Origin And Its Geological Significance Of Carboniferous-permian Hypabyssal Intermediate-acid Plutons In The Awulale Area,West Tianshan

The Central Asian Orogenic Belt(CAOB)is one of the most prominent areas in the global development of the continental crust.The western Tianshan is located in the southwest part of the Central Asian orogenic belt.There are a large number of Late Paleozoic shallow intrusive rocks exposedin the eastern Awulale area which are the ideal objects to discuss tectonic evolution of the Late Paleozoic and the continental crustal growth.LA-ICP-MS U-Pb zircon dating for Aikendaban rock porphyric-like granite,2752Gaodi dioritic porphyrite,Wudaikendaban monzogranite and diorite as well as Arixian porphyric-like granite yield 282 Ma,307 Ma,249 Ma 306Ma and 304 Ma,respectively..All four plutons occure as a small plutons with the porphyritic/porphyritic structure.The Arixian pluton is characterized by the metaluminous calcalkaline rocks,while others belong to metaluminous to weakly peraluminous high-k calcalkaline rocks.They have highly consistent geochemical features,showing enrichment in LREE and LILE and poor HFSE,moderate and weak negative Eu anomalies,depletion of Nb,Ta,P,Ti and Sr elements,similar to the geochemical characteristics of the crust-derived arc magmatism.Aikendaban porphyritic-like granite and 2752 Gaodi diorite porphyrite have ?Hf(t)of 3.2?11.8 and 3.2?11.7,respectively,and corresponding TDMC is 548?879 Ma and 572?877 Ma.The sHf(t)of the Wudaikendaban monzogranite and diorite range from 6.78 to 14 and 4.24 to 13.55,and TDMC from 295 Ma to 432 Ma and 286 Ma to 508 Ma.Arixian granite show sHf(t)of 4.48?10.63 and TDMC of 379?533Ma.They have positive ?Hf(t)values and slightly high TDMC than their forming ages,indicating partial melting from the Neoproterozoic-early Paleozoic crustal material.Four plutons,together with regional coeval small plutons,were formed during the later period of large-scale crust-mantle granitic magmatism in west Tianshan,suggesting a weakening of the large-scale granitic magmatism from late Carboniferous to middle Permian.Based on the comprehensive analysis for late Paleozoic granitoid magmatism in west Tianshan,the occurrence of these small plutons represented an intermediate-acid magmatism from late Carboniferous to middle Permian,implying a decreasing of large-scale magmatism in the transitional stage from post-collision to intra-continental extension,being an important turning point of the deep dynamical background and the tectonic environment in west Tianshan.