新疆东昆仑达拉库岸镁铁-超镁铁岩的矿物化学及其属性

Mineral chemistry and properties of the Dalaku'an mafic-ultramafic complex,East Kunlun Mountains, Xinjiang

达拉库岸镁铁-超镁铁岩位于东昆仑造山带南带之喀拉米兰晚古生代沟弧系,由二辉橄榄岩、单辉橄榄岩、橄榄辉石岩、单辉岩、含长辉石岩和辉长岩组成。单辉橄榄岩和橄榄辉石岩中橄榄石均为贵橄榄石(Fo=84.55~89.08),其MnO含量为0.13%~0.29%,NiO含量为0.09%~0.28%;单斜辉石为透辉石和普通辉石,其MgO含量为15.12%~16.98%,Fe O含量为3.84%~5.34%,CaO含量为21.10%~22.95%;与蛇绿岩套中的同类岩石的橄榄石和单斜辉石成分存在较大差异,与夏日哈木和金川镁铁-超镁铁岩中同类岩石的矿物成分类似,表明达拉库岸岩体不是蛇绿岩套的组成部分,而是陆壳中的侵入体。单斜辉石成分表明其母岩浆为拉斑玄武质岩浆,可能形成于与俯冲有关的大陆边缘裂谷环境。达拉库岸岩体具有形成岩浆型铜镍硫化物矿床的条件。

The Dalaku＇an mafic-ultramafic complex is located in the Late Paleozoic Karamilan arc zone, which is the southern active zone of the East Kunlun, and consists of lherzolite, wehrlite, olivine websterite, clinopyroxenite, plagioclase-bearing pyroxenite and grabbro. The olivine in the wehrlite and olivine websterite belongs to chrysolite with the Fo value ranging from 84. 55 to 89. 08, and the content of Mn O and Ni O ranging from 0. 13% to0. 29% and 0. 09% to 0. 28%, respectively. The clinopyroxene belongs to diopside and augite with the content of Mg O, Fe O, Ca O ranging from 15. 12% to 16. 98%, 3. 84% to 5. 34%, 21. 10% to 22. 95%, respectively. The mineral compositions of the Dalaku＇an rock mass are different from those of the mafic-ultramafic cumulates from ophiolites, indicating that the Dalaku＇an rock mass isn＇t a component of ophiolite but a continental intrusion. The mineral compositions of clinopyroxenes indicate that the parent magma belongs to the tholeiite series, which was formed in the continental margin rift during the subduction. There exist favorable conditions for the Cu-Ni sulfide deposit, as shown by the type of the intrusion, mineral chemistry and tectonic setting.