ZIRCON U-Pb GEOCHRONOLOGY,Hf ISOTOPIC COMPOSITION AND RE-GIONAL TECTONIC IMPLICATION OF CENOZOIC HIGH POTASSIC GRA-NITIC INTRUSIONS IN THE XUELONGSHAN MASSIF,WESTERN YUNNAN
This paper presents a study of structural deformation,zircon U-Pb and Hf isotopes,rock geo-chemistry,and petrogenesis analysis to understand the mylonitic high-potassium granitic dykes in the Xue-longshan complex,aiming to constrain the Cenozoic tectonic evolution of the northern section of the Ailaoshan-Honghe Shear Zone.The zircon U-Pb dating of three granitic dyke samples reveals Cenozoic a-ges of 34.8±0.4 Ma,35.4±0.3 Ma,and 32.6±0.2 Ma.The εHf(t)values of the zircons range from+7.8 to+8.6,+3.7 to+7.0,and+6.3 to+9.2,respectively,with second-stage model ages between 563-658 Ma,664-876 Ma,and 524-706 Ma,suggesting that the magma source is juvenile mafic lower crust.Geochemical analysis shows that the three granitic dykes have similar characteristics,with high w(SiO2)content(70.14％-73.74％)and low w(MgO)content(0.07％-0.84％),w(Y)(3.92×10-6-8.66×10-6)and w(Yb)(0.27 × 10-6-0.77 × 10-6).They also exhibit high Sr/Y ratios(42.54-129.18)and low Na2O/K2O ratios(0.82-1.66),indicative of adakitic or adakitic-like magmatic proper-ties.Comprehensive analysis indicates that during the Eocene-Oligocene,the thickened lower crust in the Sanjiang area experienced gravitational instability.The subsequent collision-induced separation of plate fragments triggered the upwelling of deep mantle material,leading to the thickening and melting of the crust.This process generated adakitic or adakitic-like high-potassium magma.Zircons from different sta-ges of the ancient Tethys Ocean's evolution were captured or inherited during magmatic emplacement.Combining this with rock deformation analysis,it is proposed that the Cenozoic left-lateral strike-slip shear of the Ailaoshan-Honghe Shear Zone occurred after 32.6 Ma.
Xuelongshan massifzircon U-Pb and Hf isotopic analysispetrological and chemical analy-sishigh-potassic granitic intrusionAilaoshan-Red River Shear Zone
万方数据
维普
