The generation and reworking of continental crust during early Paleozoic in Gondwanan affinity terranes from the Tibet Plateau

The central-south Tibet Plateau represents an important part of the northern segment of the Gondwana supercontinent during the early Paleozoic. Here, we statistically analyze the Lu-Hf isotopic data of Phanerozoic granitoids from this area, with a view to gain insights on the early Paleozoic geotectonic evolution of the Gondwana northern margin. The zircon Lu-Hf data from Phanerozoic granitoids, combined with the field evidence, provide insights into the involvement of Paleo-Mesoproterozoic crustal materials in the Tibet Plateau. The variable zircon Hf isotopic data, dominated by negative epsilon(Hf)(t) values, of the early Paleozoic granitoids reveal the temporal and spatial heterogeneities of Paleo-Mesoproterozoic continental crust. Our results suggest that crust formation occurred at similar to 1.7 Ga, similar to 1.4-1.6 Ga, similar to 1.1-1.3 Ga, similar to 0.8 Ga, similar to 0.5-0.6 Ga, and similar to 0.3 Ga. A large volume of early Paleozoic juvenile crusts in the Lhasa and Himalaya terranes are identified, whereas the south Qiangtang terrane and east Tibet are dominated by ancient crust. In addition, the reworking of ancient crust plays an important role throughout the Phanerozoic evolution of the Tibet Plateau. Reworking of old crust occurs mainly in advancing accretionary orogens and internal collisional orogens. However, the subduction-related magmatism resulted in marked excursions of zircon Hf isotopic composition toward depleted mantle-like features, which produced positive epsilon(Hf)(t) values. Postcollisional magmatism associated with delamination, orogenic collapse, or lithospheric extension leads to melting of the underthrust continental fragment, thereby driving zircon epsilon(Hf)(t) to negative values. In addition, the collapse and eventual rifting of the continental crust are generally accompanied by relatively minor volumes of mafic magmatism and crustal generation, which is consistent with our inferences. Therefore, we concluded that the Cambrian-Ordovician magmatic rocks from the central-south Tibet Plateau might have developed within a postcollision extensional, or even an eventual rift setting, following the Pan-African orogenesis.