Abstract:
Objective Aiming at the scientific problems that the Late Triassic tectonic−magmatic evolution mechanism of the northern margin of the North China Plate is still unclear, and there is a lack of direct petrological evidence for crust−mantle interaction and petrogenic background in the continental collage stage after the closure of the Paleo−Asian Ocean, this paper studies the petrogenesis of the Dawopu granodiorite in Kaiyuan, northern Liaoning, to constrain the timing of magmatism and reveal its petrogenesis and tectonic setting.
Methods A systematic study of petrography, major and trace element geochemistry, zircon U−Pb dating and Lu−Hf isotopic analysis was carried out on the pluton.
Results Zircon U−Pb dating shows that it was formed in the middle Late Triassic (222~221 Ma). Geochemically, the rocks are characterized by high SiO2 (65.76%~67.65%), Al2O3(15.97%~16.42%), Na2O(4.54%~4.90%), Sr(368.6×10−6~813.2×10−6), low Y (6.9×10−6~13.9×10−6) and Yb (0.83×10−6~1.17×10−6), and high Sr/Y ratios (53.6–74.0), typical of adakitic rocks. Zircon Hf isotopic analyses yield εHf(t) values of 9.51~12.24, indicating that the magma was probably derived from partial melting of juvenile crust. The granodiorite has relatively low Mg# values (mean 36.24).
Conclusions Combined with geochemical characteristics and previous studies, the Dawopu adakitic granodiorite in northern Liaoning was most likely formed by partial melting of thickened lower crust, under the background of continuous collision between two major plates after the closure of the Paleo−Asian Ocean.
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