. The cumulate gabbros may have been metamorphosed toplagioclase -amphibolite-mylonitic schists. The pillow lavas are mainly N-MORB, minorly E-MORB. Thesilicalites deposited above the lavas at Kula Lake contain radiolaria fossils (D3-C1). The high initial ratios of87Sr/86Sr(0. 706399￣0. 709825) and △207Pb/204Pb(8. 71 ￣ 23. 54), △208Pb/204Pb(41. 23￣78. 75), △Nd(6.75￣ 15. 09) indicate that the source area of the South Tianshan ophiolites was an abnormal mantle, which was mixedby the depleted asthenosphere mantle (DMM) and the second enriched mantle (EMll). The South Tianshanophiolites were formed in a small oceanic basin, which existed between the Tarim plate and the South Tianshanmicro-plate in the early time of the late Paleozoic.