Late Jurassic Basin Filling Characteristics And Its Marginal Structure Control In Northwestern Hebei Province

The North China craton destruction is one of research focuses in geological community today.But,it has not yet formed a unified view for interpretting the North China craton destruction process and the dynamic mechanism.The processing of basin filling and evolution,as the window to revealed shallow tectonic process of craton, is of great significance for the study of the process of destruction of the North China Craton.In this paper, late Jurassic basins-fill feature and basin margin structures of Chicheng- Xuanhua area in the northern part of the North China Cratonare are analyzed,and thus reveal the nature of the sedimentary basin and basin tectonic setting.The combined study of basin sedimentary stratas and basin margin structure indicate that :During Tiaojishan period,the late jurassic volcanic — sedimentary basins,which formed in compressional tectonic background,were mainly composed of pyroclastic rocks in the beginning, and the volcanic lava overflowing from volcanic activities constituted the end of cycle.The upper,middle and lower sedimentary facies of Tuchengzi formation are respectively alluvial fan deposits, braided river and lake sediments.And,Tuchengzi formation conformately overlies Tiaojishan formation.The systermatically statistical analysis of conglomerate component in Tuchengzi formation shows sthat,Chicheng basin and Xuanhu—Xiahuayuan basin have similar exhumation pattern and lithology phase cycles,witch reveals the source region of two basins had experienced the same or similar erosion process. The thrust faults-associated growth strata can be seen in Tuchengzi formation near the Liqouquan village in the southern Xuanhua county.The thrust faults in Xuanhua—Xiahuayuan—Huailai aera were orth- or northwest-directed thrusts and accompanied by sinistral strike-slip,which characterized by a front-expanding development. And,stratigraphic crosscutting relationship indicates that the time of the thrust faults’ initial movement were after the middle jurassic.Integratting the study of previous and this paper shows that:Late Jurassic basins in the Chicheng—Xuanhua aera formed in the extrusion tectonic setting,of which were characterized by volcanic rocks’ adakite features in Tiaojishan formation,and formed in crustal thickening environment,and the sedimentary stratas of basins were controled by basin marginal thrusts during Tuchengzi period.The collective effects of ancient pacific plate’s NW-direction subduction andShangyi — Chicheng — Gubeikou faults’ Southward thrust accompanied dextral strike-slip are important factors that controled the formation of basin pattern.