Late Mesozoic Paleo-Pacific Plate “scissors-like” subduction: Insight from the magmatism in the Gan-Hang Belt, Southeast China

Abstract

Abstract Though it is widely accepted that the Paleo-Pacific Plate has a subducted beneath the eastern Asian continent, controversy still exists regarding the initial timing and geodynamic model of the subduction. In this contribution, we report new geochronology and geochemical data of granitic plutons within the Gan-Hang Belt in Southeast China. The Damaoshan pluton yields zircon U-Pb ages of 139.60 ± 0.69 Ma and 133.90 ± 1.70 Ma, and the Qianshan and Fenglonggu plutons are dated at 135.70 ± 1.30 Ma and 135.33 ± 0.93 Ma, respectively. The Hecun and Huangtuling plutons yield ages of 157.85 ± 0.77 Ma and 167.10 ± 7.50 Ma, respectively. The Damaoshan pluton has an obvious A-type geochemical signature in terms of major and trace element compositions, such as high K2O + Na2O contents (average 8.46 wt%) and FeOT/MgO ratios (average 10.29). The low CaO/Na2O ratios but high Al2O3/TiO2 (average is 110.05), Rb/Ba (average is 9.14), and Rb/Sr (average is 22.53) ratios indicate a derivation from pelite-derived melt. Meanwhile, we also studied the Mesozoic adakites related to magmatic ore formed during a compressive tectonic setting as well as the later bimodal dikes and A-type granitic plutons formed during the extensional tectonic setting in the Gan-Hang Belt. The multiphase qualitative plutons with geochemical characteristics of the adakitic and island arc types (175–150 Ma) related to the northwestward subduction of the Paleo-Pacific Plate, several bimodal dikes, and A-type granitic plutons (135–123 Ma) related to the subducted slab roll-back are found within the Gan-Hang Belt. All of these plutons show a decreasing trend of isotopic ages from the inland area to the coast, from SW to NE. We propose that the distribution pattern of these plutons in Southeast China was controlled by a scissors-like subduction and slab roll-back of the Paleo-Pacific Plate, which occurred roughly from SW to NE along the continental margin approximately during the Middle Jurassic to the Early Cretaceous.