The Druse Crystal Calcite Related To Paleo-earthquake Activity In The Jianshan Formation Of The Bayan Obo Group

Meso-Neoproterozoic Bayan Obo rift placed along the northern margin of the North China Craton,which is associated with the cracking of Columbian supercontinent and records this process.During the rift evolution,Syn-sedimentary deformation triggered by tectonic activity,in particular earthquake.Seismic events interpreted in Jianshan Formation,the Bayan Obo Group by typical soft-sediment deformation structures found in siziwangqi area which is in the central segment of the Bayan Obo rift,the druse crystal calcites and collapse developed in Jianshan Formation,which probably provide evolution information of rift.So the evolution of Bayan Obo rift can be better understood at Jianshan Formation.The druse crystal calcites is idiomorphic columnar and accompanied with graphite minerals,pyrite minerals and quartz minerals among crystals.The values of?¹³C from graphite minerals is-20‰indicating biogenic deoxygenation,formed in water.The druse crystal calcite belong to inorganic and grown in hot water environment with 55?according to the values of?¹³C and?¹⁸O from calcites minerals.The calcites grown in paleocave built with fault breccia and the heat sourced from the faulting,the normal fault scrap collapsed and accumulated by earthquake,so the druse crystal calcites can be used as an important evidence to identify seismic events.Collapse included collapsed breccia?fault breccia?and sliding bodies,sliding from NE to SW,differed from Paleocurrent direction of Jianshan Formation.The thickness of collapse was ca.200m,which represented the height of the fault scarp.The strike of the fault scarp was NE-SW by the distribution of collapses.So seismic event in the Jianshan Formation implied that the Bayan Obo rift gone through extended rapidly during the cracking of Columbia supercontinent ca.1.6 Ga.