Late Jurassic-Cretaceous Sedimentary Response To Collision Process In Middle Bangonghu-Nujiang Suture

Bangonghu-Nujiang Suture Zone (BNSZ) is an important tectonic zone in the Qinghai-Tibet Plateau. The Bangonghu-Nujiang Suture Zone (belt) and Qiangtang Basin recorded the formation and evolution of Tethys in the Mesozoic times. It is one of the ideal areas to study the ocean-land conversion and basin-range coupling. Based on the theory of collision tectonics, orogenic blet and basin analysis, this paper studies the sedimentary response of collision process in the mid-Bangonghu-Nujiang Suture Zone.Firstly, the stratigraphic sequence has been divided into Late Jurassic Anduo and Bangai Formations, Early Cretaceous Dongqiao Formation, Late Cretaceous Abushan Formation in ascending order, and a late Mesozoic litho-stratigraphic framework has been established in the Anduo area.Secondly, sedimentary facies have been studied from the sequence. In the Anduo Formation, fan delta, braided river, alluvial fan, pyroclastic debris flow, lahar and lava flow are illustrated. In the Bang'ai Formation, carbonate open platform, restricted platform, evaporate platform, lagoon and clastics tide flat are recognized. In the Dongqiao Formation, alluvial fan-fan dealt, restricted sea, coastal-shallow lake and delta are discussed. In the Abushan Formation, alluvial fan, braided river and shallow salt lake facies are recognized. According to the sedimentary facies, the sediments of Anduo Formation in the basin mostly came from the island arc belt in the south of basin. The detrital composition and the geochemistry characters imply that the island arc is the tectonic background of the source area. The sediments of Dongqiao Formation in the basin came from two ways; the Abushan sediments were from adjacent of the orogenic belt. Based on sequence stratigraphy, late Mesozoic strata have been divided into three two-order megasequences and eight or nine three-order cyclic-sequences. The Late Jurassic-Early Cretaceous tectonic sequence includes 3 or 4 three-order sequences. The Early Cretaceous tectonic sequence includes 3 or 4 three-order sequences. The Late Cretaceous tectonic sequence includes 3 or 4 three-order sequences. These sequences show a stratigraphic response to the collision processes.The island arc belt is composed of volcanic rocks of Anduo Formation. The volcanic rock sequence belongs to a basic -intermediate -acidic rock series. Geochemistry analysis...