Sedimentation and mineralization of the Late Paleozoic extensional basin in the western Kunlun Mountains, China

Abstract

In the western Kunlun Mountain region, due to the convergence of the Paleotethys Ocean in the Late Paleozoic, through northward subduction towards the West Kunlun Block, forming the Kangxiwa–Waqia arc magmatism and back-arc extensional basins, including the Tamu–Kalangu and Oytag–Kurliang basins. This study explores the relationship between basin evolution and mineralization. First, the Late Paleozoic back-arc and far-field continental back-arc basins were distinguished by analyzing sediment constructions in the basins. The former was continuously deposited in the Middle Devonian–Late Permian above the Precambrian basement due to the existence of the depressions. The latter were intermittently deposited in the Middle Devonian–Late Permian due to rifting above the Caledonian orogenic belt. Although the two settings were separated by the Tiekelike fault, their formations were subject to mantle upwelling caused by the subduction of the Kangxiwa oceanic crust. We also divided the Hercynian and Indosinian magmatic activities related to the basin; the former of which included the formation of bimodal magmatic rocks (339–291 Ma) as the basin expanded, which resulted in hydrothermal sediments and hydrothermal–magmatic mineralization, mainly including volcanic massive copper sulfide, Cu and Ni sulfide, and hydrothermal deposits. During the Indosinian orogeny, intermediate acidic magmatic rocks (265–206 Ma) associated with the closure of the basin was formed, leading to the development of hydrothermal Cu–polymetallic and porphyritic copper deposits. The relationship between basin evolution and mineralization was determined. Based on the findings, we concluded that the basin extended between the Middle Devonian and Early Permian. Syngenetic sedimentary deposits formed in the closed basins and anoxic environments of local depressions and mainly included sedimentary rock-hosted stratiform Cu deposits, exhalation-sedimentary Pb–Zn deposits, and sedimentary Mn deposits. Between the Middle Permian and Early Triassic, the basin began to close and the transformation from a basin to a mountain range finally occurred. The sedimentary basement was transformed by folding and faulting, thus forming tectonic deposits, including hydrothermal vein-type Pb–Zn deposits and Cu–Pb deposits within tectonically altered rocks. The results of this work show that the Late Paleozoic extensional tectonic environment formed both the back-arc basin and the far-field continental basin simultaneously. Periods of magmatism related to rifting and convergence could be distinguished by the corresponding mineralization. The metallogenic types related to the basin could also be divided into sedimentary, magmatic hydrothermal and tectonic hydrothermal deposits.