The Mesozoic Superimposed Tectonic Deformation And Evolutionary Processaround Changping-Huairou Area, North Of Beijing

Changping-Huairou area,in the north of Beijing,is located in the western part of the Yanshan orogenic belt.During the Mesozoic,strong tectonic deformation and extensive magmatic activities took place in the area.The predecessors have studied the NE trend tectonic traces a lot and less attention was paid to the NW tectonic traces.As a result thesuperposition relationship between NE and NW trend tectonic traceis not well researched,either.Tectonic deformation in different directions is very important to understand the whole tectonic evolution process of Yanshanorogenic in Mesozoic.So to find out the tectonic evolution of Mesozoic,a lot of works need to be done.This paper analyzed the complex geometrical and kinematic characteristics of the folds and faults,in different trends,of the study area;analyzed the truncation relationship among the different tectonic traces,and their relationship with intrusion,related rock and volcanic strata;recovered the paleo-stress field basing on counting fault sliding data,the Mesozoic evolution of tectonic deformation is analyzed.After all,we conclude their tectonic evolution of the process of superposition and transformation.The contraction deformation,in NW trend,is mainly characterized by a series of gentle folds,such as Tiekuangyu anticline and Huangyanshan anticline.The newest strata involved in the anticline is Ordovician,above it is the Tiaojishan Formation(161-153 Ma).This shows that the contraction deformation took place before 161 Ma.Then it was changed by the thrust,whose trend is NE,the whole appearance has been transformed into pieces.The contraction deformation,in NW trend,is the most intense,and can be divided into two periods.The former deformation period formed a series of NW-trend folds,such as the Huanghuacheng anticline and Badaohe syncline.The strata involved are the Changcheng System,Jixian System,Cambrian system,Ordovician System.The Badaohe Syncline Superimposed on the early NW-trend fold deformation.NE thrust faults developed mainly in the late stage.Such as the Shisanling-Shangzhuang-Hongluosi Thrust and the Dapian-Tiekuangyu Thrust.Thrust direction towards NW in general and in someplace towards NNW.Shisanling-Shangzhuang-Hongluosi Thrust is truncated by the Xuejiashiliang Granite(130Ma).Which means the contraction deformation happens before 130 Ma.The NNW contraction structure is mainly characterized by several fold deformations,Such as the Baihecun Fold and the Jundushan Anticline.The fold deformation involved the Wumishan Formation and Tiaojishan Formation.The folding deformation of Baihe Village has the kinematic polarity directed to SWW.The Jundushan Anticline superimposed on the Shisanling-Shangzhuang-Hongluosi Thrust,Thiscontraction structure active after 130 Ma.NW-trend fold deformation may be related to the subduction and collision of the Mongolia Okhotsk plate;the kinematics polarity of the NNW contraction deformation shows that the dynamicof this stage came from the east of the study area.