Geochronology and Geochemistry of the Early Jurassic Granitoids in the Central Lesser Xing’an Range, NE China and Its Tectonic Implications
详细信息
- 责任者：Xu Meijun (College of Earth Sciences ; Jilin University ; Changchun 130061 ; China) ; Xu Wenliang
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(2)
- 关键词：花岗岩 ; granite ; 小兴安岭 ; Xiao Hinggan Mountains
- 页码：p.354-368
- 图表：illus., 3 tables, 49 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
LA-ICP-MS zircon U-Pb dating and geochemical data are reported for three granites and one biotite monzonite in the central Lesser Xing’an Range in order to constrain its formation time, petrogenesis and the regional tectonic setting. Zircons from four representative intrusive rocks are euhedral-subhedral in shape and display oscillatory growth zoning in CL images, implying their magmatic origin. The dating results indicate that the granites and biotite monzonite from the northwestern Lesser Xing’an Range formed in the Early Jurassic (175～185Ma). The granitoids have SiO2=67.32%～75.61%, Al2O3=12.76%～16.71%, Na2O+K2O=8.07%～10.40%, Na2O/K2O=0.94～1.67, A/CNK=0.91～1.06, A/NK=1.09～1.27, and belong chemically to high-potassium calc-alkaline I-type ones. Moreover, these granitoids are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), and depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs). Their zircon εHf(183～185Ma) values range from +6.3 to +10.8, and Hf two-stage model ages vary from 754Ma to 1092Ma, implying that their primary magmas were derived from partial melting of the juvenile lower crust. The Early Jurassic granitoids, together with coeval mafic-ultramafic intrusive rocks in the Lesser Xing’an-Zhangguangcai Range, constitute a typical bimodal igneous rock association, suggesting an extensional environment. Combined with the spatial compositional variation of the Early Jurassic igneous rocks in NE China, it is suggested that the Early Jurassic granitoids from the Lesser Xing’an Range formed under an extensional environment similar to back-arc basin which could be related to double-subductions of the Paleo-Pacific plate beneath the Eurasian continent and the Mongol-Okhotsk oceanic plate beneath the Erguna Massif.