The Research On The Genesis And Mechanism Of The Shanxi Rift System,with A Focus On The Datong Basin

The origin and mechanisms underlying intracontinental rifts have long been a central focus of structural geology research,especially in the context of Cenozoic intracontinental rifts.These rifts,due to their extensional tectonics,often trigger seismic and volcanic activities,with significant implications for human safety.The Shanxi Rift System stands as one of the most well-preserved intracontinental rift systems in Asia,yet debates persist regarding its formation timing,evolutionary processes,and controlled geodynamic mechanisms.While the North China Craton has remained tectonically stable since the late Precambrian,the Shanxi region within its core has experienced rifting during the Cenozoic,shaping the present-day basin-mountain topography.However,the genesis mechanisms of the Shanxi Rift System remain highly contentious.Therefore,the investigation of the Shanxi Rift System’s genesis not only contributes to a deeper understanding of intracontinental rift mechanisms but also provides a theoretical basis for geological hazard prediction.This paper employs an integrated approach,combining methods such as magnetotelluric surveys,apatite fission track analysis,and numerical simulations.Through the analysis of both deep-seated and shallow-seated structural features,we explore the spatiotemporal relationships between deep mantle and shallow crustal structural forms.This approach sheds light on the formation processes,genesis mechanisms,and structural evolution of the Shanxi Rift System in the central North China Craton.Analysis of geological characteristics from magnetotelluric surveys in the Datong Basin of the Shanxi Rift System reveals that normal and strike-slip faults jointly control the subsidence and sedimentation within the basin.The cumulative fault displacement within Cenozoic strata reaches approximately 1500 meters,with displacements of around1000 meters observed within the Neogene strata.This suggests that the basin experienced a phase of weak extension during the Paleogene and a subsequent phase of intense extension during the Neogene.Magnetotelluric profiles unveil the presence of deep-seated magma conduits beneath the Datong Basin.Upwelling mantle flow from the asthenosphere results in crustal extension,leading to the formation of rift basins,crustal magma chambers,surface geothermal resources,and Cenozoic basaltic volcanism in the region.This study,combined with previously published low-temperature thermochronological data,reveals a south-to-north decreasing exhumation rate within the Shanxi Rift System during the Eocene to Oligocene(50～30 Ma),followed by a phase of intensified exhumation across the entire region since the early Miocene(20 Ma).Integrating thermal history simulations and tectonic evolution,this study propose that the initial rifting of the Shanxi Rift System occurred during the Eocene to Oligocene(50～30Ma)and matured since the early Miocene(20 Ma),supporting the hypothesis of a south-to-north rift propagation.Utilizing finite element modeling with inputs of crustal motion rates derived from GPS observations and constraints on mantle flow rates,the simulations show that when crustal motions exhibit opposite directions(5 mm/yr to the left and 2 mm/yr to the right),the resulting surface sedimentary patterns,lithosphere-asthenosphere structural forms,and geological-geophysical interpretations closely match those of the Datong Basin.This model reveals key features of mantle convection,where horizontal convergence of mantle flow on both sides of the Shanxi Rift System induces mantle upwelling.This upwelling creates lithospheric-scale rift structures and triggers backward motion of the crust,leading to sustained sedimentation along two sedimentary centers.Geodynamic analysis indicates that during the Paleogene,the Shanxi Rift System underwent extension related to the northwest-southeast subduction of the Pacific Plate.This extension resulted in northeast-southwest-trending normal faults and the development of NE-trending rift basins.Since the Miocene,the Shanxi Rift System has been influenced by the collision between the Indian Plate and the Eurasian Plate,along with the subduction of the Pacific Plate.This has led to the development of thick Cenozoic to Quaternary sedimentary sequences along NE-trending normal faults.The magnetotelluric profiles in the Datong Basin,numerical modeling,and tectonic history collectively support the concept of an upwelling mantle flow-induced rift.This mantle flow results from the dehydration of the forearc mantle wedge due to the subduction of the Pacific Plate and the extrusion of mantle flow from the northeastern margin of the Tibetan Plateau.The upwelling mantle flow erodes the crust and thins it,while mantle flow escapes laterally beneath the lithosphere.The extensional stresses generated by this process ultimately lead to crustal rifting and the formation of the Shanxi Rift System.