Significant crust remelting and accompanied continental uplift during contraction of the amalgamation of world's largest Phanerozoic accretionary orogen (Altaids) with North China Craton

  The Altaids, (also termed as Central Asian Orogenic Belt, CAOB), world’s largest Phanerozoic accretionary orogen, is characterized by multiple collages of juvenile crust, and whether significant tectonic contraction occurred or not during its amalgamation with old continents on its south is unclear. Here, we present zircon U-Pb-Hf and whole-rock geochemical study on middle-late Permian high silica granites in Siziwangqi area of the northern margin of North China Craton (NCC). These rocks from the batholith were formed at ~262-267 Ma, and those from adjacent or individual stocks at ~255-257 Ma. All these granitic rocks were mainly derived from late Archean to Mesoproterozoic rocks of the NCC and similar cases documented commonly along the northern margin of the NCC, indicating a widespread crust-reworking there. Together with coeval compressional structures, accompanying sedimentary records and continental uplift there, this crust-reworking probably resulted from crust shortening by intensive tectonic contraction there. We propose that this tectonic contraction was caused by a collisional event related to closure of the Paleo-Asian Ocean (PAO), supported by: (1) rock change with significant decrease of arc-related magmatism in the northern NCC at ~250-270 Ma, (2) roughly coeval mixing of the Tethyan and Boreal realm fauna of marine strata in the southern CAOB, (3) disappearance of marine strata replaced by continental strata there after ~260 Ma, and (4) occurrence of significantly closer paleolatitudes (~0-5°) between the North China and Mongolia collages after ~260 Ma. Comparatively, the wide CAOB accretionary zone has insignificant contraction, commonly occurred in accretionary orogens. We infer that such difference is due to different crust architecture resulted from different directions of subduction of the PAO.

  This research was financially supported NSFC Project (42102260), Hong Kong RGC GRF (17307918), and HKU Internal Grants for Member of Chinese Academy of Sciences (102009906) and for Distinguished Research Achievement Award (102010100), Fundamental Research Funds for the Central Universities, CHD (300102272204), Croucher Chinese Visitorship (2022-2023) from Croucher Foundation, and the Youth Innovation Team of Shaanxi Universities.