上扬子西南盐源盆地早三叠世物源体系及构造意义

晚古生代末期至早中生代期间，上扬子西部边缘地区经历了峨眉山大火成岩省构造岩浆热事件和与古特提斯洋闭合相关的三江造山带形成事件，导致康滇古陆两侧形成了独特的盆山格局和沉积模式.由于目前人们对盐源盆地早三叠世青天堡组的物源与构造背景了解不多，故以盐源、盐塘剖面为代表，对青天堡组碎屑岩进行了砂岩组分、全岩地球化学和碎屑锆石年代学分析.结果显示，盐源盆地下三叠统青天堡组物源来自于近源搬运的火山岩，青天堡组与峨眉山大火成岩省的高钛玄武岩具有一致的元素组合配分模式，青天堡组锆石谐和加权平均年龄为261±16 Ma，与峨眉山大火成岩省形成的地幔柱活动时期一致.上述结果表明早三叠世盐源盆地青天堡组物源为其东侧的峨眉山大火成岩省，扬子西部三江造山带可能并没有为盐源盆地提供物源，上扬子西南边缘地区早三叠世时期仍然为被动大陆边缘沉积. 

Provenance of Early Triassic in Yanyuan Basin,Upper Yangtze and Its Implication for the Tectonic Evolution

The tectono-magmatic thermal event of Emeishan Large Igneous Province (ELIP) and the formation of Sanjiang Orogen caused by closure of Paleo-Tethys ocean along the western margin of the Upper Yangtze area during Late Paleozoic to Early Mesozoic shaped the unique pattern of basin-mountain system. For lack of cognition about the provenance and tectonic settings of Qingtianbao Formation in Yanyuan area, southwestern Sichuan, detrital compositions, major, trace elements and detrital zircon isotope ages of clastic rocks from Yantang section were tested and analyzed. The detrital components of Sandstone in Yanyuan region is volcanic clastic mainly and suggests that the provenance of Early Triassic strata was from a nearly source of volcanic rock, detrital zircons yield U-Pb ages of ca. 261 Ma is consistent with the Emeishan mantle plume activity event and the geochemical characteristics of sandstone is similarity to those High Ti basalt of Emeishan LIP. Combined with the research findings of sedimentary and palaeo-geography in Yanyuan area, we suggest that the provenance of Qingtianbao Formation in Yanyuan region came from the Emeishan LIP, but may not came from the Sanjiang Orogen. Southwestern Upper Yangtze area was still a passive continental margin.