北羌塘托纳木地区上白垩统阿布山组沉积特征、物源分析及其构造意义

Sedimentary Characteristics, Provenance Analysis and Tectonic Significance of the Late Cretaceous Abushan Formation in Tonamu Area, Northern Qiangtang

羌塘—拉萨碰撞造山作用是青藏高原中生代最为重要的构造事件,羌塘盆地内晚白垩世阿布山组是羌塘—拉萨碰撞造山作用的沉积记录。托纳木地区发育了北羌塘坳陷少有的晚白垩世阿布山组沉积,然而对其形成构造背景和动力学机制尚不清楚。本文通过对托纳木地区阿布山组沉积环境、物源区详细表明,该地区阿布山组下部以冲积扇环境为主,中上部为辫状河环境。砾石成分、古水流、砂岩岩石学、砂岩重矿物、碎屑锆石U-Pb定年等物源综合分析显示中央隆起带和盆地内部均为阿布山组提供物源,结合邻区阿布山组对比,认为研究区物源来自盆地内西南方向下伏沉积、晚三叠世那底冈日组火山岩以及盆地基底,阿布山组沉积受盆地内构造控制。托纳木地区阿布山组物源区特征反映了北羌塘晚白垩世地体内部的逆冲事件,与羌塘—拉萨地体碰撞有关。

The Qiangtang–Lhasa collisional orogeny is the most important Mesozoic tectonic event in the Tibetan Plateau. The Late Cretaceous Abushan Formation in the Qiangtang Basin serves as the sedimentary record of the Qiangtang–Lhasa collision orogeny. There is a rare Late Cretaceous Abushan Formation deposit in northern Qiangtang Depression in Tonamu area. However, the tectonic setting and dynamic mechanism of its formation remain unclear. In this paper, the sedimentary environment and provenance of Abushan Formation in Tonamu area are shown in detail. The comprehensive analysis of the provenance, including the composition of gravel,paleocurrences, sandstone petrology, heavy minerals of sandstone and U-Pb dating of detrital zircons, shows that the central uplift belt and the interior of the basin all provided the provenance of the Abushan Formation.Combined with the comparison of the Abushan Formation in the adjacent areas, it is considered that the provenance of the study area came from the underlying sediments in the southwest of the basin, the volcanic rocks of the Late Triassic Nadiganri Formation and the basement of the basin. Sediments of Abushan Formation are controlled by intra-basin structures. The provenance characteristics of the Abushan Formation in the Tonamu area reflect the thrust event in the Late Cretaceous terrane of the northern Qiangtang and were related to the collision of Qiangtang–Lhasa Terrane.