The Study Of Magma Mixing In Late Paleozoic Of Borohuoro In The West Tianshan Orogeny

The west Tianshan, which is located in the southwest of the Central Asian Orogenic Belt (CAOB), records the significant accretion of the CAOB. Numerous granitods with mafic enclaves are extensively developed in the Borohuoro region of the West Tianshan Orogeny, and preserve important evidence for the late Paleozoic tectonic evolution processes and continental growth.The zircon U-Pb ages of 373.8±2.0Ma and 371.5±2.5Ma were obtained from the Nileke and Sakesayi host granites, while 374.5±2.2Ma and 366.6±1.7Ma were obtained from their mafic enclaves, and they all formed in late Devonian. Poikilitic texture, disequilibrium magmatic textures, and needle-like apatite can be found in the mafic enclaves, indicating a two-end member magmatic mixing. The enclaves and host-granites present well linear relation in Huck diagram. At the same time, they have similar features in trace elements. Therefore, Petrography, geochronology, and geochemistry indicate the occurrence of magmatic mixing in Nileke and Sakesayi plution.Similar to Nileke and Sakesayi plution, Yuqibulake and Wutuinghe plution show magmatic mixing characteristics in Petrography, geochronology,and geochemistry as well. Meanwhile, the poikilitic texture and disequilibrium magmatic textures are more significant. The zircon U-Pb ages of 300.7±2.0Ma and 308.9±1.9Ma were obtained from the Yuqibulake granites and its mafic enclaves, while 303.1±1.5Ma and 297.4±2.9Ma were obtained from Wutujinghe. The contemporaneous granites with the same features are extensively developed in West Tianshan and surrounding areas, indicating a much larger scale of magama mixing.The host granites in Borohuoro enriched in LILE, such as Rb, Th, U, Pb, depleted in HFSE, especially depleted in Sr, Nb, Ta, P, Ti, suggest its affinity for continent crust source. Compared with the host granites, the enclaves show lower content of SiO2, K2O, and higher FeOT, MgO. The host granites in four plutons with positive ?Hf(t) and Neoproterozoic model age indicate a mixing between partial melting Neoproterozoic juvenile crust and depleted lithospheric mantle.Nileke, Sakesayi and other granites with arc features and mantle components show local tension due to enlarged of the subduction angle during late Devonian. Yuqibulake and numberous grnitetods show that the environment has transformed from post-collision to extension in late Carboniferous.Nileke, Sakesayi, Yuqibulake and Wutujinghe plution are magma-mixing type granites produced by the mixing of acidic magma of the crust source and basic magma of the mantle source, which indicates the continental crustal growth of the South Tianshan through the joining of the mantle material in late Devonian, as well as in late Carboniferous.