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Original Article |
1 1Key Laboratory of Crustal Deformation and Processes, Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China
2 2Beijing SHRIMP Centre, Chinese Academy of Geological Sciences, Beijing, 100037, China (e-mail: tozhangshuanhong@163.com)
3 3Department of Earth Sciences, Nanjing University, Nanjing 210093, China
4 4Geological Information Centre, Ministry of Land and Resource, Yanjiao, Hebei Province 065201, China
We report four late Palaeozoic zircon sensitive high-resolution ion microprobe (SHRIMP) U–Pb ages for granitic plutons from the Inner Mongolia Palaeo-uplift on the northern margin of the North China block. These cast a new light on the poorly understood tectonic history of the northern margin of the North China block and the Central Asian Orogenic Belt during the late Palaeozoic. The plutons have for a long time been considered to belong to the early Precambrian basement of the North China block. Our new SHRIMP U–Pb zircon dating of four plutons at Longhua, Daguangding, Boluonuo and Hushiha has yielded intrusive ages of 311 ± 2 Ma, 324 ± 6 Ma, 302 ± 4 Ma and 310 ± 5 Ma, respectively. Geochemical data suggest that these granitoids have a calc-alkaline, subduction-related I-type signature, indicating the existence of an Andean-style continental arc along the northern margin of the North China block during the late Palaeozoic. Our results also indicate that the Palaeo-Asian Ocean still existed during latest Carboniferous–earliest Permian time, and that the final collision between the southern Mongolia composite terranes and the North China block occurred later than c. 290 Ma. We suggest that the northern margin of the North China block was an active continental margin and the Inner Mongolia Palaeo-uplift is a deeply exhumed mid-crustal ‘root’ of a late Palaeozoic Andean-style continental arc.
