Cenozoic Adakite-type Volcanic Rocks in Qiangtang,Tibet and Its Significance  

作　　者：LIUShen HURuizhong FENGCaixia CHIXiaoguo LICai YANGRihong WANGTianwu JINWei 

机构地区：[1]GuiyangInstituteofGeochemistry,ChineseAcademyofSciences,Guiyang,Guizhou550002 [2]GraduateSchooloftheChineseAcademyofSciences,Beijing100039 [3]CollegeofEarthSciences,JilinUniversity,Changchun,Jilin130026 [4]AeroGeophysical&RemotesensingCenter,Beijing100083

出　　处：《Acta Geologica Sinica(English Edition)》2003年第2期187-193,共7页地质学报（英文版）

基　　金：supported jointly by"the Ninth Five-Year Plan"key basic research program(Grant No.9501101-5);the Project of Knowledge Innovation sponsored by the Chinese Academy of Scienoes(Grant No.KZCX2-102;the National Outstanding Young Scientists Fund Project(Grant No.49925309)

摘　　要：Volcanic rocks in the study area, including dacite, trachyandesite and mugearite, belong to the intermediate-acid, high-K calc-alkaline series, and possess the characteristics of adakite. The geochemistry of the rocks shows that the rocks are characterized by SiO2>59%, enrichment in A12O3(15.09-15.64%) and Na2O (>3.6%), high Sr (649-885 μg/g) and Sc, low Y contents (<17 μg/g), depletion in HREE (Yb<1.22 μg/g), (La/Yb)N>25, Sr/Y>40, MgO<3% (Mg<0.35), weak Eu anomaly (Eu/Eu=0.84-0.94), and lack of the high field strength elements (HFSE) (Nb, Ta, Ti, etc.). The Nd and Sr isotope data (87Sr/86Sr=0.7062-0.7079, 143Nd/144Nd=0.51166-0.51253, εNd= -18.61-0.02), show that the magma resulted from partial melting (10%-40%) of newly underplated basaltic lower crust under high pressure (1-4 GPa), and the petrogenesis is obviously affected by the crust's assimilation and fractional crystallization (AFC). This research will give an insight into the uplift mechanism of the Tibetan plateau.Volcanic rocks in the study area, including dacite, trachyandesite and mugearite, belong to the intermediate-acid, high-K calc-alkaline series, and possess the characteristics of adakite. The geochemistry of the rocks shows that the rocks are characterized by SiO2>59%, enrichment in A12O3(15.09-15.64%) and Na2O (>3.6%), high Sr (649-885 μg/g) and Sc, low Y contents (<17 μg/g), depletion in HREE (Yb<1.22 μg/g), (La/Yb)N>25, Sr/Y>40, MgO<3% (Mg<0.35), weak Eu anomaly (Eu/Eu=0.84-0.94), and lack of the high field strength elements (HFSE) (Nb, Ta, Ti, etc.). The Nd and Sr isotope data (87Sr/86Sr=0.7062-0.7079, 143Nd/144Nd=0.51166-0.51253, εNd= -18.61-0.02), show that the magma resulted from partial melting (10%-40%) of newly underplated basaltic lower crust under high pressure (1-4 GPa), and the petrogenesis is obviously affected by the crust's assimilation and fractional crystallization (AFC). This research will give an insight into the uplift mechanism of the Tibetan plateau.

关 键 词：CENOZOIC lower crust high-K calc-alkaline volcanic rock UNDERPLATING partial melting uplift of plateau QIANGTANG TIBET 

分 类 号：P588.14[天文地球—岩石学]