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在青藏高原腹地,二叠纪火山岩分布于唐古拉山东段,古地理上位于北羌塘盆地东缘。对唐古拉山东段莫云地区中二叠世栖霞期尕笛考组火山岩的主量元素、微量元素和Sr-Nd同位素进行了分析。岩相学和地球化学指标显示二叠纪火山岩为玄武岩,该套岩石低SiO2、MgO、K2O和Mg#值(0.39～0.48),富Na2O、TFeO、TiO2、P2O5含量,富集LREE和高场强元素(Nb、Ta、Zr、Hf、P、Ti),(La/Yb)N=14.89～23.23,(Gd/Yb)N=2.30～3.58,Eu异常不明显(δEu=0.76～0.99),具有明显的Th正异常和K、Sr负异常,显示与板内碱性玄武岩相似的地球化学特征;同位素组成以低(87Sr/86Sr)i(0.7033～0.7039)、高εNd(t)(+4.2,t=271Ma)为特点,反映岩浆源区既有亏损地幔源(DMM)又有富集地幔源(EMⅠ)的双重属性。岩浆起源可能与地幔柱诱导的软流圈上涌导致含石榴子石橄榄岩的岩石圈地幔部分熔融有关。莫云玄武岩形成于板内伸展环境(初始裂谷),具有主动裂谷作用性质。
In the hinterland of the Qinghai-Tibet Plateau, Permian volcanic rocks are distributed in the eastern segment of the Tanggula Mountains and are located on the eastern margin of the North Qiangtang Basin in paleogeography. The main elements, trace elements and Sr-Nd isotopes of the Qidisaoxi volcanic rocks in the Qixiaian Period in the Moyun area, eastern Tanggula Mountain, are analyzed. The lithofacies and geochemical indicators show Permian volcanic rocks are basalts. The rocks have low contents of SiO2, MgO, K2O and Mg # (0.39-0.48), rich in Na2O, TFeO, TiO2, and P2O5, (La / Yb) N = 14.89 ~ 23.23, (Gd / Yb) N = 2.30 ~ 3.58, and Eu anomalies are not obvious (δEu = 0.76 ~ 0.99) With obvious Th positive anomaly and negative K and Sr anomalies, indicating similar geochemical characteristics as the alkaline basalt in the plate. The isotopic composition of the isotopes is characterized by low (87Sr / 86Sr) i (0.7033 ~ 0.7039), high εNd (t) (+ 4.2 , t = 271Ma), reflecting the dual attributes of both depleted mantle source (DMM) and enriched mantle source (EMⅠ) in the magma source region. The origin of the magma may be related to the mantle plume-induced upwelling of the asthenosphere resulting in the partial melting of the lithospheric mantle containing garnet-bearing peridotites. Moyun basalts are formed in extensional environments (initial rifting) with active rifting.