四川盆地秭归复向斜构造变形机制及构造意义

为剖析大巴山构造带变形前缘与湘鄂西褶皱带变形前缘的叠加复合方式，通过分析秭归复向斜的浅部资料和深部最新的地震剖面，对秭归复向斜南、北两侧的地质结构和变形过程进行了分析。研究表明：深部构造楔的活动是促使秭归复向斜南、北两翼发生构造变形的主要原因，秭归复向斜南翼构造楔以连接志留系滑脱层和基底滑脱层的南倾断面为底板前冲断裂，以志留系滑脱层及其上部的北倾断面为顶板反冲断裂，由志留系页岩层至震旦系顶部及其深部的一部分基底物质组成构造楔参与变形；向斜北翼深部的构造楔，以向斜北翼基底滑脱层为顶板反冲断裂，以北翼下方深部滑脱层为底板前冲断裂，构造楔整体由基底物质组成。进一步的分析认为：秭归复向斜南翼的形成受控于湘鄂西褶皱带晚侏罗世至早白垩世初向北的递进构造变形，北翼及其内部次级褶皱的形成受控于早白垩世中期至早白垩世晚期大巴山构造带内南大巴冲断带向南的挤压推覆；大巴山构造带早白垩世中期至晚白垩世的变形叠置于湘鄂西褶皱带晚侏罗世的变形之上是两构造带叠加变形的基本模式。

Structural deformation mechanism and significance of the Zigui synclinorium,Sichuan Basin

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.