Geochronology, geochemistry and tectonic significances of the Hongyuntan granitoids in the Qoltag area, Eastern Tianshan
Wu, CZ and Zhang, ZZ and Zaw, K and Della-Pasqua, FN and Tang, JH and Zheng, YC and Wang, CS and San, JZ, Geochronology, geochemistry and tectonic significances of the Hongyuntan granitoids in the Qoltag area, Eastern Tianshan, Acta Petrologica Sinica, 22, (5) pp. 1121-1134. ISSN 1000-0569 (2006) [Refereed Article]
Paleozoic igneous rocks and mineral deposits are keys to revealing the tectonic setting of the Qoltag belt in Eastern Tianshan, Xinjiang Province. Investigation in petrology, mineralogy and geochemistry indicates that the Hongyuntan granitoids at the southern margin of the Qoltag area are typical Cale-Alkaline volcanic arc granitoids, and have genetic relation with melting of the lower crust affected by subduction of the oceanic crust. U-Pb age determinations of Zircon by LAM-ICP/MS show the Hongyuntan granitoids were intruded at 328.5 ± 9.3 Ma of Middle Carboniferous. By contrast, magmatism in the Middle Tianshan, south of the Qoltag area is not important. In the late Paleozoic of the Qoltag area, mineral deposits show zonal distribution with its southern margin being dominated by Fe deposits of the volcanosedimentary and hydrothermal type, and its northern margin being dominated by Cu-Mo deposits of the porphyry type. In combination with distribution of the volcanosedimentary strata and tectonic evolution of the Qoltag and its surrounding areas, it is suggested that a Qoltag ocean occurred in the Paleozoic. In early Paleozoic, the Paleo-Qoltag ocean subducted southward beneath the northern margin of the Tarim plate, resulting in the Middle Tianshan island arc. While in late Paleozoic, the Qoltag ocean changed in subduction polarity and decent northward beneath the Junggar-turpan-Hami block. The Hongyuntan granitoids were thus formed in this volcanic arc setting above the subducting Qoltag ocean crust of late Paleozoic in association with other Hercynian magmatic rocks, volcanosedimentary strata, and zonally distributed mineral deposits.