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Age,geochemistry and tectonic setting of Buqingshan ophiolites,North Qinghai-Tibet Plateau,China

I.Pospelov  O.Astrakhantsev  N.Chamov  
【摘要】:正The Buqingshan ophiolite complex is a sector of the A'nyemaqen ophiolite belt in the East Kunlum southern marginal suture zone in the northern part of the Qinghai-Tibet Plateau.The WNW-trending ophiolite complex consists of pretaperidetic,diabase,pillow basalt, massive basalt and pelagic sedimentary rocks including radiolarian chert.We have deter(?) that Early Paleozoic and Early Carboniferous-Early Permian ophiolites are present in this ophiolite complex that were pre(?)us(?)y thought of Permian-Middle Triassic age. A zircon U-Pb age of 467.2±0.9 Ma for gabbro,and a Rb-Sr isochron age of 481±130Ma for diabase and gabbro have been obtained from the Early Paleozoic ophiolite slice,and Middle-Late Ordovician acritarchs have been found in the melange matrix that envelopes the sliver.We interpret the first two ages to represent the formation age of the ophiolite.(?)ranodiofite- tonalite plutons with a zircon U-Pb age of 402±24 Ma intrude the slice.Early Carboniferous-Early Permian radiolaria(?)s have been discovered in cherts and argillaceous cherts in the second ophiolite slice.Geochemistry indicates that metaperidotites in th first slic(?) rensent a depleted ocean lithosphere mantle.Most mafic rocks in the Early Paleozoic ophiolite are of N-MORB type with sma(?) amount of T-MORB,and they resulted from the magma from the depleted oceanic lithosphere mantle with little crustal contamination.The(?)asa(?)s in the Early Carboniferous-Early Permian ophiolite have similar characteristics to the mafic rocks and also show DUPAI an(?)maly and a mixed source of DMM and EMⅡ.The original formation environments of the two-stage ophiolites are both mid-oc(?) ridges.These lines of evidence suggest that a mature Early Paleozoic Kunlun-Qilian-Qinling ocean basin and a mature Paleote(?)hyan ocean basin once existed in the study area.

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