Petrogenesis and tectonic implications of A -type granites in the Kattasay region, Middle Tianshan, Uzbekistan

Petrogenesis of A -type granites has played an important role in revealing their geological settings. Granite intrusions in the Kattasay region, mainly consisting of quartz porphyry and alkali -feldspar granite porphyry, are located within the Chatkal-Kurama volcano -plutonic zone in the Middle Tianshan of Uzbekistan. LA-ICP-MS zircon U-Pb dating yields ages of ca. 297. 3Ma for quartz porphyry and ca. 294. 5Ma for alkali -feldspar granite porphyry, respectively. The quartz porphyry and alkali -feldspar granite porphyry show high SiO2(70. 14% similar to 75. 78%) and K-2 0 + Na2O (8. 07% -10. 48%) contents, and they also have high FeOT/(FeOT + MgO) (0. 88 similar to 0. 94) ratios. All of them have high 10000Ga/A1 (2.51 similar to 3. 14) ratios and Zr + Nb + Y + Ce (439.5 x 10 (-6) -1141 x 10(-6)) values and show an affinity to A -type granites. These rocks display similar trace elemental patterns, showing pronounced positive Rb-KTh-U anomalies and negative Ba-Sr-Ti-Nb-Ta anomalies, implying that they have experienced advanced fractional crystallization. Based on the analysis of isotopic compositions, these samples display variously positive epsilon(HF) ( t) values of + 0. 06 similar to + 5. 03 and negative epsilon(Nd) ( t) values of . 21 similar to - 3. 24. The decoupling between Nb and Hf isotopes indicates the presence of a magma mixing. The quartz porphyry has analogical ages, similar geochemical features and isotopic compositions with alkali -feldspar granite porphyry, which suggests they might be derived from the similar source. The recognition of Kattasy A -type granites suggest that the Turkestan Ocean was ultimately closed at the end of the Late Carboniferous, while the Middle Tianshan was in a post-collisional environment in the Early Permian.