Mesozoic large magmatic events and mineralization in SE China: oblique subduction of the Pacific plate

摘要

SE China is well known for its Mesozoic large-scale granitoid plutons and ore deposits. In SE China, igneous rocks with intrusion ages between 180 and 125 Ma generally become progressively younger towards the NE. More specifically, 180–160 Ma igneous rocks are distributed throughout a broad area, with mineralization ranging from Cu–Au and Pb–Zn–Ag toW–Sn; 160–150 Ma plutons are present mainly in the Nanling region and are associated with the large-scale W–Sn mineralization; younger igneous rocks occur in the NE area that has many fewer deposits. These can be plausibly interpreted as reflecting a southwestward subduction followed by a northeastward rollback of a subducted oceanic slab, in rough agreement with contemporaneous drift of the Pacific plate. Consistent with this scenario, SE China contains three Jurassic metallogenic belts distributed systematically from NE to SW: (1) a Cu–(Au) metallogenic belt in the NE corner of the South China Block, represented by the Dexing porphyry Cu deposits; (2) a Pb–Zn–Ag metallogenic belt in the middle, represented by the Lengshuikeng Ag and Shuikoushan Pb–Zn deposits; and (3) the famous Nanling W–Sn metallogenic belt in the SW. The distribution of these metallogenic belts is analogous to those in South America where Fe deposits are distributed close to the subduction zone, followed by porphyry Cu–Au deposits and Pb–Zn–Ag deposits in a medial zone, and Sn–W deposits distant from the trench. Inasmuch as quite a few late Mesozoic Fe deposits occur in the Lower Yangtze River Belt to the NE of the Cu–Au deposits in SE China, the distribution of late Mesozoic deposit belts in SE China is identical to that in South America. Therefore, southwestward subduction of the Pacific plate and the corresponding slab rollback are proposed here to explain the distributions of the late Mesozoic (180–125 Ma) magmatism and the associated metallogenic belts in SE China.