Late Paleoproterozoic crustal evolution in the Daqingshan area: Evidences from adakitic and A-type granitoids in the Guyang Changshengqu goldfield, Khondalite Belt, North China Craton

摘要

Granitic magmatism related to the collisional orogenic belt provides important information for the evolution of continental crust. We performed petrological, geochemical and zircon U-Pb-Hf isotopic studies on four granitoid samples from the Guyang Changshengqu goldfield, Daqingshan area, Khondalite Belt, North China Craton. The zircon U-Pb dating results indicate that the granitoids emplaced at 1950 +/- 11 Ma, 1935 +/- 12 Ma, 1846 +/- 11 Ma, and 1812 +/- 8.6 Ma, represent two periodic granitic magmatism in the Daqingshan area. The 1.95 and 1.93 Ga granites exhibit high SiO2, K2O, and Na2O contents with high Sr/Y and (La/Yb)(N) ratios, but low MgO, Cr, and Ni contents, indicating that they were produced by the partial melting of a thickened lower crust under relatively high-pressure conditions. The granites show negative-dominated zircon epsilon(Hf)(t) values (-5.7 to 1.9), and their zircon T-DM2(Hf) values range between 2.9 and 2.5 Ga, indicating an ancient crust source with minor juvenile crustal material involved. The 1.85 and 1.81 Ga quartz monzonites exhibit high SiO2, K2O, Na2O, Zr, Nb, Ce, and Y but low MgO, Cr, and Ni contents, with high Ga/Al and FeOt/(FeOt + MgO) ratios, indicating an A-type granite affinity. The whole-rock geochemistry suggests that they were formed by dehydration remelting of TTG and quartz diorite at high temperatures and shallow depths. The quartz monzonites show homogeneous epsilon(Hf)(t) values (-10.6 to -6.1) and the zircon T-DM2(Hf) values range between 3.0 and 2.8 Ga, suggesting that they were derived from a Neoarchean ancient crust. The 1.95-1.93 Ga adakitic magmatism is associated with the 1.93-1.92 Ga mafic magmatism and UHT metamorphic in the eastern part of the Khondalite Be this suggests a tectonic transition from collisional compression to post-collisional extension. The 1.85-1.81 Ga A-type granitic magmatism indicates evident continental crust thinning and asthenospheric upwelling. The two unrelated magmatism are possibly induced by two collisional events from the Khondalite Belt and the Trans-North China Orogen, respectively. The collision of the western and eastern blocks at ca. 1.85 Ga may have played an important role in the A-type quartz monzonites origin and influenced the crustal evolution as far as the Daqingshan area in the Khondalite Belt.