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Provenance analysis of the conglomerate clastic compositions from the Late Jurassic Chengde basin and its tectonic significance

2007; Science Press; Linguagem: Inglês

2095-8927

He Zheng,

Geological formations and processes

A mass of coarse clastics were accumulated in the Chengde and Shouwangfen Basins of Hebei Province during the Late Jurassic.Clasts of conglomerates from the Late Jurassic Tuchengzi Formation have been categorized as three assemblages in the Chengde and Shouwangfen basins,which include crystalline basement and volcanic rocks,carbonates and volcanic rocks,and volcanic rocks and carbonates.The crystalline basement and volcanic rocks are predominant in coarse clastics among the three assemblages, indicating that the part of theInner Mongolia Axison the north of the Chengde basin was the main provenance throughout the Late Jurassic.Conglomerate clastie compositions on the both sides of the Shuangmiao fault,thrusting northward and cutting the Cbengde basin to two parts,are basically consistent.It reflects that clastic compositions on the both sides of the thrust fault together derived from the north provenance.This evidence implies that the fault was weakly active in the most of the Tucbengzi time (probably intensive activity in post-Tuchengzi time?).Our analysis shows that conglomerate elastic composition on both the limbs of the asymmetrical syncline in the south of the Chengde basin is completely different,which reflects the clastic distribution was controlled by the syncline as a syn-depositional structure.Clastic supplies (dolomites and volcanic rocks) from the south of the basin were markedly less than those of the north,revealing that the Huiyao thrust fault was a secondary order fault,which controlled the development of the south limb of the Chengde syncline.The both faults,the Huiyao and Shuangmiao faults,as back-thrust faults, probably played a role of accommodation fault due to propagation of main thrust system southward-directed in the Tuchengzi time.According to coupling between basin filling and contemporary thrust belt,accumulations of a mass of coarse clasties from thrust front possibly implies that existed strong thrusting on the north of the Chengde basin during the Late Jurassic.The results of this study suggest that the northernInner Mongolia Axisas the main provenance suffered intense uplift-erosion process.We presume that once the provenance on the north of the Yanshan thrust belt was topographically possible an east-west directed paleo-mountain range (or paleo-plateau?) in that time.