Syn-collision Biotite Hornblende Granodiorite from the Zedong Area,Tibet:Zircon U–Pb Isotope Chronology,Petro-geochemistry,and Geodynamic Significance  

作　　者：ZHU Feilin SHI Zeming XIONG Fuhao NI Shijun BAI Mei 

机构地区：[1]College of Earth Science,Chengdu University of Technology,Chengdu 610059,Sichuan,China [2]Applied Nuclear Technology in Geosciences Key Laboratory of Sichuan Province(Chengdu University ofTechnology),Chengdu 610059,Sichuan,China [3]Geological Survery lnstitute,Chengdu University of Technology,Chengdu 610059,Sichuan,China

出　　处：《Acta Geologica Sinica(English Edition)》2017年第2期515-529,共15页地质学报（英文版）

基　　金：financially supported by China Geological Survey(grant no.12120113095700,12120101000015001108);the National Science Foundation of China(grant no.41403039);the training program for young and middle aged backbone teachers of Chengdu Universcechnology(grant no.KYGG201502)

摘　　要：Cu–Au mineralization is rare in the Jurassic–Early Tertiary batholiths related to the India–Asia collision. Geochemical analysis and U–Pb isotope chronology was carried out on Shuangbujiere biotite hornblende granodiorite from the Zedong area. Zircon grains of the biotite hornblende granodiorite show oscillatory growth zonation and have high Th/U ratios of 1.08–2.39, indicating a magmatic origin for the zircons. Geochrological test yielded a LA-ICP-MS U-Pb age of 51.5±1.0 Ma, suggesting that the emplacement age of the biotite hornblende granodiorite is Early Eocene. The Shuangbujiere biotite hornblende granodiorites have geochemical features characteristic of adakite and are associated with a calc–alkaline metaluminous I-type granite enriched in Sr, high in Mg~#（49.6–54.9） and Sr/Y, and depleted in Y and Yb. These results indicate that this intrusion formation may have been associated with crustal thickening caused by the early collision of the Indian and Eurasian Plates. As the process of crustal thickening continued, the heating of the underplated basaltic magma caused the thickened lower crust amphibolite to dehydrate the melt and form a high-K calc–alkaline adakitic melt at about 848°C. Meanwhile, magma mixing of the underplated basaltic melt and high-K calc–alkaline adakitic melt formed a high-Mg# adakite representative of the sys-collisional tectonic setting.Cu–Au mineralization is rare in the Jurassic–Early Tertiary batholiths related to the India–Asia collision. Geochemical analysis and U–Pb isotope chronology was carried out on Shuangbujiere biotite hornblende granodiorite from the Zedong area. Zircon grains of the biotite hornblende granodiorite show oscillatory growth zonation and have high Th/U ratios of 1.08–2.39, indicating a magmatic origin for the zircons. Geochrological test yielded a LA-ICP-MS U-Pb age of 51.5±1.0 Ma, suggesting that the emplacement age of the biotite hornblende granodiorite is Early Eocene. The Shuangbujiere biotite hornblende granodiorites have geochemical features characteristic of adakite and are associated with a calc–alkaline metaluminous I-type granite enriched in Sr, high in Mg~#（49.6–54.9） and Sr/Y, and depleted in Y and Yb. These results indicate that this intrusion formation may have been associated with crustal thickening caused by the early collision of the Indian and Eurasian Plates. As the process of crustal thickening continued, the heating of the underplated basaltic magma caused the thickened lower crust amphibolite to dehydrate the melt and form a high-K calc–alkaline adakitic melt at about 848°C. Meanwhile, magma mixing of the underplated basaltic melt and high-K calc–alkaline adakitic melt formed a high-Mg# adakite representative of the sys-collisional tectonic setting.

关 键 词：CHRONOLOGY ADAKITE thickened lower crust Zedong orefield Gangdese TIBET Proto-Tethys 

分 类 号：P588.122[天文地球—岩石学] P542[天文地球—地质学]