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Geology and Magma-Dynamical Features of Jingjiling Composite Granitic Batholith in the Western Nanling Region

ZHANG Bang-tong, DAI Yong-Shan, WANG Ju, BAI Chou-Yong, LIU Hong-lei   

  1. Department of Earth Sciences and State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing 210093, China
  • Received:2001-03-20 Revised:2001-03-20 Online:2001-03-20 Published:2001-03-20

Abstract: Jinjling composite batholith in the west Nanling Region consists of three granite bodies with different ages of intrusion: I stage,amphibole-bearing biotite adamellite; Ⅱ stage,biotite granite; II stage,two-mica granite. The ages and initial strontium ratios for the I stage andⅡ stage granites by Rb-Sr whole-rock isochron method are 169 .5 Ma and 0.7163, and 150.7 Ma and 0.7206,respectively. It indicates that they are intrusions of early Yanshanian period. Granites of the Jinjiling hatholith belong to calc-alkaline rock series and show a general evolution trend from I stage admmellite, to Ⅱ stagegranite and Ⅲ stage bimicaceous granite as follows: aluminium saturation index increases from metaluminous(I)to peraluminous(Ⅱ)and highly peraluminous; ordering degree of K-feldspar increases from 0.33(I) to 0.69(Ⅱ)and 0.80(Ⅲ); An of plagiaclase decreases from 37(I)to 26(Ⅱ)and 7(Ⅲ); chemical composition of biotite varies from Fe-hiotite(I),to lepidomelane(Ⅱ)and Fe-mica(Ⅲ); oxides (Si02, Al2O3 ,TFe,MgO,TiO,CaO)versus DI diagrams show a linear evolution features; rock-forming temperatures gradually drop down form 745℃(I) to 673℃(Ⅱ) and 505℃(Ⅲ). By means of geochemical and geobarometric methods,it is estimated that the depth of emplacement for Jinjiling batholith was about 6.5km, and the rock-forming pressure was about 180MPa Jinjiling composite granitic batholith belongs to S-type granitoids,forming in collision orogeny environment.