中文摘要：

目前对青藏高中部的蛇绿岩类型、形成环境及其深部地幔源区特征还缺乏很好的约束。在区域地质调查基础上，本文展示了青藏高原中部龙木错双湖缝合带嘎错玄武岩、班公湖-怒江缝合带多玛、塔仁本玄武岩及那曲盆地西侧中生代玄武岩的单斜辉石ArAr测年、锆石SHRIMP定年和地球化学及Sr，Nd，Pb同位素数据，以约束形成这些玄武岩的时代、构造环境和地幔源区特征。目前的数据表明：①羌塘双湖嘎错枕状玄武岩单斜辉石的中温坪年龄为232．5=2．4Ma，可能指示嘎错玄武岩浆活动发生于中三叠世晚期，班公湖-怒江缝合带多玛枕状玄武岩、塔仁本玄武岩浆活动时代大约在早白垩世中晚期（110Ma左右）；②在这些蛇绿混杂岩带中的玄武岩显示OIB而不是MORB型地球化学特征，双湖嘎错玄武岩的地球化学特征介于峨眉山高Ti玄武岩与夏威夷碱性玄武岩之间；中晚三叠世那曲嘎加组玄武岩的地球化学特征非常类似于夏威夷碱性玄武岩；班公湖怒江缝合带内的早白垩世多玛玄武岩和塔仁本玄武岩的地球化学特征在很大程度上可比于夏威夷碱性玄武岩；⑧双湖嘎错OIB型玄武岩可能形成于以增生楔为基底的裂谷环境而不是以洋壳为基底的大洋板内环境，那曲嘎加组OIB型玄武岩很可能形成于以弧内-弧前沉积物为基底的陆棚-陆坡环境下的裂谷背景，塔仁本和多玛OIB型玄武岩形成于以洋壳为基底的洋岛环境，这表明班公湖怒江洋壳在大约110Ma时尚未彻底消亡，可能暗示班公湖怒江洋盆的关闭时间明显晚于晚侏罗世-早白垩世早期闭合的早期认识；①地球化学指标显示青藏高原中部中生代玄武岩未受到地壳物质或很少受到陆下岩石圈物质改造，一些相对新鲜样品的Nd，Pb组成似乎可以用来代表其地幔源区的成分特点，其高^206Pb／^204Pb比值（〉18．5）指示羌塘双

英文摘要：

Rock-type, tectonic setting and nature of mantle source region for the ＂so-called＂ ophiolite in central Qinghai-Tibetan Plateau is poorly understand at present. We present Ar-Ar dating of clinopyroxene, SHRIMP zircon dating, geochemical and Sr-Nd-Pb isotopic results for the basalts from Gaco village in Longmu CoShuanghu ophiolitic m61ange zone, Duoma and Tarenben villages from Bangong Co-Nujiang suture zone and western Nagqu basin in central Qinghai-Tibetan Plateau in order to constrain their age, tectonic setting and nature of mantle source region. Present data show that the basaltic magmatism in Gaco village, Shuanghu transitional between Emeishan high-Ti basalt and Hawaiian alkaline basalt, the Mid-Late Triassic basalts in Gajia Formation from western Nagqu basin are closely geochemically similar to Hawaiian alkaline basalt and the Early Cretaceous basalts in Duoma, Tarenben villages from Bangong Co-Nujiang suture zone are largely comparable to those of Hawaiian alkaline basalt. With consideration of geochemical constraint and sedimentary sequence, we propose that Gaco OIB-type basalts may form at a rift setting constructed on accretionary wedge rather than an intra-plate on oceanic crust, and that Gajia Formation basalts are probably erupted at a rift setting on continental shelf-slope floored by intra-and fore-arc basin sediments. Duoma and Tarenben basalts in Bangong Co-Nujiang suture zone are interpreted to have formed in an oceanic island setting, which may indicate that the Bangong Co-Nujiang oceanic crust is still presented at about 110 Ma, implying that the closure time of this ocean is considerably lag behind the Late Jurassic-Early Cretaceous proposed by previous works. Geochemical signatures indicate that crust contamination and sub-continental lithospheric mantle material played insignificant role in the generation of the Mesozoic basalts in central Qinghai-Tibetan Plateau, it is therefore possible that the Nd, Pb isotopic compositions of some relative fresh samples can be used to represent the