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Meta-Sedimentary Rocks and Tectonic Division of the North China Craton

WU Chang-hua   

  1. Tianjin Institute of Geology and Mineral Resources, Tianjin 300170, China
  • Received:2007-09-20 Revised:2007-09-20 Online:2007-09-20 Published:2007-09-20

Abstract: The basement of the North China craton, like many other old cratons in the world, consists mainly of tonalitetrondhjemite-granodiorite gneisses (TTG), greenstone belts and a small amount of Precambrian meta-sedimentary rocks. Although the meta-sedimentary rocks are less distributed, their evolution regularities can be reflected by TTG, because a sedimentation in Precambrian always followed a cycle of granitoid continental crust. According to incomplete statistics of the Precambrian granitoid ages from the North China craton, it is showed that the craton experienced multiple phases of evolution from a nucleus to a mature continent through the cycle events at 3.8 Ga, 3.3 Ga, 2.9 Ga, 2.5 Ga and 1.8-1.9 Ga, which are exhibited by peaks on the histograms of granitoid ages and by ca. 500 Ma as a period. Correspondingly, the amount of sedimentary rocks increased along with evolution of granitic crust, but the deposition was temporally different from the granitoid events, i.e. deposition took place between two cycles of granitoids crust with a period of ca. 500 Ma. This period is similar to the interval in a Phanerozoic supercontinental cycle from breakup to assembly, indicating similar continent evolution regularities in both Precambrian and Phanerozoic. Therefore, it is possible for using meta-sedimentary rocks to interprete the craton evolution. However, the Precambrian (especially the Archean) sedimentary rocks are so minor that they cannot reveal the shape of the old blocks. Meanwhile, the Paleoproterozoic khondalite series was deposited in a continent-marginal setting and is better conserved and distributed, it can be used to model the assembly of craton. Generally speaking the tectonic division based on khondalite should be the best among many other tectonic models for the North China craton, because the marginal sedimentary rock was the boundary of block. Thus, based on khondalite and combined with magmatism, sedimentology, metamorphism, structural deformation, and geochronology in a variety of Archean terranes, a new tectonic subdivision model for North China craton is presented in the paper. The tectonic units are succesively: from west to east, Ordos block / Central (Jin-Meng) assembly belt / Ji-Lu-Yu block / (Tan-Lu fault) / Seashore (Jiao-Liao) block group.Because the protolith ages of the khondalite are Paleaoproterozoic, the final assembly occurred at ~1.8-1.85 Ga, i.e. the famous Lüliang Movement in China .