辽东半岛中生代花岗质岩浆作用的年代学格架

Geochronological Framework of the Mesozoic Granitic Magmatism in the Liaodong Peninsula, Northeast China

辽东半岛是我国东部中生代花岗质岩石较为发育的地区.传统观点认为,该区花岗岩以三叠-早中侏罗世(印支-早燕山期)为主.采用SHRIMP、TIMS和LA-ICPMS三种方法,对60 余个样品中的锆石进行了U-Pb同位素年代学测定.根据这些资料,目前可以将该区中生代花岗质岩浆作用划分为3个阶段:三叠纪 (233～212 Ma)、侏罗纪 (180～156 Ma) 和早白垩世 (131～117 Ma).与以前认识不同的是,区内的花岗质岩石以早白垩世为主.对比华北地台其它地区中生代岩浆作用的年代学格架发现,三叠纪-侏罗纪花岗岩主要出现在华北东部,而早白垩世花岗岩在全区均较发育,这一分布特征为探讨华北中生代地质演化提供了重要信息.

Liaodong Peninsula, located in the northeastern part of the North China Craton （NCC）, is one of the important areas where the Mesozoic granitoid rocks are widely distributed. It is traditionally thought that the granitoids in this area were mainly emplaced during Triassic to early-middle Jurassic. In this paper, more than 60 samples of zircons have been run for U-Pb geochronological dating using SHRIMP, TIMS and LA-ICPMS techniques. Based on these new data, three stages of granitic magmatism are identified： Triassic （233 -212 Ma）, Jurassic （180- 156 Ma） and Early Cretaceous （131 - 117 Ma）. The Triassic plutons include alkaline syenite （Saima- Bolinchuan）, dolerite, diorite and monzogranite. The Jurassic granites are characterized by ductile deformation and a lot of inherited zircons. Some plutons of this stage were considered as Archean tonalite and Proterozoic intrusions or migmatites. The Early Cretaceous intrusions are consisted of numerous rock types, including dolerite, diorite, monzonite, porphyritic granite, highly fractionated alkali feldspar granite and A-type granite, and occurred usually as large batholiths. Magma mixing is extensively developed between the diorite and granite. The major difference from the previous thought after throughout geochronological analyses is that the early Cretaceous is the most important period of granitic magmatism in this area. Comprehensive comparisons with granitoids in other areas of the NCC, it is found that the Triassic-Jurassic granitoids are mostly exposed in the eastern part of the NCC, whereas the Early Cretaceous granitoids are developed in all areas. This geochronological framework provides important informa- tion to constrain the Mesozoic tectonic evolution of the NCC.