Tectonic Evolution And Significance Of The Central Part Of The Trans-North China Orogen During The Late Paleoproterozoic

The North China Craton is one of the oldest cratons in the world,recording almost all major geological events in the evolution history of the Earth.Previous studies have shown that the Paleoproterozoic is a key period for the tectonic evolution of the North China Craton,mainly involving the formation of the unified North China Craton,and the transition from the vertical accretion of the continental crust to the modern plate tectonic regime in North China,and possibly related to the Major events in the tectonic evolution of Colombia supercontinent.However,the previous research about the tectonic evolution of the North China Craton during Paleoproterozoic were mainly based on studies of petrology,geochemistry and isotope chronology.The Paleoproterozoic tectonic framework,deformation characteristics and tectonic processes are still unclear in the North China Craton.The Trans-North China Orogen is one of the key point of the debate on the tectonic evolution of the North China Craton in recent years.The predecessors proposed a variety of tectonic evolution models,which mainly can be divided into two different understandings,one propose it is formed by the collision of ~1.85 Ga between the Eastern block and Western block of the North China Craton,which led to the unification of the North China Craton,the other propose that it is a activity belt formed in the Paleoproterozoic extension and cleavage events,and the unified North China Craton has formed at the end of the Archean(~2.5 Ga),the debate between them is concentrate on the tectonic property of the Trans-North China Orogen.There are a series of large ductile shear zones in the central part of the Trans-North China Orogen,which divide the area into several important metamorphic complex blocks.The authors carried out detailed research on the geometric,kinematic,microstructure and geochronology characteristics of these ductile shear zones,.and results indicate that the nearly EW-trending Zhujiafang ductile shear zone shows the sinistral shearing,and the NEE-trending Wangjiahui ductile shear zone shows the dextralt shearing,and the NE-trending Longquanguan ductile shear zone is a low-angle shear zone with top-to-NW extending shearing it is basically determined that the time of these shear zones is the late Paleoproterozoic(1.85~1.78 Ga).According to these shear zones,we re-divide the tectonic units of the Hengshan-Wutai-Fuping area in the Trans-North China Orogen and several Precambrian metamorphic blocks are defined,including the Hengshan block,the Fanshi block(south Hengshan complex and the northern part of the Wutai complex divided by the predecessors),the Wutai block and the Fuping block,and differentblocks have undergone different metamorphism and tectonic evolution history.The kinematic orientation of the ductile shear zones between these blocks reveal the mutual motion relationship between them in the late Paleoproterozoic,which show the complex tectonic process in the central part of the Trans-North China Orogen.Three important tectonic deformation events occurred in the central part of the Trans-North China Orogen in the late Paleoproterozoic:(1)The indentation of the Fanshi block from SW to NE,which concludes that the Fanshi block may be from the basement of the Ordos block in the west,or the from the Lüliang block in the southwest,the Wutai block deformed and backward in the southeast direction during the process of extrusion of the Fanshi block(D1);(2)The uplifting of the Fuping block and large-scale extension,which caused the Fuping complex uplifted to the near-surface and formed the low-angle ductile shear zone with top-to-NW extension between the Fuping and Wutai block(D2).indicate that the large-scale extension event inthe North China Craton might begin at the late Paleoproterozoic;(3)A large number of NW-NNW trending mafic dyke swarms caused by NE-SW stretching(D3).After those tectonic events,the Xiong'er rift in the southern margin and the Yanliao rift in the northern margin of the North China Craton began to develop,which represent that the craton entered a relatively stable evolutionary stage.Therefore,the tectonic framework of the central part of the Trans-North China Orogen(or even the North China Craton)is probably represent by the Precambrian blocks separated by several boundary ductile shear zones.Tectonic events between Precambrian blocks may represent typical deformation style of the Trans-North China Orogen in the late Paleoproterozoic.The indention tectonics of Fanshi Block may correspond to the background of the collision and assembly of the Eastern Block and Western Block in North China,and might be correlated to the amalgamation of the Columbia supercontinent The large-scale extensional ductile shear zone may indicate that t the extensional tectonic setting of the North China Craton in late Paleoproterozioc,and may also be correlated to the break-up of Colombia supercontinent.