Using detrital zircons from river sands to constrain major tectono-thermal events of the Cathaysia Block, SE China

Abstract

Detrital zircons from the Minjiang and Zhujiang Rivers in SE China have been analyzed for U/Pb ages and Lu–Hf isotopic compositions to constrain their provenance and the growth history of the continental crust of the Cathaysia Block. Zircon U/Pb ages show five major populations at 90–250Ma, 400–500Ma, 0.7–1.2Ga, 1.6–2.0Ga and 2.3–2.6Ga. Proterozoic zircons have Hf isotopic signatures consistent with the remelted ancient crust and the involvement of juvenile crust. However, Phanerozoic zircons have Hf isotopic signatures indicative of reworked or recycled ancient crust. Crustal growth rates based on the two-stage Hf model ages of the detrital zircons indicate that 30% and 90% of present crust in the northeastern Cathaysia Block was formed by 2.5Ga and 1.6Ga, respectively, whereas <20% continental crust was formed by 2.5Ga, and 80% by 1.6Ga in the southwestern Cathaysia Block. Therefore, Neoarchean and Paleoproterozoic were two major periods of crustal growth of the Cathaysia Block. Our results also reveal that the tectono-thermal events at ∼370Ma and ∼117Ma may have occurred to the Wuyishan terrane in the northeastern Cathaysia Block. Jurassic zircon grains have Hf isotopic compositions more variable than Cretaceous grains, which may have been derived from different source rocks. The 140–120Ma tectono-thermal events were likely related to the change of the subduction direction of the Paleo-Pacific plate from northward to northwestward at 140Ma. The 112–90Ma tectono-thermalevents may be correlated with the rollback of the subducted paleo-Pacific plate at ∼110Ma.