内蒙赤峰楼子店拆离断层带下盘变形花岗质岩石的时代、成因及其地质意义－锆石U-Pb年龄和Hf同位素证据

Located in the northern margin of the North China Craton, the Louzidian metamorphic core complex is one of the important areas with widely distributed Palaeozoic-Mesozoic granitoid rocks. The deformed plutonic intrusions in the Louzidian core complex area have not yet been precisely constrained by reliable isotopic ages. The plutons have long been considered to be Precambrian rocks. Recent studies have revealed that the deformed and metamorphosed rocks with protolithes of plutonic intrusions were genetically related to late ductile shear events. This paper presents newly obtained zircon U-Pb ages of the deformed granitoids from Zhalanyingzi (253.6±1.2 Ma), Chaoyanggou (150.42±0.98 Ma), Molihaigou (127.6±3.1 Ma) of the Liuzidian metamorphic core complex area in Chifeng, on the northern margin of the North China Plate. Hafnium analyses show that the three deformed granitoids have negative and variable eHf (t) values (-5.1 to-14.9) and Meso-Palaeoproterozoic (1.5 to 2.2 Ga) depleted-mantle model ages, suggesting the probable derivation from an isotopically heterogeneous old crust source. The source region for these magmas might have been related to Meso-Palaeoproterozoic material of the North China Craton underlying Chifeng. Based on zircon U-Pb data, the authors identified four stages of granitic magmatism, i.e., Late Carboniferous (327 Ma), Permian (285~252 Ma), Early Jurassic-Middle Triassic (241~184 Ma) and Early Cretaceous-Middle Jurassic (163~125 Ma). The new ages indicate that these plutons were emplaced in the late Palaeozoic-Mesozoic period. Early Carboniferous granite implies the existence of an Andean-style continental arc along the northern margin of the North China Block. The Permian granitic magmatism was probably related to the extension due to the final closure of the Paleo-Asian Ocean and the amalgamation of the Mongolian arc terrain with the northern North China Block. These events were followed by post-collisional/post-orogenic extension and large-scale magmatism during Triassic. Early Cretaceous-Middle Jurassic (163~125 Ma) magmatism in the Louzidian core complex area was developed in an extensional setting, possibly induced by lithospheric thinning in the North China Block. The geochronological framework provides important information for the constraint of the Paleozoic-Mesozoic tectonic evolution in the northern margin of the North China Block.