Genesis And Tectonic Properties Of Jinjiling Rock Mass In Nanling

Nanling area is characterized by large-scale diagenesis and mineralization,the granitic rocks and related metal deposits are widely developed.In recent years,there are many achievements of diagenesis and mineralization in this area,howerer,the Yanshanian tectonic attribution and magmatic evolution in Nanling area remain highly controversial.This subject take the Jinjiling pluton,which located in the western section of Nanling tectonic magma belt as research object,based on the methods of lithogeochemistry,isotope geochemistry,mineral chemistry and zircon U-Pb geochronology to explore the the reasons of genesis and tectonic properties of the Jinjiling rock mass,further provides a reference for the evolution of Yanshanian rock mass and the evaluation of metallogenic potential in Nanling area.LA–ICP–MS zircon U–Pb ages indicate that the complement fine-grained monzogranite and body coarse-to medium-grained porphyritic syengranite of the Jinjiling pluton are the products of magmatic activity in the early Yanshanian,which crystallized at 156.4±0.66Ma and 153.0±2.2Ma,respectively,and the diagenetic age of the former is later than that of the latter.The biotite from Jinjiling pluton is magmatic biotites,which belongs to siderophyllite and protolithionite,the sericite is hydrothermal mica,which belongs to zinnwaldite.The emplacement pressure of biotite in coarse-to medium-grained porphyritic syengranite is2.77?4.52 kbar,the emplacement depth is greater than 10km and the crystallization temperature is 530?680?.The biotite of the coarse-to medium-grained porphyritic syengranite and fine-grained monzogranite fell into QFM-HM and NNO-HM,respectively,suggesting that the increase of oxygen fugidity in complement granite is conducive to the crystallization and mineralization of cassilite magnetite.The Jinjiling pluton has typical geochemical properties of A-type granite,for example,the Jinjiling pluton is characterized by rich silicone-alkali and poor calcium-magnesium,which belongs to metaluminous-peraluminous granite.The samples have high ratios of Ga/Al(×10⁴),Fe O*/Mg O and the contents of Zr+Nb+Ce+Y as well as the zircon saturation temperature,and depleted in Ba,Sr,P,Nb and Ti.The main pluton has higher rare earth element content(REE),LREE/HREE and(La/Yb)_Nratio than the complement pluton.The differentiation index(DI)of the two types of granites is 88.76?94.39,90.68?95.87 and the?Eu values is 0.049?0.063,0.03?0.007,respectively,and the negative Eu anomalies of fine-grained monzogranite is very severe.The complement pluton has no obvious fractionation of light and heavy rare earth and showed a REE tetrad effect.The Jinjiling pluton has a high initial ⁸⁷Sr/⁸⁶Sr ratio(Sr_i=0.71258?0.73251),and low?_Nd(t)(-5.83?-11.63)and?_Hf(t)(-3.6?-7.3)values,suggested that the source area are crustal argillaceous rocks and graywacke;The Nd and Hf model ages are 1084?1556Ma and 1427?1661Ma,respectively,indicated that the source rocks separated from the mantle reservoir in the Mesoproterozoic.Combined with the geological evolution history of Nanling area,the tectonic background of Jinjiling pluton is the intracontinental extensional environment caused by the low-angle subduction of the Pacific Plate.