Petrogenesis Of The Haojiagou Intermediate-acid Intrusive Complex And Its Tectonic Implications Within Shangyi Country,Northern Hebei Area

Based on the systematic field geological survey,petrography,geochemistry and zircon u-pb chronology of the Intermediate-acid intrusive complex in haojiagou,shangyi,northern hebei province,this paper provides a basis for further exploration of the tectonic evolution of the northern margin of the north China craton.The Haojiagou Intermediate-acid intrusive complex in Shangyi,northern Hebei Province,is located in the middle part of the northern margin of the North China Craton and the north side of the Shangyi-Chicheng fault zone.The main lithologies of Intermediate-acid intrusive complex are gneissic granite and gneissic diorite.The gneissic granite is divided into two intrusive bodies,one is in Daba Gou-Changgou area in the west,with the NWW direction;the other is in Hanqingba-Dashan Jingou area in the east,with the NEE direction,which the main rock type is biotite monzonite The gneissic diorite is also divided into two intrusive bodies,one is in the Haojiagou area in the west,which nearly spreading out with the NWW direction.the other is in the gneissic granite body in the NW direction,and the other is in the Hanqingba-Dashan trench area in the east.Gneissic diorite intruded into gneissic granite body,the main rock types are biotite diorite and gneissic diorite,The plagioclase in gneissic diorite is neutral plagioclase,and the chemical characteristics of amphibole minerals are magnesia amphibole.The gneissic granite body has high silicon content?69.26%⁷5.81%?,alkali-rich?Na₂O+K₂O=0.21%¹.01%?,iron?Fe^T=1.74%².35%?,aluminum saturation index?A/CNK=0.99¹.03?,which is quasi-aluminous-weak peraluminous granite.The Ritman index?1.74².52?belongs to calc-alkaline.Gneissic granite is rich in Rb,K and other high-field strength elements,such as high-ion lithophile elements and Th,U,etc.It is obviously deficient in Ba and Sr.It shows that light rare earth is relatively rich and heavy rare earth is deficient.La/Yb=1.51-4.84 indicates that light and heavy rare earth fractionation is high and has obvious negative Eu anomaly??Eu=0.19-0.24?.Gneissic diorite has high silicon content of 52.94%⁶0.61%,rich potassium?1.86%².27%?and sodium?3.08%³.73%?,quasi-aluminous?A/CNK=0.78⁰.99?,Ritman index?1.76².11?,belonging to calc-alkaline.The total REE content of rocks?119.43×10-6²01.4×10-6?shows weak negative Eu anomalies??Eu=0.14⁰.72?,?La/Yb?_N values range from 4.74 to 16.98,and rock differentiation is not high.Zircon U-Pb ages of gneissic granites are 245±2.3Ma,245.7±1.8 Ma and zircon U-Pb ages of gneissic diorites are 246.2±3.1 Ma,suggesting that they were formed in the Early Triassic and were the product of magmatic evolution of Indosinian epoch.The gneissic granite is of type A₂,which is located at the junction area of post-collision and intraplate on the Rb-Y+Nb discriminant map.This indicates that the formation of the intermediate-acid complex in Haojiagou,Shangyi,may be related to the extension after the closure of the Paleo-Asian Ocean,and is a response to the Indosinian tectonic evolution in the middle part of the northern margin of the North China Craton.