The Characteristics Of Continental Crustal Evolution Of North-central Shanxi

The continental crust is an important object of study the Earth's evolution, the relationship between the formation and evolution of continental crust and the plate tectonics is the major frontier in the study of plate tectonics. The north-central Shanxi is located in a very special tectonic position, eastern part of which is the Taihang Mountain intraplate orogen belt, northeast part is close to the southern tip of the Yanshan intraplate orogenic belt, northern part is more than a hundred kilometers away from the northern margin of North China intraplate mobile belt and the western part is Ordos Basin, which is a stable block within North China Craton. For the complete strata outcrops, complex structural features, frequent magmatic activities and the obvious mineralization, the study area retains information of the evolution of continental crust during different periods and is a better place for researching continental crust evolution.Based on "sedimentary strata as frame, magmatic activity as indications, tectonic evolution as background", this paper confirms and comprehensively analyses the above-mentioned, and summarizes "the evolution model of continental crust of north-central Shanxi", which will help to improve the understanding of the formation and evolution of Shanxi plate and the process of the formation, evolution and destruction of the North China Craton.Through the intensive analysis of sedimentary strata construction sequence, the sequence of magmatic activity and the evolution of tectonic pattern, this paper determines the stage of its formation and the evolution period, summarizes and concludes the process of the formation and evolution of continental crust, and builds the model of formation and evolution.According to thinking about the founding of evolution model of the continental crust, this paper proposes three principles of founding the model of the study area(principle of continuous construction, distinct transformation and consistent dynamic background)and concludes and analyses comprehensively three ways of model-founding(analysis of the stratigraphic contact, sedimentary formation and magmatic formation, characteristics and sequence of deformation and the genetic relation), which helps developing new ideas and methods for the regional geological research.The paper chooses4strata sections for measuring from7field observation strata sections, builds strata column, determinates sedimentary formation sequence, in which basement, cap rocks, unconsolidated sediments, have distinctive sequence feature. And through the in-depth research, including field observation, systematical measurement, focused sampling and laboratory analysis, on the Mesozoic sedimentary strata of the Ningjing basin it has been found that from Jurassic Datong groups began to show the paleocurrent flowed to the southeast at some period, recording the information of uplift of western Ningjing Basin and propose the conclusion that the time of uplift of Northern Lvliangshan Mountain during the Mesozoic shouldn't be later than the Middle Jurassic Datong group. This new understanding will contribute to a better understanding of the evolution of Shanxi plate and North China basin during Mesozoic.Author Chooses different period magmatic rocks for investigating in order to dominate magmatic and structure sequence. After investigates9different period magmatic rocks which is Wutainian, Lvliang, Yanshanian and Himalayan. period, and founds their magma activity character and them been controlled by tectonics. By the end focused on2magmatic rocks for deeply researching. Author found that the formation period of Jushi mountain rock mass and Chafangkou stock group is1786Ma～1797Ma which belongs to Luliang period through field mapping,systematic sampling,observed by microscope,chemical analysis,zircon dating etc comprehensive means, corrected the wrong recognition that Jushi mountain rock mass is the production of Yanshan period of Mesozoic. Geochemical analysis shows that Jushi mountain rock mass and Chafangkou rock mass group are homologous, and conjecturing they are two branches of the same rock mass which is named Chafangkou-Jushi mountain rock mass. The new conclusion has important significance for the understanding of fault-fold belt magmatic of Xizhou Mountain. A focused investigation was done to Fansi basalt through outside investigation,field observation comparison sampling,chemical analysis etc. Study shows that the northern magma flew to the north while the southern to south which shows that the outpouring channel is in the rift valley of Hutuo River and found an evidence for the conjecture of previous. The rock geochemistry analysis also shows that Fanshi basalt belongs to alkaline basalt series and has the characteristics of continental-rift type volcanic, olivine inclusions growth in rock indicate that the magma came from upper mantle, and provide references for the research of north china craton.By determining deformation characteristics, deformation sequence and formation relation, author obtains evolution sequence of the structure pattern and residual state of basement structure pattern and distribution limitations. Mesozoic tectonic pattern controlled the region today landforms distribution. Cenozoic superimposed on top of the Mesozoic pattern. The three stages of the tectonic pattern reflect the dynamic background of the conversion process, and it is an important basis of the divided district inland crustal evolution stage.This paper proposes three principles of founding the model of the study area (principle of continuous construction, distinct transformation and consistent dynamic background) and concludes and analyses comprehensively three ways of model-founding (analysis of the stratigraphic contact, sedimentary formation and magmatic formation, characteristics and sequence of deformation and the genetic relation). The evolution process was divided into three stages: basement-forming stage,cover development stage and transformation-destruction stage; and a further divided into7evolution stages which are continental nucleus formation stage,landmass collision stage, basement transformation stage,cover formation stage,cover development stage, extrusion transformation stage and tension destruction stage. The continental formation evolution model of north central Shanxi was constructed through summary and the built of this model provides references for the geological evolution of north central Shanxi.