The zircon U-Pb dating and geochemistry of the Baosuose Granite in the Northern Sanjiang Orogenic Belt and their geological significances
The orogenic process of the Sanjiang compound orogenic belt is characterized with the long-term and multi-period.Based on the U-Pb isotopes and trace elements of zircons and petrogeochemical characteristics of the Baosuose granite,in this paper,we have preliminarily discussed the formation background of the granite and its significance in the Sanjiang collisional orogenic process.The U-Pb isotopic ages of two zircon samples in the granite by using the LA-ICP-MS U-Pb dating method are(49.61±0.74)Ma and(48.48±0.59)Ma,respectively.Further research on petrogeochemistry and trace elements of zircons shows that there is relatively low content of residual plagioclase in the magma source whose residual phase consisting of major amphibole and minor garnet.By using the zircon saturation thermometer,it is estimated that the magma original temperature should be＞800 ℃.It is believed that the magma should be originated from the partial melting of basic igneous rocks in the lower crust under high temperature and high pressure.In the evolution process of magma,the wallrock assimilation-contamination and the fractional crystallization of plagioclase and amphibole occurred in the magma.Based on the comprehensive analysis,it is believed that the Baosuose granite belongs to the anatexis high potassium calc-alkaline I-type granite,which was formed in the post-collision environment.The U-Pb isotopic ages provide time limit for the collisional orogeny in this area.These mean that at about 50 Ma,although the Indo-Eurasian collisional orogeny had not ended yet,the Jinsha River area where the granite is located was in the post-collision extensional orogenic setting.
万方数据
维普
