The Mesozoic-Cenozoic Fault Structure Characteristic And Genesis Mechanism In The Northern Shanxi

Kouquan fault zone,the Northern Liulengshan fault zone and the Northern Hengshan fault zone in the northern Shanxi Province is located on the periphery of the Cenozoic Datong Basin and controls the formation and evolution of the basin.This paper attempts to elucidate the tectonic deformation characteristics and tectonic evolution process of these boundary fault belts through field geological surveys,balanced crosssection recovery,low temperature chronology tests,and discrete elemental particle flow simulations.Based on above researches,discussion on the origin mechanism in combination with regional tectonic settings is conducted.The results show that the compressional stress field of the fault zone in the research area was NW-SE direction in the Mesozoic.Due to differences in pre-existing geological conditions and location distribution,the stress state was not uniform.Kouquan fault zone mainly thrusted westwards,while the Northern Liulengshan fault zone mainly thrusted eastwards and the Northern Hengshan fault zone mainly thrusted southwards.In Cenozoic,under the extensional stress field and accompanied by tectono-magmatic activities(eg.volcanic eruptions),all the regional faults reversed to right-lateral slip normal faults creating rifts inwards,during which time the Datong Basin formed.The fault zones in the research area experienced four tectonic stages from the Mesozoic to the Cenozoic.I.At the end of the Datong period in the middle Jurassic epoch(around 170.2 Ma),the Izanagi plate initiated to subducted underneath the East Asia plate and it entered the first episode of Yanshanian ogogeny.The basement is involved in the transpressional deformation under a compressional stress field in the stratum,which created a preliminary condition for the formation of the fault zones.II.During the late Jurassic epoch and early Cretaceous epoch(149.2Ma~13.6Ma),several fault zones in the research area gradually formed westwards in the late Jurassic epoch.Then it entered the third episode of Yanshanian ogogeny.The regional tectonic stress field changed to extensional,and the fault zones began to rift.III.During the late Cretaceous epoch-Paleogene(86.2Ma ~ 33.4Ma),it entered the fourth episode of Yanshanian ogogeny.The tectonic stress field reversed to compressional due to the continuous subduction of the Izanagi plate.The fault zone responded sorely by overthrusting in the pre-existing weak zones.In Paleogene,the volcanic eruptions occurred due to mantle activities and asthenosphere uplift,forming basalt on the surface of the earth(Fanzhizu basalt).IV.In Neogene,the stress field kept extensional state.Under the influence of volcanic eruptions and other tectono-magmatic activities,the basement experienced transtensional deformation.