Late Mesozoic Structural Deformation And Paleotectonic Stress Field Around Luanping County,North Hebei Province And Changping County,Beijing

It was believed by many wokers that the Mid-Cretaceous is the peak stage of destruction of North China Craton,and structural deformations during which are dominated by extensional structures,such as metamorphic core complexes.However,other researchers have found well developed and widespread extensive contraction deformations in the north of North China Craton during middle of Early-Cretaceous or late of Early-Cretaceous.Because of the localizations of the development of metamorphic core complexes,and the lack of analysis on paleotectonic stress field,the paleotectonic stress field during the peak stage of destruction of North China Craton remains unknown up to now.This paper focus an area around Luanping county,North Hebei Province and Changping county,Beijing in north of North China Craton for paleotectonic stress field study.Most fault slip data were collected from intrusive pluton rocks,especially of Cretaceous.Win-TENSOR program was imployed in this study for paleostress field inversion.Timing sequence of paleostress filed was established based on interrelations between outcrop-scale structures and striae together with regional tectonic deformation history proposed by previous researchers.The isotopic age of data intrusive rocks was incorporated in the definition of paleostress filed history in this region.This study revealed that the paleotectonic stress field evolution and its characteristic in the peak stage of destruction of North China Craton as follows:1.Four generations or five Stages of paleostress fields have been defined since Late-Mesozoic in the area from Luanping county,North Hebei Province to Changping county,Beijing.D₁.From the end of Jurassic to middle of Early-Cretaceous,there are NW-SE compression paleostress field(D_1-1)and N-S compression paleostress field(D_1-2).These two generations may exist synchronously and may last to middle of Early-Cretaceous at least.D₂.A stretch stress field in main direction of NW-SE with a widespread multidirectional extension due to the vertical principal axis of stressσ₁ develops in middle to late of Earl-Cretaceous.（135Ma-100Ma）D₃.A widespread existence of NE-SW weak compression with a few of structures in late of Early-Cretaceous or Late Cretaceous.D₄.An E-W compression may exist in Paleogene.2.Compression paleostress field should last to middle or late Early-Cretaceous.It means in the peak stage of destruction of North China Craton,it still has compression paleostress field superimposed on stretch paleostress field.It should be the feature of paleostress field in the peak stage of destruction of North China Craton.The existence of compression paleostress field during the peak stage of destruction of North China Craton should be considered when constructing models.