The Initiation, Evolution And Abandonment Of The Jianghan Basin:Combined Influence Of Basement Structures And Mantle Dynamics

Intracontinental rift basin is the embryo of the Wilson cycle and the important component of continental rifting and the subsequent opening of oceans.However,the formation mechanism and dynamics of intracontinental rift basin remain poorly understood or different ideas often conflict with each other.The uncertainty is generally caused by using single-disciplinary approach and/or studying rifting and volcanism separately.Most previous studies only focused on a certain period?mainly the late Cenozoic?rather than the whole rifting process.Importantly,when intracontinental rift basins are widely distributed with off-rift volcanism,whether the underlying driving mechanism can be explained through classic plate tectonic and mantle plume theory remains hotly debated.The widespread rifting and magmatism in eastern China have attracted the world's attention.This study focuses on the Jianghan Basin in eastern China and tries to unravel the temporal and spatial variations of rifting and volcanism based on the extensive 2-D and 3-D seismic data,borehole data,field data and basalt geochemical data,aiming to illustrating the characteristics and constraints on the initiation,evolution and abandonment of the Jianghan Basin.The Jianghan Basin evolved on a crystalline basement covered by thick pre-rift strata.Basement structures have crucial influence on the rift geometry of the Jianghan Basin?including its location,shape and architecture?.Pre-rift basement strata near the fault planes in the hanging walls of the major rift-related faults are older than these in the footwalls and for most faults pre-rift strata in the hanging walls become progressively older as proximity to the fault planes increases,suggesting that these faults have reactivated pre-existing thrusts or thrusts associated with unroofed folds through negative structural inversion.The major rift-related faults in the Jianghan basin have very high D_max/L ratios?0.11-0.66?than the typical normal faults,likely resulting from either constant length fault model or low frictional strength.Therefore,rift-related faults preferentially initiate on the pre-existing thrust faults rather than initiating independently.The unique spatial geometry of the Jianghan Basin is controlled by its multidirectional basement structures.Basement structures also play an important role in rift localization.Generally,there is a positive correlation relationship between basement deformation strength and the thickness of rift sequences.The weakest central interfering and converging zone localized the maximum depocentres and rifting progressively focused in it as rifting proceeded,while the region out of the interfering and converging zone progressively failed.The multidirectional basement reactivation and extension with rift localization inspire our understanding of triple junctions.The Early Cretaceous?146-100 Ma?strata were deposited within a series of localized depressions distributed on the basin margin while they were absent in the most region of the basin.Subsequently,the Jianghan Basin underwent three-phase rifting and volcanism during the the Late Cretaceous to Cenozoic.During the Late Cretaceous?100-65 Ma?,widespread rifting and sporadic volcanism initiated in the Jianghan Basin,with a distributed distribution.During the Cenozoic,both rifting and volcanism initiated/initially focused in the western basins and then progressively migrated eastward together with the depocentres?regardless of the Cenozoic migration of volcanism in the Jianghan Basin?,rather than directly continuing migrating eastward.Rifting and volcanism during the middle Cenozoic?50-23 Ma?were significantly enhanced and all the rift basins in eastern China failed at ca.26 Ma.All the Jianghan basalts were derived from the partial melting of asthenospheric mantle.The asthenospheric mantle sources beneath the studied basins got isotopically more depleted with an increasing melting extent from the Late Cretaceous to early Cenozoic?65-50 Ma?,while it got isotopically more enriched and heterogenous with a decreasing melting extent?significantly reduced volatile content?from the early Cenozoic to middle Cenozoic.During the Cretaceous,the rollback of the Pacific slab triggered the widespread rifting and magmatism in eastern China.However,the lithosphere beneath eastern China were too thick to rift,merely getting rapidly thinned under the influence of the asthenospheric upwelling.Meanwhile,the upwelling asthenosphere and intruded dykes/magma heated and weakened the lithosphere,leading to thermal doming of the most region of the Jianghan Basin.Only a set of localized depression sequences were deposited on the basin margin.Through the Early Cretaceous proto-rift evolution,the lithosphere was thin enough to rift during the Late Cretaceous.Under the diapirism of the continuously upwelling asthenospheric mantle,widespread rifting initiated in the Jianghan basin,reactivating the multidirectional basement structures.With the tectonic correlations between the Jianghan Basin,eastern China and adjacent plates and geochemical constraints,our observations on the Cenozoic rifting and volcanism consistently coincide with India-Asia collision and are in conflict with the rollback of the Pacific slab.Thus,although the Cretaceous tectonic evolution of the Jianghan Basin and eastern China was associated with the rollback of the Pacific slab,the Cenozoic intracontinental rifting and volcanism in the Jianghan Basin and eastern China have been driven by India-Asia collision during the Cenozoic.However,the Cretaceous tectonic evolution of eastern China has a crucial influence on the following Cenozoic tectonic evolution.Through the Cretaceous tectonic evolution,the lithosphere and asthenospheric mantle beneath eastern China has been characterized by different characters between the east and west sides of the North-South Gravity Lineament?NSGL?.When the collision-induced multistage asthenospheric flow easterly passed through the NSGL,a series of physical and chemical changes occurred,causing the shallow responses?temporal and spatial variations of rifting and volcanism?in the Jianghan Basin and eastern China.This study verifies the asthenospheric flow model through a multidisciplinary approach,supplementing and enriching the classic plate tectonic and mantle plume theory from a new perspective.Furthermore,this study unravels the completed development processes of the Jianghan Basin?from initiation to abandonment?,and proposes the combined constraint model of“multistage control of basement structures,multiphase drive of mantle”,providing an answer to how and why the Jianghan Basin initiated,evolved and subsequently failed.Therefore,this study will be of great referential significance to the studies on the formation mechanism and dynamics of intracontinental rifting and volcanism globally.