Lithosphere structure and its implications for the metallogenesis of the Nanling Range, South China: Constraints from 3-D magnetotelluric imaging

Abstract

We have obtained a lithospheric electrical resistivity model of the Nanling Range through 3-D inversion of magnetotelluric data from 118 sites comprising an array covering this important metallogenic belt. Approximately divided by longitude 114°E, the western and eastern parts of this area show significantly different lithospheric electrical features, spatially coincident with its west-east differential Jurassic metallogeny. The lithosphere beneath western Nanling is mainly characterized by high-resistivity, but with an approximately north–south trending, lithosphere-scale, nearly upright, high-conductivity zone that occurs beneath the Qin-Hang magmatic belt. We interpret this high-conductively zone to be a long-lived lithospheric weak zone being located on an ancient plate-boundary that experienced multiple reactivations. The zone controlled Jurassic mafic magmatic events, e.g., 174–176 Ma Daoxian and 150–154 Ma Ningyuan, and also acted as a narrow pathway for the rapid upwelling of hot and volatile-rich asthenosphere-derived materials during the Middle-Late Jurassic Cu-Mo/Pb-Zn mineralization. In contrast, to the east of longitude 114° E, a nearly 80 km deep, clear and continuous electrical lithosphere-asthenosphere boundary is imaged, which could result from a major lithospheric delamination event, probably caused by the early Paleozoic Wuyi-Yunkai orogeny and subsequent post-orogenic collapse, or the subduction and rollback of the Pacific slab after the Triassic. The eastern Nanling region with its thinned lithosphere is suggested as allowing broader zones of upwelling asthenospheric during the intensive Jurassic W-Sn metallogenesis, causing slow upwelling and lateral spreading of asthenosphere-derived materials and subsequent strong extension of the crust and also the mixing and assimilation with melts. Consequently, metallic elements were extensively extracted from the crust, eventually giving rise to the world-class W-Sn deposits in the eastern Nanling region.