Petrogenesis And Geological Significance Of The Dazeshan Pluton,Jiaodong Peninsula

Jiaodong Peninsula is the most important gold provinces in China.Currently,the proven gold resources account for about a quarter of the country,and more than 95%of it is deposited in the northwestern area of Jiaodong.Banded distribution of the Early Cretaceous granitic pluton and nearby Late Jurassic granitic pluton.The Early Cretaceous granitic schist in the southwestern part of Jiao has little exposed on the surface,only the Dazeshan pluton intruding into the Linglong pluton in the form of a pluton is found,and the Early Cretaceous granitic pluton in the north The body has similar geological characteristics.However,there is still no systematic research on the structural background,diagenetic age and its relationship with the gold deposit formed by this pluton.Therefore,this paper is based on detailed field geological survey and observation under indoor microscope.Carried out systematic petrography,zircon U-Pb chronology and geochemistry,discussed the genesis and geological significance of the pluton,and gained the following knowledge:?1?The lithology of the Dazeshan pluton is clearly divided,The marginal facies are medium-fine-grained dolomite granites,and the central facies are porphyritic granites.The porphyry of the porphyritic granite is potash feldspar.The zircon U-Pb chronology shows that the age of porphyritic granite is?119.6±1.3-120±1Ma?,and the age of dark inclusions is?119±2Ma?.?2?The SiO₂ content of the pluton mass is 69.01%-77.45%,with high total alkali,which belongs to high-potassium-rich alkali,quasi-aluminum to weak over aluminous pluton.Enrich LREE and lose HREE,enrich LILE,no obvious europium anomaly,?La/Yb?N=5.19%?47.88%,light and heavy rare earth elements are strongly differentiated,Ba and Sr content is high,reflecting high Ba-Sr The geochemical characteristics of granite.The dark-colored inclusions have similar geochemical characteristics to the host pluton.?3?The T_2DM of the Sr-Nd isotope of the Dazeshan pluton is?2497-2723Ma?.Combining chronological and geochemical characteristics,it is preliminarily believed that the Dazeshan pluton is formed by the bottom melting of the remelted Yangtze plate middle and lower crust parts and the early mantle-derived basic magma.The paleo-Pacific plate subducted towards the North China plate and caused the upwelling of the asthenosphere material as the most likely tectonic setting for the Dazeshan pluton diagenesis.?4?The large-scale metallogenesis of the Jiaodong Northwest gold deposit is between 130 and 100 Ma,which is consistent with the diagenetic age of the Dazeshan pluton?120 Ma?,and more than 95%of the gold deposits existed in the Early Cretaceous granitic pluton mass and The late Jurassic granitic pluton nearby indicates that magma mixing occurred in the lower crust and mantle of the North China Plate in the late Early Cretaceous and promoted a series of processes of gold element upward flow-enrichment-precipitation and mineralization.