Relationship between electrical conductivity, metallogeny, and lithospheric structure in South China

The South China Block (SCB) is located at the junction of the Pacific, Eurasian, and Tethys plates. Their interaction led to large-scale multi-stage mineralization in the SCB during the Mesozoic. Several regional ore-concentration areas, such as the Middle-Lower Yangtze metallogenic belt (MLYMB), the Wuyishan metallogenic belt (WYMB), the Nanling metallogenic belt (NLMB), and the Qinzhou-Hangzhou Metallogenic Belt (QHMB) were formed during this process. However, the mineral types of these metallogenic belts are different. To study the deep mechanisms of the different metallogenic types developed in the same tectonic background at almost the same period, the magnetotelluric sounding (MT) data from 691 sites located mainly within the eastern SCB (Fig.1) are employed to obtain a regional lithospheric 3-D resistivity model.

According to this model, Large-scale low-resistivity bodies extend from the crust to the upper mantle beneath the MLYMB and the QHMB, which are interpreted as channels of upper mantle upwelling. While the upper- to mid-crust beneath the WYMB and the NLMB is characterized by high resistivity with small-scale low-resistivity anomalies, indicating upwelling mantle materials having invaded the crust on a small scale. Large-scale upper mantle low-resistivity anomalies extend along its strike direction beneath the MLYMB and the QHMB. It could be concluded from the resistivity model that deep low-resistivity anomalies and mantle upwelling channels mainly controlled almost all the Mesozoic deposits(Fig.3). However, the scales of low-resistivity anomalies and upper-crust ore-controlling structures are different. Significantly, the upper-mantle low-resistivity anomalies beneath the eastern SCB show a spatial distribution that is gradually shallowing from south to north, probably indicating that the asthenospheric materials are upwelling from south to north, corresponding with the changing progressively of magma and metallogenic activities. We propose that the lithospheric delamination and asthenospheric upwelling caused by the far-field effects of the paleo-Pacific Plate subduction are the source of solid magmatic activities and related metallogeny (Fig.3).

* This work was jointly supported by the China Geological Survey project (DD20160082 and DD20190012) and the SINOPROBE project.

Fig. 1 Distribution of MT stations within the study area. The metallogenic belts after Yan et al. (2021).

Fig.2 Horizontal slices of 3-D resistivity model. Deposit data after Mao et al. (2018).

 Fig.3 A comprehensive 3-D diagram illustrating the possible formation mechanism of the metallogenic belts.

References

Mao, J., Xie, G., Yuan, S., Liu, P., Meng, X., Zhou, Z., & Zheng, W. (2018). Current research progress and future trends of porphyry-skarn copper and granite-related tin polymetallic deposits in the Circum Pacific metallogenic belts. Acta Petrologica Sinica, 34(9), 3-19.

Yan, J., Lü, Q., Luo, F., Cheng, S., Zhang, K., Zhang, Y., et al. (2021). A gravity and magnetic study of lithospheric architecture and structures of South China with implications for the distribution of plutons and mineral systems of the main metallogenic belts. Journal of Asian Earth Sciences, 221, 104938.