Westward Subduction Of Paleo-Pacific Plate Research Articles

Diverse and multistage Mo, Au, Ag–Pb–Zn and Cu deposits in the Xiong'er Terrane, East Qinling: From Triassic Cu mineralization

The Xiong'er Terrane is one of the representative regions in East Qinling Orogenic Belt. Various polymetallic deposits have been discovered in the Xiong'er Terrane, such as porphyry Mo, carbonatite-hosted type Mo, quartz-vein type Mo, breccia-pipes type Au and orogenic-type Au, Ag–Pb–Zn deposits, indicating that diverse significant mineralization occurred in the Xiong'er Terrane. Recently, numerous Cu deposits have been observed in the Xiong'er Terrane. Xianglugou is a quartz vein-type copper mineralization which was discovered in Xiayu district, southern of the Xiong'er Terrane. Four chalcopyrite samples from Xianglugou yield Re–Os isochron age of 230±31Ma (2σ, MSWD=0.8). This is the first evidence for Triassic Cu mineralization in the Xiong'er Terrane. This not only shows the Xiong'er Terrane contains considerable Mo, Au and Ag–Pb–Zn reserve, but also indicates that there is a great potential of Cu mineralization. The discoverable Cu mineralization can further emphasize the significance of the widespread Triassic mineralization and widened exploration ideas and goals in the future in the Xiong'er Terrane.The Xiong'er Terrane experienced three polymetallic mineralization events including Paleoproterozoic, Triassic and Late Jurassic to Early Cretaceous deposits during the Qinling Orogen evolution. These metallogenic events may be related to multiple tectonic events. The Paleoproterozoic mineralization was associated with the continental outgrowth occurred along the southern margin of the North China Craton before 1760Ma. The Triassic Cu mineralization may be associated with the northward subduction of the North Qinling Orogen beneath the Huaxiong Block during the collision between North China Craton and Yangtze Craton. Late Jurassic to Early Cretaceous mineralization perhaps caused by decompressional extension of the Qinling Orogenic belts and the North China Craton intense destruction and lithospheric thinning, which is now generally related to the westward subduction of paleo-Pacific plate.

Late Mesozoic–Early Cenozoic deformation history of the Yuanma Basin, central South China

The Yuanma Basin, situated in central South China with more than 800km far away from the active plate boundaries, is a key region in deciphering the Late Mesozoic–Early Cenozoic tectonic evolution of South China. Based on a field analysis of fault–slip data collected from different rock units, we document polyphase tectonic stress fields and address the changes in the orientation of the principal stresses, and finally establish a five-phase stress evolution of the basin during the Late Mesozoic–Early Cenozoic. The earliest one with E–W compression and N–S extension occurred in the Mid–Late Jurassic and resulted in regional folding and west-directed thrusting along the eastern margin of the basin. This deformational event constrains the timing of the significant intracontinental orogeny in South China to be Mid–Late Jurassic. The subsequent NW–SE extensional regime was responsible for the initial opening and sedimentary infill of the basin during the earliest Cretaceous, which occurred coevally with the extensive Early Cretaceous magmatism, volcanism and extensional doming in South China. The tectonic regime then changed, in the late Early Cretaceous, to a compressional one with NW–SE compression and NE–SW extension, causing the inversion of this extensional basin. This compression affected the whole South China, leading to an apparent magmatic quiescence at ~108–117Ma and sinistral strike–slip faulting on the NNE-trending faults. The N–S extension prevailed in the Late Cretaceous, and activated the east-trending normal faults that controlled the Late Cretaceous subsidence. This extensional phase seems to have lasted through the Early Paleogene and ended in the Late Paleogene by a compressional regime with NE–SW compression and NW–SE extension, as attested by the stratigraphic unconformity at the base of the Neogene in the Jianghan Basin. The temporary evolution of these tectonic stress fields documented in the Yuanma Basin provides a new insight into the influences of different plate tectonics exerting on the South China Block over the Late Mesozoic to Early Cenozoic time. We infer that the Yuanma Basin was influenced, in the Middle Jurassic–Early Cretaceous, by the process of westward subduction of paleo-Pacific plate; and in the Late Cretaceous–Early Paleogene by a combined effect of the subduction along the west pacific margin and in the Tethyan domain; and finally in the Late Paleogene by the far-field effects of India–Asia collision.