GEOCHEMISTRY AND LITHOLOGY OF THE SHIPENGYU SUPER-UNIT IN DASHIQIAO,LIAONING PROVINCE

Shipengyu super-unit,distributed in the north of Dashiqiao,Liaoning Province,is tectonically located in the west part of the Yingkou-kuandian anteclise,adjecent to the Xialiaohe fault depression.The rock is the result of the tectonomagmatic activities of Yanshanian period,with a whole rock Rb-Sr isochron age of 186±13Ma.It has a close genetic relationship with the Fenshui gold ore field and the Jinshanling lead deposit.The chemical component of the super unit rock is characterized by high Si and alkali and low Ca and Mg,to reflect alkaline rock.The content of trace elements also shows the characteristics of alkaline granite,that is rich in Ga,Nb,Ce,Y,Zr,Mo and W and poor in Co,Ni,Cr,V,Sc and Sr.The ΣREE is lower than the average value of the acid rock defined by A.L.Venogradov(1962) and the granite by A.G.Hermann(1970),suggesting typical LREE enrichment type.By chemistry conversion of natural minerals of the granite,the rock of Shipengyu super-unit is proved to be alkali feldspar granite.The main type of the super-unit rock is biotite alkali feldspar granite.The Sr and O isotopic features show that the diagenetic substance of Shipengyu super-unit is formed by the magma,which has been derived from upper mantle and partly melts the substance of lower crust.The rock is formed in the intraplate extensional environment in Early Jurassic or Yanshanian period,genetically belonging to the A-type nonorogenic granite.