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Geodynamic significance of the A-type granites in the Sawuer region in west Junggar, Xinjiang Rock geochemistry and SHRIMP zircon age evidence [查看] ZHOUTaofa、YUANFeng、TANLugui、FANYu、YUEShucang

Sawuer region is located in west Junggar, Jimunai County of Altay district and Hefeng County of Tacheng district, Xinjiang. The region is along the north margin of Kazakstan-Junggar plate. The intrusions (mainly acid) are widespread. Qiaqihai and Kuoyitasi intrusions are important in the region, with the characteristics of A-type granite. Fu rther investigations indicate that they belong to A2-type granite that formed in extension tectonic setting of post collision. The REE chon-drite-normalized patterns of the intrusions show LREE enrichment and theδEu values are lower. The Nd, Sr, Pb isotope compositions of the intrusions indicate a mantle source, while the low δ18O values resulted from the isotope exchange between intrusion and meteoric water. According to SHRIMP U-Pb age analysis results, the crystallization age of Qiaqihai intrusion is 290.7±9.3 Ma (1σ), and that of Kuoyitasi intrusion is 297.9 ± 4.6 Ma (1σ), corresponding to the beginning of early Permian. The A2-type granites indicate that the region was in the extension period of the post- collisional stage at the beginning of early Permian in the Sawuer region. The A-type granites in the Sawuer region in west Junggar discovered from this work is analogous to the A-type granites found in east Junggar of the Ulungur alkali granites belt. The c onfirmation of post-collisional A-type granites of early Permian in the Sawuer region provides new evidence for the regional vertical continental crust growth in early Per-mian. The former proposed Ulungur alkali granites belt can extend from east Ulungur through west Ulungur and to Zhaisang in Kazakstan westwards.