青海省阿尼玛卿带布青山蛇绿混杂岩的地球化学性质及形成环境

Geochemistry and Formation Environment of the Buqingshan Ophiolite Complex, Qinghai Province, China

布青山蛇绿混杂岩位于阿尼玛卿带西段,它是由早古生代和早石炭世—早二叠世两期蛇绿岩组成的复合蛇绿混杂岩带。蛇绿岩中的变质橄榄岩以方辉橄榄岩为主,高镁,∑REE是球粒陨石的0.2～0.65倍,HREE是球粒陨石的0.28～0.32倍,属亏损的大洋岩石圈地幔。早古生代蛇绿岩中辉长岩、辉绿岩和玄武岩等镁铁质岩主要具N-MORB性质,少量具T-MORB性质。早石炭世—早二叠世蛇绿岩中玄武岩也主要具N-MORB性质、少量具T-MORB性质。它们均形成于洋中脊环境。本区曾存在成熟的早古生代洋盆和古特提斯洋盆,有更复杂的构造演化史。

The Buqingshan ophiolite complex is located in the western sector of the A'nyemaqen ophiolitic and tectonic melange belt, East Kunlun orogen, Qinghai Province. It is a composite ophiolitic melange belt, consisting of Early Palaeozoic ophiolite and Early Carboniferous-Early Permian ophiolite. The metaperidotites of the ophio-lites are mainly harzburgites, with high Mg, the 2REE being 0. 2-0. 65 times that of chondrite, HREE 0. 28 -0. 32 times that of chondrite, and belong to the depleted oceanic lithosphere mantle. The mafic rocks of the Early Palaeozoic ophiolite are mainly N-MORB, minorly T-MORB. The pillow lavas and massive basalts of the Early Carboniferous-Early Permian ophiolite are also mainly N-MORB, minorly T-MORB. They are all formed in oceanic ridge environments. The mature Palaeozoic oceanic basin and Palaeotethyan basin once existed in this area. This indicates that the A'nyemaqen and the southern ophiolite and tectonic melange belt has a more complex evolution history than hitherto considered.