Detrital zircon record of continental collision: Assembly of the Qilian Orogen, China

Abstract

The Qilian Orogen, Northwest China, preserves a record of Early to Middle Paleozoic subduction and collision between the Central Qilian Block and North China Craton through closure of the intervening Late Neoproterozoic to Early Paleozoic North Qilian Ocean. Ordovician strata in the Hexi-Corridor Basin document the initial collisional history with a change in tectonic setting from retro-arc to foreland basin. Ages of zircons from the Upper Ordovician strata range from Archean to early Paleozoic with prominent peaks at around 2.5 Ga, 1.6 Ga, 1.0 Ga, and 0.47 Ga. The early Paleozoic ages are consistent with the time of magmatic arc activity related to northward subduction of the Qilian Ocean. Precambrian grains are restricted to the upper part of the sampled sections, with the proportion of Paleozoic grains descending up the section. This trend is interpreted to reflect the gradual termination of subduction zone magmatism and the swamping of the basin by material from the colliding Central Qilian Block and North China Craton. Archean and the early Proterozoic detritus were likely derived from the North China Craton to the north, whereas the Central Qilian Block to the south provided the late Proterozoic grains. Silurian and Devonian strata within the Hexi-Corridor Basin continue to show this mixed source provenance with depositional environment changing from a flysch to molasse setting.