Continental growth during Devono-Carboniferous switching accretionary tectonics: the Katebasu granitoid stock, Central Tianshan, NW China

The Central Asian Orogenic Belt (CAOB) records a critical stage of Phanerozoic continental growth directly related to substantial juvenile additions during accretionary orogenesis. However, the processes and mechanisms of how juvenile continental growth remain controversial. The Central Tianshan Block (CTB) is a crucial part of the Tianshan orogenic belt. It was involved in the subduction—accretion of the western Paleo-Asian Ocean and the final amalgamation of the Tianshan Orogen in the southwestern CAOB. Multiphase late Paleozoic magmatism is recorded in the Katebasu district, forming one of the most critical granitoid stocks that host significant gold mineralization (i.e., Katebasu Au deposit, 89 t Au @ 2.7 g/t) in the CTB. Based on our new U–Pb ages, geochemical and Sr–Nd–Hf isotopic systematics, in combination with previously published datasets from the adjacent regions, we propose that the Katebasu granitoid stock records the regional tectonic switching from compression to extension of the CTB during the Devonian to Early Carboniferous. The compressional tectonic regime produced extensive juvenile granitoid crust. In contrast, subsequent extensional setting was probably related to slab rollback that may have triggered incremental involvement of juvenile mantle components in producing additional continental crust. Such a tectonic model probably plays an important role in the tectonic evolution and crustal growth of the CTB during the late Paleozoic. On a larger scale, such a long-term “rejuvenation” process probably plays a significant role in the generation of widespread juvenile magmatism and continental growth during the formation of the CAOB.