Volcanism and mineralization in the North Qilian Orogenic Belt, Northwestern China

Abstract

The bedrocks of the North Qilian Mountains have been subjected to episodes of continental rifting, ocean basin opening subduction, basin closing and plate collisions. This has, resulted in a diversity of volcanic rocks that were deposited from the Proterozoic to the Silurian in the North Qilian orogenic belt. Proterozoic continental rift volcanism produced flood basalts in the western parts of the North Qilian Mountains, with Fe and Cu as the major mineral resources. Cambrian volcanic rocks are rift-related, and can be divided into two groups based on their textural characteristics (flow dome complexes versus fissure complexes) and their associations with Cu deposits. Early Paleozoic submarine mid-ocean ridge volcanic rocks are preserved as obducted slices of the North Qilian ocean basin. The subduction complex which marks the site of the Paleozoic paleo-trench is located on the northeastern side of the Paleozoic submarine volcanic belt. A Late Cambro-Ordovician belt of arc-related volcanic rocks is located to the northeast of the subduction complex, along the southern Zhulang Moutains. Middle-Late Ordovician volcanism occurred in a back-arc basin setting, as exposed on the northern slope of Zhulangnanshan. Within this back-arc environment, ophiolite suites developed with Cu and Zn deposits hosted in basic lava in the upper parts of the ophilites. Late Ordovician volcanism occurred in a passive continental rift setting with minor Cu- and Pb-Zn sulfide mineralization.