Abstract:

In this study, we conducted LA-(MC)-ICP-MS U-Pb dating and Hf isotope analysis on detrital zircons from the Nenjiang River floodplain sediments. The results show that the U-Pb ages of 293 detrital zircons can be divided into four major groups, i.e., 2,300-1,746 Ma, 363-331 Ma, 316-260 Ma, and 252-86 Ma. Mesozoic detrital zircons account for 80.9% of the total amount, indicating strong magmatism in the source region during this period. The relative outcrop size of strata (of different ages) is different in the basin: Jurassic-Cretaceous (~72%), Carboniferous-Permian (~13%), Triassic (~8%), Precambrian (~5%), and Cambrian-Silurian (~1%). The Hf isotope composition may reflect the formation and evolution of continental crust in the Nenjiang River catchment. Continental crust in the Nenjiang River basin is mainly produced by juvenile crust formation. The ca. 1,200-400 Ma period likely represents a major continental growth event in NE China, which formed 98.8% crustal components of the present crust, which may be related to the Paleo-Asian Ocean development and subduction. During ca. 400-100 Ma, the Nenjiang Basin may have experienced intense intra-continental crustal recycling. Furthermore, using the formula of recycling ratio, the remelting vs. juvenile crust ratios have been calculated. The Mesozoic zircon have a low remelting ratio and contain about 70% juvenile crust. This phenomenon is related to the partial melting of mantle material caused by subduction of the Mongol-Okhotsk Ocean and Paleo-Pacific Ocean.

Key words: Nenjiang River, detrital zircon, U-Pb age, Hf isotope