Characteristics of Neoproterozoic—Early Mesozoic multiphase orogenic activities of eastern Jiangnan Orogen

Abstract: The Jiangnan Orogen is a suitable region for deciphering Neoproterozoic to Early Mesozoic multiphase orogenic activities of the South China Block because it is far away from the Late Mesozoic active continental margin. Based on a comprehensive analysis of such factors as deposition, magmatism, structural deformation and geochronology, the authors summarized the features of Neoproterozoic, Early Paleozoic and Early Mesozoic orogenies in the eastern Jiangnan Orogen. The eastern Jiangnan Orogen underwent southern and northern subductions as well as two stages of collisions in Neoproterozoic. In 880-860 Ma of the early Neoproterozoic period, arc-continent collision between the Shuangxiwu island arc and the southeastern margin of Yangtze Block induced the formation of 880-860 Ma light granites, high-pressure blueschist, NNE-striking fold-and-thrust structures and retro-arc foreland basins. Southward subduction along the northern margin of Yangtze Block commenced at about 850 Ma. This subduction resulted in the closure of back-arc basin and final collision between the Yangtze and Cathaysia blocks, and triggered nearly EW-striking fold-and-thrust structures, ductile deformation and peraluminous granodiorites in the eastern Jiangnan Orogen. The eastern Jiangnan Orogen started to collapse and rift at about 810 Ma, and produced 805-750 Ma granites, felsic volcanic rocks, mafic dikes and rift basins. Early Paleozoic orogeny occurred in the southern area of the Wanzai-Nanchang-Jingdezhen-Shexian fault zone within the Jiangnan Orogen. This orogeny led to the formation of nearly EW-striking top-to-the north thrusting, NNE-striking positive flower structures and post-orogenic nearly EW-striking dextral shear zones. The Early Mesozoic orogeny brought about NNE-striking fold and thrust structures and granites, which established the basic features of the present eastern Jiangnan Orogen.