羌塘盆地安多114道班地区上白垩统阿布山组沉积环境、物源分析及其构造意义

Sedimentary environment,provenance analysis and tectonic significance of the Upper-Cretaceous Abushan Formation in 114 Daoban,Anduo area,Qiangtang Basin

羌塘盆地晚白垩世广泛发育阿布山组陆相粗碎屑岩沉积,然而当前对其沉积环境、物源特征、构造背景尚不清楚,这制约着我们对羌塘-拉萨地体碰撞后羌塘盆地的沉积演化和高原早期隆升的准确认识。为了解决上述问题,本文对安多114道班地区阿布山组的沉积时代、沉积环境、物源特征进行了详细研究。野外观察发现,阿布山组与下伏安山岩和上覆牛堡组均呈角度不整合接触,结合安山岩喷出时代和牛堡组的沉积年龄,限定其沉积时代为晚白垩世;阿布山组中砾石成分和形态结果显示,这些砾石主要为灰岩,且经历的搬运距离较短,为近源堆积。砂岩碎屑成分、重矿物特征、碎屑锆石年龄谱表明,阿布山组的物源主要来自南羌塘坳陷内部和中央隆升带的晚三叠世—侏罗纪地层。对比邻区阿布山组特征,本文认为羌塘盆地晚白垩世陆相红色碎屑岩的沉积与羌塘-拉萨地体持续汇聚作用形成的一系列逆冲推覆活动有关。

Late-Cretaceous continental strata of the Abushan Formation consist mainly of coarse clastic rocks and outcrop widely in the Qiangtang Basin,however,its sedimentary environment,source characteristics and tectonic setting remain unclear.In order to better understand the sedimentary evolution of the Qiangtang Basin and the early Tibetan Plateau uplift history after the Qiangtang-Lhasa collision we conducted detailed investigation into the depositional age,sedimentary environment,and source characteristics of the Abushan Formation in 114 Daoban,Anduo area.Angular unconformities were observed between the Abushan Formation and the underlying andesite and overlying Niubao Formation.Based on this observation,along with the eruption age of andesite and the depositional age of the Niubao Formation,we conclude that the Abushan Formation was deposited during the Late Cretaceous.Gravels of the Abushan Formation indicated a near-source deposition scenario as they mainly consisted of limestone and were transported over a short distance.Combined with geochemical data on sandstone detritus and heavy minerals,along with detrital zircon age spectra,we consider that the Abushan Formation was mainly sourced from Triassic-Jurassic strata in the southern Qiangtang and the central uplift zone.By comparing the stratigraphic characteristics between the Abushan Formation and its surrounding area,we suggest that the deposition of continental red clastic rock during the Late Cretaceous was related to large-scale thrusting in the Qiangtang Basin caused by continued plate convergence in the Qiangtang-Lhasa terranes.