The production of parallel world-class W and Cu metallogenic belts linked to an asymmetric slab window

Abstract

The ca. 150−135 Ma magmatic belts in the Middle−Lower Yangtze River Valley and its southern adjacent parallel northeastern Jiangnan Orogen in China experienced large-scale Cu and W metallogenesis, respectively. The magmatic belts interrupted contemporaneous magmatism along the east China continental margin and are an ideal locality to verify if Cu and W metallogenesis could be linked to a slab window. Oceanic plate subduction, intracontinental extension, lower crustal delamination, or ridge subduction models have been debated for the Cu and W belts. However, these models have weaknesses that cannot explain unique features of the belts such as the belts being coeval and intersecting with the trend of the paleo-trench, or the asymmetric distribution of the magmatic-metallogenic belts along both sides of the Middle−Lower Yangtze River Valley. Based on the configurative, compositional, and isotopic evidences, the magmatic belts record the fingerprints of the slab window generated by disassembly of the paleo-ridge between the Paleo-Pacific and Izanagi plates at ca. 150−135 Ma. During this time, the Paleo-Pacific plate rolled back beneath the eastern margin of the South China block and the Izanagi plate experienced flat-slab subduction that reached beneath the intracontinental regions of the North China block. The distinct and contrasting behaviors of the slabs produced a slab window that caused and promoted upwelling mantle to flow farther southward, inducing the asymmetric magmatic-metallogenic belts along the Middle−Lower Yangtze River Valley on both sides. The Middle−Lower Yangtze River Valley Cu-enriched magmatic belt was formed by melting of the lower crust and oceanic slab edge along the ridge by upwelling asthenospheric mantle. However, the Jiangnan Orogen W-enriched magmatic belt was induced by melting of the accretionary belt and mixing the melting of accretionary belt and the same hybrid mantle materials, during which the upwelling asthenospheric mantle tongue infiltrated southward due to the asymmetric structure of the slab window.