U-Pb and Lu-Hf isotope systematics of detrital zircons from the Songpan-Ganzi Triassic flysch, NE Tibetan Plateau: implications for provenance and crustal growth

摘要

We conducted in situ U-Pb and Lu-Hf isotope analyses of 401 detrital zircons collected from the Songpan-Ganzi Triassic turbidite complex in an attempt to understand the provenance variations of the siliciclastic rocks and the crustal growth history of central China. These detrital zircons exhibit a wide age spectrum with three major peaks at 1.7-2.0 Ga, 750-1050 Ma, and 210-500 Ma. They are dominated by negative ε_(Hf)(t) values with a large range. Synthesis of the zircon U-Pb and Lu-Hf isotopic data indicate that the Triassic Songpan-Ganzi turbiditic succession could have been derived dominantly from the Tibetan terrains + the Kunlun and Qinling orogens. Our samples are characterized by a common, prominent group of Hf crust formation model ages at 0.8-4.1 Ga with a peak at 2.7-3.4 Ga. This fact indicates that (1) Phanerozoic magmatism in central China could have been predominantly products of crustal reworking with insignificant formation of juvenile crust and (2) the Neoarchaean was an important period of continental growth in central China. In addition, our data set also reveal that three widespread tectonothermal events could have occurred in the region during the late Mesoproterzoic, Palaeozoic, and early Mesozoic, respectively.