Stratigraphic Framework Of The Northern Yangtze Foreland Basin In The Early-middle Jurassic:A Record Of Continent-continent Collision

To discuss the collision process between the Yangtze and North China-Qinling-Dabie complex plates during the Early-Middle Jurassic,in this study we synthesize the Early-Middle Jurassic foreland basin of the northern Yangtze plate in terms of characteristics of basin-filling successions during Early and Middle Jurassic time,stratigraphic correlation frameworks,paleogeographic reconstruction and evolution history and provenance analysis of the foreland basins and so on.The northern Yangtze foreland basin system was formed during the Mesozoic continental collision between the North China and South China plates along the Mianlue suture.Complete oceanic closure along the Mianlue suture during the Early-Middle Jurassic(201-164Ma)produced an extensive east-west-trending molasse basin with river,deltaic and lake deposits in response to the intracontinental thrust deformation in the adjacent southern Qinling-Dabieshan foreland fold-and-thrust belt.A gravelly alluvial fan depositional system developed in the lower part of the Baitianba Formation and progressively evolved into a meandering river fluvial plain and lake systems southward during the Early Jurassic.The alluvial fan conglomerates responded to the initial uplift of the southern Qinling-Dabieshan foreland fold-and-thrust belt after the oblique collision between the Yangtze and North China plates during the Late Triassic.The Qianfoya Formation(lower Middle Jurassic)mainly developed from shore-shallow lacustrine depositional systems.The Shaximiao Formation(upper Middle Jurassic)predominantly consists of thick-bedded braided river delta successions that serve as the main body of the basin-filling sequences.The upward-coarsening succession of the Shaximiao Formation was controlled by intense thrusting in the southern Qinling-Dabieshan foreland fold-and-thrust belt.The Early-Middle Jurassic foredeep depozone of the northern Yangtze plate was characterized by asymmetric wedge-shaped style.LA-ICP-MS U-Pb ages of detrital zircon show that the sediments of Middle Jurassic are derived from tectono-magmatism related to intracontinental deformation stage of the Qinling-Dabieshan orogenic belt,collisional-magmatism of the Mianlue suture zone related to the Yangtze plate subducted underneath the Qinling-Dabieshan microplate,collisional-magmatism of subdubtion between the South Qinling and North Qinling,continental rift of the northern Yangtze Craton and Rodinia supercontinent,and crystalline basement of the northern South China plate.Paleogeographic reconstructions indicated an extensive east-west foredeep depozone along the foreland fold-and-thrust belt during the Middle Jurassic(174-163Ma)that was nearly 150 km wide.The depozone extended westward to the Longmenshan and further east to the northern middle Yangtze plate.The northern Yangtze foreland basin was almost completely buried or modified by the subsequent differential thrusting of Dabashan and its eastern regions(Late Jurassic to Cenozoic).The northern Yangtze basin experienced two stages of evolution.The basin originated during the Early Jurassic(201-174Ma)and substantially subsided during the Middle Jurassic(174-164Ma).The extensive east-west foreland basin of the northern Yangtze plate indicates that the Yangtze plate face-to-face collided with the Qinling-Dabie-North China complex plates during the Early-Middle Jurassic after the Late Triassic oblique subduction,which provides insight regarding the dynamic continental background of the foreland basin formation of the northern Yangtze plate.