STUDY OF GEOCHRONOLOGY,GEOCHEMICAL CHARACTERISTICS AND GEOLOGICAL IMPLICATION OF QUARTZ DIORITE IN MINGSHUI AREA,BEISHAN,GANSU PROVINCE
In this paper,we investigate the whole rock geochemistry,petrology,zircon U-Pb geochro-nology and Lu-Hf isotope analysis,to understand the rock formation age,genesis and geological implica-tion of quartz diorite and porphyritic quartz diorite in Mingshui area,Beishan,Gansu Province.The re-sults indicate that these rocks are quasi-aluminous,high-potassium,calc-alkaline Ⅰ-type granites with high silica content(w(SiO2)=56.88％-67.78％)and are rich in aluminum(w(Al2O3)=14.26％-18.15％).The total alkali content is moderate(w(K2O+Na2O)=4.97％-6.80％),and the K2O/Na2O ratio ran-ges from 0.78 to 1.46,which is characteristic of weakly peraluminous rocks(A/CNK=0.90-1.03).In terms of trace elements,the rocks show significant depletion in high field strength elements such as Nb,Ta,and Ti,while they are enriched in large ion lithophile elements such as Rb,Th,and K,resembling the geochemical characteristics of typical volcanic arc magmatic rocks.The chondrite-normalized rare earth element(REE)curves are asymmetrical and right-leaning,showing strong fractionation(LREE/HREE=8.59-23.41)and a weak negative Eu anomaly(δEu=0.74-0.96).LA-ICP-MS zircon U-Pb dating of the Mingshui quartz diorite indicates a Middle-Late Carboniferous age of 311.8±1.51 Ma.Additionally,the quartz diorite has a positive εHf(t)value(2.08-4.48)and a relatively young Hf model age(TDM=746-863 Ma),suggesting that the magma originated from the partial melting of the overlying young crust due to mantle magma infiltration.Our comprehensive analysis concludes that the Mingshui quartz diorite and porphyritic quartz diorite formed in a continental marginal arc environment during the subduction of the middle Hercynian period,as direct products of the southward subduction of the Hongshishan ocean.
万方数据
维普
