Geochronology, geochemistry and geodynamic setting of Late Cretaceous magmatism and Sn mineralization in the western South China and Tengchong-Baoshan

Two important Sn metallogenic belts are developed in the western South China and the Tengchong-Baoshan regions. The large-scale magmatism and related Sn mineralization in the two belts share many similarities in geochronological and geochemical signatures. The Late Cretaceous intrusions and Sn deposits in the two regions mainly formed in 78. 9 similar to 60. OMa and 108. 0 similar to 74. 1Ma, with peaks of 76. 0 similar to 62. OMa and 98. 0 similar to 82. OMa, respectively and show a younging trend from east to west. The intrusions related to the Late Cretaceous mineralization have typical granitic composition and are characterized by high SiO2 contents, high Al2O3 and K2O contents, slight enrichment in LREE with pronounced negative Eu anomalies, enrichment in Rb, Th and U, and depletion in Ba, Nb, Sr and Ti; they also have initial Sr-87/ Sr-86 ratios ranging from 0. 7038 to 0. 7283 and relatively low epsilon(Nd)(t) values ( -11.6 to -6. 9) and epsilon(Hd)( t) value (- 18. 1 to + 1. 2). All the above features indicate an dominantly crustal origin. A comprehesive review in this paper combined with the regional geological evidence demonstrates that the Tengchong-Baoshan region was controlled by the subduction of the Neo-Tethyan Ocean in the Late Cretaceous, whereas the lithospheric extension in the western South China may have been controlled either by the remote effect of the rollback of the subducted Pacific oceanic plate in the east or by the rollback of the subducted Neo-Tethyan oceanic plate in the west, or else, by a joint action. By comparing the similarities and spatial differences of the ages and geochemical characteristics in the two regions, we suggest a joint Neo-Tethyan Ocean subduction tectonic model : the magmatism and Sn mineralization in the western South China could have been controlled by Tethyan tectonic domain, including the Neo-Tethyan Ocean flat-slab subduction, slab rollback and intracontinental back-arc extension that triggered the asthenosphere upwelling in the western South China, and crustal decompression and melting in the Tengchong-Baoshan regions. This model provides a new insight into the Late Cretaceous cross-regional tectonic setting of the magmatism and Sn mineralization in the western margin of South China and the Tengchong-Baoshan regions.