兴凯地块南部花岗岩年代学、地球化学及Hf同位素特征

兴凯地块南部构造演化复杂，缺乏精确的年代学证据和系统的地球化学研究.锆石U-Pb年龄测定结果表明:兴凯地块南部花岗岩侵位结晶年龄为晚三叠世末期(202~205 Ma)，处于古亚洲洋和古太平洋构造体制的转换阶段.地球化学成分上，二长花岗岩和花岗闪长岩均以富硅(SiO₂=69.61%~77.27%)、弱过铝(Al₂O₃=12.70%~15.28%)、较富碱(AKI=0.64~0.88)为特征.结合角闪石矿物的出现、较低的锆石饱和温度(T_Zr=679~787 ℃)等特征表明本区花岗岩为分异的Ⅰ型花岗岩.锆石的176Hf/177Hf比值较高(0.282 773~0.282 913)，ε_Hf(t)均为正值(4.39~9.32)，二阶段Hf模式年龄较为年轻(0.65~0.96 Ga)，反映其源区物质为新元古代期间从亏损地幔新增生的年轻地壳物质.结合岩石形成年龄、岩石组合等特征可以推断岩石应该形成于西太平洋开始俯冲的活动大陆边缘环境下. 

Chronology,Geochemistry and Hf Isotope of Granite from Southern Xingkai Block

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 (Al₂O₃=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 (T_Zr=679-787 ℃). 176Hf/177Hf ratios are high (0.282 773-0.282 913); ε_Hf(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.