3-D lithospheric conductivity structures in the Cathaysia Block and the Jiangnan suture zone: implications for origins of metallogenic belts

Abstract

Influenced by the subduction of the Izanagi plate, the South China Block underwent explosive mineralization in the Mesozoic, and a series of important ore concentration areas and metallogenic belts, such as the Nanling metallogenic belt (NMB) and northeastern Jiangxi metallogenic Province (NJMP), were formed in the Early Jurassic. The NMB is composed of a series of non-ferrous metal deposits and rare earth element deposits. The ore-forming rock source of the NMB is granite that mainly originated crustal partial melting and mantle material rising in the Mesozoic. The NJMP consists of a series of copper, lead, zinc, gold and silver deposits associated with acid volcanic and intrusive rocks. The boundary fault zone between the Yangtze Block and the Jiangnan orogenic belt penetrates into the mantle. As certain mantle materials have participated in the ore-forming diagenesis, both the NMB and NJMP benefited from the crust-mantle mixed sources. To study the deep electrical structures and metallogenic types of the NMB and NJMP, 333 magnetotelluric (MT) stations in the eastern part of South China were employed to obtain a lithospheric 3-D electrical structure model. The results show a low-resistivity anomaly extending from the mantle to the crust beneath the NJMP, which is explained as a magma channel of ore-formed materials. The upper crust of the NJMP has high resistivity, and it has been affected by large regional faults, such as the northeastern Jiangxi fault. The low-resistivity bodies in the mantle and crust of the NMB are connected by small low-resistivity channels, which could be pathways of upwelling asthenosphereic materials. According to the 3-D electrical structure model, the deep upwelling asthenospheric materials beneath the NMB were blocked by the high-resistivity lower crust. The heat and metallogenic elements from the mantle upwelling may have triggered partial melting of the overlying crust and crust-mantle mixing, resulting in the formation of non-ferrous metal deposits such as tungsten, tin and rare earth elements. The low-resistivity anomaly zones of the NMB and the NJMP connected with upwelling low-resistivity deep anomalies may reflect shallow deposits.