摘要
本文从岩石地球化学特征微观角度，探索巴颜喀拉三叠纪沉积盆地物源区构造背景。据盆地东部阿坝若尔盖、小金马尔康及雅江次级盆地岩屑砂岩宏量、微量、稀土元素地球化学特征，巴颜喀拉三叠纪沉积盆地物源区的大地构造背景在不同时期表现为被动大陆边缘、大陆岛弧、活动大陆边缘和大洋岛弧等。盆地边缘与不同性质的洋壳、陆壳和过渡壳呈不同程度的接触，是造成沉积物多来源。
The Triassic Bayan Har sedimentary basin has spanned the steady subsidence stage during the Early Triassic and the extensional subsidence stage during the Middle Triassic and early and middle Norian stages of the Late Triassic, i.e. the evolution from a starved deep marine basin to filled deep marine basin. Till the late Norian, it began to be uplifted to be an intracontinental intermountainous basin. Moreover the turbidites are widespread in the Aba Zoige, Xiaojin Barkam, Yajiang, Hoh Xil and Jiulong Basins. All this shows the Bayan Har Basin was an open ocean in the hemipelagic and pelagic environments. The major element, trace element and rare earth element geochemistry of the lithic sandstones in the Zagunao, Zhuwo, Xinduqiao, Lianghekou and Yajiang Formations indicates distinct tectonic settings of the provenances such as passive continental margin, continental island arc, oceanic island arc and active continental margin. According to the Dickinson’s Q F L diagram and trace element geochemistry, the principal source of detritus in the Bayan Har Basin lay in the continental island arc. For instance, the fragments in the Lower Bayan Har Group were derived dominantly from the continental island arcs, subordinately from the passive continental margins; those in the Middle Bayan Har Group were derived from the continental island arcs and oceanic island arcs, and those in the Upper Bayan Har Group were derived from the active continental margins and oceanic island arcs. Compared with other basins mentioned in the text, the Bayan Har Basin exhibits the depositional evolution, from east to west and from bottom to top, from the passive continental margins to active continental margins, continental or oceanic island arcs. Since the Bayan Har Basin was in the zone sandwiched between the Qinling Qilian Kunlun microplate and Karakorum Nujiang Lancangjiang Jinshajiang microplate, and is bounded by the southern margin of the Kunlun Mountains and A’nyemaqen faults on the north, by the Garze Litang fault on the southwest and by the Longmenshan Jinpingshan fault and Yangtze landmass on the east, the margins of the basin may well be correlative with the oceanic crust or continental crust of different tectonic features in the course of oceanic continental transition. The palaeocurrents in the Bayan Har Basin point generally to NW SE, i.e. from the Gozha Lake and Heishibei Lake in the west, through Yanghu Lake, Dogaicoringqang Lake, Xijir Ulan Lake, Hoh Xil, Tongtian River and Bayan Har Mountains, to Yajiang River, Xiaojin, Barkam, Aba and Zoige in the east. The variety of tectonic settings has permitted the complexity and multiple sources of the petrochemical compositions.
