兴凯地块南部花岗岩年代学、地球化学及Hf同位素特征

Abstract

The tectonic evolution of southern Khanka block is very complex,and there is not enough of the precise chronological evidence and systematic geochemical studies.Zircon U-Pb dating results show that the granites from southern Xingkai block were intruded at the end of Late Triassic (202-205 Ma)in a transition stage of paleo-Asian Ocean and paleo-Pacific tectonic system.It is found that the monzonitic granites and granodiorites are all characterized with enriched silicon (SiO2 =69.61%-77.27%),weakly supersaturated aluminum (Al2 O3 =12.70%-15.28%)and relatively enriched potassium (AKI=0.64-0.88),which indicates that the granites are fractionated I-type granites,taking into account of the presence of amphibole and low zircon saturation temperature (TZr=679-787 ℃).176 Hf/177 Hf ratios are high (0.282 773-0.282 913);eHf (t)is positive (4.39-9.32),and two-stage Hf model ages are young (0.65-0.96 Ga),which shows that its source material is from the depleted mantle of new-born young crust of Neoproterozoic.It is concluded that the granite was formed in the context of the initial western Pacific subduction into active continental margin based on the age of the rock formation,and other rock features.