Geochemical Characteristics And Geological Significance Of The North And South Of Granodiorite Porphyry Dikes Group In Haojing District,Beishan District,Inner Mongolia

The Beishan area of Inner Mongolia is located at the western border of China,and the study area is located at the southern side of the baiheshan-pengboshan ophiolite belt.The magmatic activities in the area have the characteristics of long evolution time,complex rock types and variable tectonic backgrounds.This paper selects the Biaoshan area to the north and south of granodiorite porphyry dikes as the main research object.On the basis of field observation,this paper studies its geological characteristics,petrogeochemical characteristics and geological age characteristics,combines the previous research data and the characteristics of tectonic-magmatic activity in the adjacent area,and discusses its magma source,forming age and geotectonic environment.It is generally believed that the formation of dyke swarms is mainly related to the extensional tectonic environment,often representing the rift environment,which represents the beginning of the plate movement cycle.Comparing with the typical dike swarms in the world,it is found that the dike swarms differ greatly in scale and lithological characteristics,so it is presumed that they do not represent the beginning of plate movement cycle.The author found that the granodiorite porphyry stocks emerged in the southeastern part of the dyke swarms.The geochemical characteristics of the stocks are very similar to those of the granodiorite porphyry stocks.Both of them have obvious characteristics of poor potassium and rich sodium,and have characteristics of quasi-aluminous to weak peraluminous.A/CNK is 1.01-1.04,and their magma differentiation degree is higher,with DI=79.07-84.28.Their total REE varies greatly,light REE enrichment type,light and heavy REE differentiation degree is higher,REE=?45.52-65.53?×10^-6,LREE/HREE=9.81-16.07;Europium in rocks shows slightly positive anomaly,the average value of?Eu is 1.03;Ce shows slightly negative anomaly,?Ce=0.83-1.00;trace elements have the characteristics of low content of Rb,Ba and Nb.By LA-ICP-MS zircon U-Pb dating,the weighted average age of granodiorite porphyry dyke swarms is 372.1?±3.2Ma?,which is the Late Devonian,and the weighted average age of granodiorite porphyry swarms is 364?±1.7Ma?,which is also the Late Devonian.Therefore,the author considers that the dyke swarms and the granodiorite porphyry stock are the same magma source.This study shows that the Late Devonian granodiorite porphyry belongs to type I granite,which was formed in the post-collision compressive tectonic environment.There was post-collision magmatic acticity in the Biaoshan area of the Late Devonian.At this time,beishan area entered the stage of post-collision extensional tectonic evolution.