Tectonic evolution of the northeastern North China Craton: Constraints from geochronology and Sr–Nd–Hf–O isotopic data from Late Triassic intrusive rocks on Liaodong Peninsula, NE China

Abstract

This paper reports new whole-rock major and trace element, SrNd isotopic, and zircon UPb and HfO isotopic data for Late Triassic intrusive rocks on Liaodong Peninsula, NE China, aiming to constrain the petrogenesis of these rocks in terms of lithospheric thinning in the northeastern North China Craton (NCC). New zircon UPb data indicate that the rocks were emplaced during the Late Triassic (220–211 Ma). Based on petrology, petrography and geochemistry, we divided these rocks into three groups. The Group 1 rocks, including hornblende gabbro, hornblende diorite and mafic vein, show low SiO2, Na2O + K2O and high MgO contents, with (87Sr/86Sr)i (0.7066–0.7071), εNd(t) (−10.6 to −5.7), εHf(t) (−16.6 to +1.5), and δ18O (7.06‰–7.82‰) values, indicating that they were formed by partial melting of lithospheric mantle with addition of lower continent crust materials. The Group 2 rocks, including syenites, display high SiO2, Na2O + K2O and low MgO contents, with (87Sr/86Sr)i (0.7064–0.7073), εNd(t) (−14.8 to −14.5), εHf(t) (−11.7 to −5.7), and δ18O (5.49‰–6.37‰) values, indicating they were originated through partial melting of lithospheric mantle with continent crust materials added, coupled by fractional crystallization of mafic minerals. The Group 3 rocks, including monzogranite and syenogranite, show high SiO2, Na2O + K2O and low MgO contents, with different isotopic signatures: the former shows (87Sr/86Sr)i (0.7085–0.7087), εNd(t) (−17.0 to −16.8), εHf(t) (−17.9 to −4.4) and δ18O (6.10‰–6.95‰) values. The latter shows higher εNd(t) (−9.0 to −8.1), εHf(t) (−3.4 to +1.2) and lower δ18O (5.52‰–7.29‰) values. Combined with the adakitic features of monzogranite and different two model ages, we believe they were derived from partial melting of ancient thickened lower crust and juvenile crust, respectively. Together with the spatial and temporal distribution of the Late Triassic rocks, we believe that these rocks were related to the collision between NCC and Yangtze Craton, and the initiation of lithospheric thinning of NCC in eastern segment began in Late Triassic.