| 南祁连北缘东段早志留世刚察大寺花岗岩的成因——锆石LA-ICP-MS U-Pb年代学和岩石地球化学制约 |
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| 关键词:Early Silurian granite zircon U-Pb dating geochemistry Gangchadasi South Qilian block |
| 基金项目:中国地质调查局地调工作项目(编号: 1212011221145); 教育部新世纪优秀人才支持计划(编号: NCET-12-0237)和国家自然科学基金(编号: 41472052) |
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| Petrogenesis of Early Silurian Gangchadasi Granites in the Eastern Segment of the Northern South Qilian Block: Constraints from LA-ICP-MS Zircon U-Pb Geochronology and Geochemistry |
| The formation age and petrogenesis of the Gangchadasi granites in the eastern segment of the northern South Qilian block remain controversial. New LA-ICP-MS zircon U-Pb dating and whole-rock geochemical analysis were conducted in this study to constrain the petrogenetic and tectonic processes during the formation of the granites. The Gangchadasi granites are mainly composed of granodiorite and biotite-monzogranite. Zircons from the granodiorite show euhedral shape, oscillatory CL zoning and high Th/U ratios (0.27 ~ 0.91), indicative of a magmatic origin. The weighted mean of the youngest group of concordant 206Pb/238U ages yielded an emplacement age of (435±4) Ma. The granodiorite and biotite-monzogranite share similar geochemical characteristics, such as high content of SiO2 (65.52% ~ 74.23%), total alkali ((Na2O+K2O)=6.95% ~ 8.24%), and aluminum (Al2O3=12.33% ~ 15.26%), and low amounts of magnesium (MgO=0.31% ~ 1.32%). Their A/CNK ratios range from 0.85 to 1.05, indicating a transitional composition between metaluminous and peraluminous. The granites are enriched in large ion lithophile elements (e.g., Rb, Ba, and K) and light rare earth elements and depleted in high field strength elements (e.g., Nb and Ta) and heavy rare earth elements, and exhibit prominent negative Eu anomaly (δEu=0.51 ~ 0.80) and depletion of Sr, P, and Ti. It is held that the Gangchadasi granites are I-type granites derived from partial melting of a middle-upper continental crust under the condition of high temperatures and low pressures. In combination with regional tectonic evolution, the authors suggest that the Gangchadasi granites probably formed in an active continental margin during Early Silurian. |
| SHI Jiang-peng,HUO Teng-fei,LAI Qiang,PENG Xiang-hua,DU Sun-yan,YANG De-bin.2015.Petrogenesis of Early Silurian Gangchadasi Granites in the Eastern Segment of the Northern South Qilian Block: Constraints from LA-ICP-MS Zircon U-Pb Geochronology and Geochemistry[J].Acta Geoscientica Sinica,36(6):781-789. |
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