Age, composition, and tectonic significance of Palaeozoic granites in the Altyn orogenic belt, China

ABSTRACTWe examined the petrography, litho-geochemistry, and geochronology of granite plutons in the Altyn orogenic belt, northern margin of the Qinghai–Tibet Plateau, to investigate the geodynamic history of the belt. The granites are peraluminous, with variable chondrite-normalized rare earth element patterns but generally similar trace element compositions; all are depleted in Ba, Nb, Sr, P, and Ti, and enriched in Rb, Th, Ta, Zr, and Hf. Their U–Pb zircon ages record multiple magmatic episodes between 500 and 404 Ma (north Altyn block (NAB)), 522 and 432 Ma (central Altyn block (CAB)), and 483 and 226 Ma (south Altyn block (SAB)). We propose a geodynamic model for the Altyn orogenic belt. Prior to 467 Ma, the north Altyn Ocean subducted southward below the NAB. The north Altyn region saw a change from subduction to collision between the Dunhuang block and the NAB during 467–450 Ma. The collision lasted until 430 Ma and was followed by post-collisional extension until 400 Ma. Farther south, the central...