Late Mesozoic magmatic arc of continental margin: constraints from detrital zircon U-Pb data, East China Sea

The Late Mesozoic is an important tectonic period for subduction of the Paleo-Pacific slab beneath East Asia and continental tectonic magmatic activities. Sandstones from the Well ECSs611 closely adjoining the Haijiao Uplift from the East China Sea are investigated in order to trace late Mesozoic magmatic arc by U-Pb isotopic dating of detrital zircons from the Oligocene Huagang Formation (1626~1638 m) and the Cretaceous (1638~1689 m) sandstones. Results show that the detrital zircons from the Huagang Formation and the Cretaceous samples are mainly magmatic zircons with some metamorphic ones that formed in two episodes at ~163 Ma and ~120 Ma respectively, registering two late Mesozoic magmatic-metamorphic events. These magmatic zircons from arc-related magmatic source are characterized by low-temperature (556~732℃), enrichment of fluid-mobile U (82×10-6-3412×10-6) and high field-strength Nb depletion (0.6×10-6~13.8×10-6). Compared with the oceanic zircons, these magmatic zircons which formed in two episodes of ~163 Ma and ~120 Ma are characterized by lower Y (371×10-6~2700×10-6) and U/Yb ratio (0.2~6.7). Hence we infer that these magmatic zircons belong to continental zircons. These magmatic zircons are continental rather than oceanic, while other ages from detrital zircons (2.5~2.4 Ga, 1.7~1.6 Ga, 320 Ma and 256~207 Ma) are consistent with key tectonic events undergone by the South China block. It is inferred that the Haijiao uplift zone belongs to eastward extension of South China. The Haijiao-Hupijiao zone as a magmatic arc, together with units of the Fuzhou forearc basin and SW Japan-Taiwan subduction accretionary complex constitutes an outline of late Mesozoic continental margin of East China Sea, formed by the subduction of the paleo-Pacific slab. © 2020, Science Press. All right reserved.