Geochemical Characteristics,Chronology Of Badaling Granitoid Complex And Their Geodynamic Significance

The Badaling granitoid complex is located in the northern margin of the North China Craton.The Badaling granite is composed of 121 intrusions,and is divided into eight units.The lithology varied from basic rocks to acid rocks(including gabbro,diorite,quartz monzonite,quartz-syenite,monzodiorite,monzonitic granite,granite and alkaline granite,etc.).Badaling granite is also one of the earliest reported of adakites in our country,and contains four types of granite(Adakitic-type,Zhemin-type,Guangxi-type and Nanling-type).So,we select Badaling granite as our research object,hope to be able to do some concrete work in the research of the Badaling granite.1.This paper for the first time identified late indosinian granite(the age of 203 Ma and 202 Ma and 198 Ma)from Badaling granite.This article named it Huata pluton,and separated it from Badaling granite.Huata pluton exposed in the north of Huata village Nankou town Changping district,on the west side of the road from Nankou to Juyongguan.Huata pluton is very special,it is a kind of high Sr and Yb type granite(Guangxi type)with less exposed in nature.This suggested source area without plagioclase and garnet in the residual phase,and mainly composed of amphibole and pyroxene,belong to high temperature granites.2.We made 17 pieces of isotope analysis data and 60 pieces of geochemical analysis from different intrusions of the Badaling granite.In this paper,we discuss their era,geochemical characteristics and geodynamic significance of different types of granites.3.Badaling includes three kinds of granites during the period from late Jurassic to early Cretaceous:Adakitic-type monzonitic granite(146-130Ma),Zhemin-type granite(150-143Ma,133-130Ma)and Nanling type granite(157-140Ma,128Ma).4.The occurrence of Badaling different types of granites reflects the change of crustal thickness:during the process of magma evolution in the late Triassic to early Jurassic period(203?198Ma),Guangxi-type of granite suggests the Badaling area with normal crustal thickness and the temperature is very high when the magma formed.In 157-140Ma,during the late Jurassic-early Cretaceous,crust thickness is normal or thinner than before.During 144?140Ma,Adakitic type,Zhemin-type and Nanling type granite appear in the Badaling area.These data may reflect the crustal thickness changed and the crustal thickness begins to thicken during this period.During 140?130Ma,give priority to adakitic type granite,the Badaling area was under thickened crustal background and was part of eastern China plateau.During 133-130Ma,adakitic type and Zhemin type granite exposed,that means the crust began to collapse.After 128Ma,the crustal thickness thinned in the Badaling area.5.Badaling is located in the northern margin of North China Craton,some granite data surrounding shows that crust of the northern margin of north China thickened in the early cretaceous,after 130 Ma,crust thinned.The North China Craton collapsed and went into extensional tectonic background.