Mesozoic-Cenozoic Fault Structure Research In Mohe Basin

Mohe basin is located in the northern margin of EerguNa block.The evolution of the basin is under the influences of the Mongolia Okhotsk ocean closure and subduction of Izanagi.This article is based on field geological investigation study,U-Pb isotope dating,ESR dating,geochemical test,geophysical data,fission track thermal simulation and geophysical sections.Meso-Cenozoic characteristic of fault structure was studied in detail.The following results and conclusion have been achieved.(1)The thrusting tectonics is composed of a series of the scale size is different and nearly parallel thrust like plough shape in across section,profile performance for the plow-thrusts posed by the single-chong imbricated structures.According to lithology,metamorphism and deformation characteristics of different nappe can be divided into root zone,middle zone and forward zone.According to the same structure from the root zone of quartz veins and the root zone with the same structure of granite veins date reflecting the overthrust structure is formed in the late Jurassic-early Cretaceous.By analysis with granite vein structure geochemical characteristics,the outcome indicating molten pressure is greater than 1.5 GPa and not less than 50km depth.At the late Jurassic-early Cretaceous the Mongolia-Okhotsk suture was form.It leads to crustal shortening and forms Adakite and Himalayan-type granites.(2)At Early Cretaceous-Cenozoic,Mohe basin is influnced by the ancient Pacific plate subduction.Expansion of the role in this region arc formed tensile stress environment in the research area.Crustal rifting resulted in making the magma upwelling,resulting lithosphere thickened in a background of regional extension rift.The formation of a north-east and north-south faults come into control the volcanic faulted basin.(3)The TianYouershan-MaDaerhe faults belt,BeiJi village-Mohe faults belt and Lonhe-ChangYin faults belt are fromed in the western margin of the basin at early Cenozoic.The faults are characterized by NS strike,steeply dipping high-angle and shallow cut.The early fromed north-south trending faults and north-east trending fault activated at Cenozoic.It may indicate the formation of the new generation in different directions at different times of reactivity.(4)Distributed in the western Mohe basin 12 intermediate-felsic rocks were simulated by fission track.The simulation results show that the basin was experienced uplift and erosion at early Cretaceous and Miocene.Based on comprehensive analysis of existing materials,we divided Mohe Mesozoic tectonic deformation into three stages:(1)from the Jurassic to the beginning of the Cretaceous following the closure of the Kanggai-Kente ocean and subduction of Paleo-Pacific oceanic plate under the Eurasia.The formation of the Mohe County thrust nappe structure which is related to evolution of the Mongolia Okhotsk orogenic belt and NS trending faults.(2)In the Cretaceous extension and thinning of the lithosphere and magmatic activities due to subduct ion of Paleo-Pacific oceanic plate under the Eurasia;(3)crustal disintegration and rifting associated with the subduction of the Pacific plate under the Eurasia since the Eocene.