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班公湖-怒江缝合带内的尼玛盆地在青藏高原形成时记录的地质信息,有助于恢复其构造古地理从而为高原隆升过程提供沉积学证据,且目前对盆地北部坳陷古近系牛堡组的研究尚属薄弱.利用碎屑岩岩石学、锆石年代学、重矿物分析等方法对牛堡组进行了物源分析并对盆地构造演化进行了深入讨论.研究显示,早白垩世-古近纪,随着地壳缩短、逆冲断层及造山带发育,盆地北部演化为受构造活动控制的独立坳陷;北部坳陷牛堡组为南北双向物源,北部物源的母岩成分主要为以早白垩世虾别错花岗岩为代表的酸性岩浆岩,南部物源的母岩成分以沉积岩(硅质岩等)和基性岩浆岩为主;碎屑锆石存在105~134Ma、500~550Ma、700~900Ma、1 700~2 100Ma及ca.2 500Ma年龄峰值,其中105~134Ma年龄是对班公湖-怒江洋壳俯冲在周边地体引发的岩浆事件的响应,进一步证实牛堡组碎屑岩的物源来自北部坳陷的南北两侧地体.挤压及逆冲变形决定了盆地北部坳陷的古地理特征,沉积过程及物源与区域隆升、侵蚀和岩浆活动联系密切.
The geological information recorded in the formation of the Tibetan Plateau during the formation of the Nimu Basin in the Bangong-Nujiang suture zone helps to restore the tectonic paleogeography and provide sedimentary evidence for the uplift of the plateau. At present, The study of Niubebao Formation is still weak.The source analysis of Niubebao Formation and the tectonic evolution of the basin have been carried out by using the methods of clastic rock petrology, zircon geochronology and heavy mineral analysis etc. The study shows that early From the Cretaceous to the Paleogene, the northern part of the basin evolved into an independent depression controlled by tectonic activity as the crust shortened, thrust faults and orogenic belts developed. The Niupu Formation in the northern depression is a north-south two-way source and the source of the north The rock components are mainly acidic magmatic rocks represented by the Early Cretaceous shibiscissima granite. The parent rock components of the southern provenances are mainly sedimentary rocks (siliceous rocks, etc.) and basic magmatic rocks; detrital zircons are present at 105-134 Ma , 500 ~ 550Ma, 700 ~ 900Ma, 1 700 ~ 2 100Ma and ca. 500Ma age peaks, of which 105 ~ 134Ma ages were the response to the magmatic event triggered by the subduction of the Bangong Lake-Nujiang oceanic crust in the surrounding area, further confirming The source of the Niubebao clastic rocks comes from the north Depression north and south sides of the body. Thrust deformation and extrusion determine the geographical features of ancient northern depression of the basin, the deposition process and provenance links with regional uplift, erosion and magmatic activity closely.