The geological architecture and the deformation process of the southern and northern limbs of the Zigui synclinorium in Sichuan Basin were studied by analyzing data of the shallow layers and the newest deep seismic data

with a view to discuss the way of superimposition of the deformation fronts of the Dabashan structural zone with the West Hunan and Hubei fold zone.The study indicates that the activity of deep tectonic wedges is the main driving force for the deformation of the southern and northern limbs of the Zigui synclinorium.The tectonic wedge under the southern limb takes the south-dipping fault plane connecting the Silurian decollement layer with the basement decollement layer as the floor front-thrust fault

and takes the Silurian decollement layer and the north-dipping fault plane above it as the roof back-thrust fault

and the tectonic wedge composed of strata from the Silurian shales to the top of the Sinian as well as part of the deep basement material gets involved in deformation.The tectonic wedge under the nor-thern limb takes the basal decollement layer in the northern limb of the syncline as the roof back-thrust fault

takes the decollement layer in the deep as the floor front-thrust fault

and the tectonic wedge is consisted of basement materials as a whole.Further analysis shows that the formation of the southern limb of the Zigui synclinorium is controlled by the progressive deformation of the West Hunan and Hubei fold belt from the Late Jurassic to the earliest of the Early Jurassic

and the northern limb

as well as its inner secondary folds

is formed as a result of the southward compressive nappe of the South Dabashan thrust belt within the Dabashan structural belt from the middle to the late of Early Cretaceous.The overprint of the middle Early Cretaceous-Late Cretaceous deformation of the Dabashan structure on the Late Jurassic deformation of the West Hunan and Hubei fold belt is the basic pattern for the superposition deformation of the two structural belts.