Deep electrical structure and geological significance of Tongling ore district

- Profiles reveal three kinds of crustal structures crossing different tectonic units.
- Mesozoic extensive magma activity formed high-resistivity-bodies.
- The two-layer electrical structure presents a typically half graben basin.
- The homogeneous low-resistivity layers present a normal lower crust model.

The Tongling ore district is one of the most important Cu-polymetal producers in the Lower Yangtze River metallogenic belt of China. To understand deep crust structure beneath the Tongling ore district more comprehensively and objectively and to explore important scientific issues, such as characteristics of lithospheric evolution, the relationship between the crustal structure and metallogenesis, it is necessary to study the variation of crust electrical structure in the study area. For this purpose, six magnetotelluric (MT) sounding profiles have been completed by SinoProbe-03 Project. Based on the imaging results of the six profiles, electrical conductivity structure of the crust has been analyzed. The result shows that the geology beneath the profiles is characterized by layering in vertical direction and block division in horizontal direction. The high-resistivity features are related to the transparent zones detected at the upper crust in reflection seismic surveys. The absence of reflectivity from the depths indicates a homogeneous zone, which could often be related to granitic intrusions. Combining the regional tectonic evolution, MT and other geophysical data, we suggest that the high-resistivity bodies crossing the Tongling uplift reveals the center of magma activity and the layering in vertical direction in the lower crust reveals a normal lower crust model and propose a small-scale underplating model which is different with both the “partial melting of a thickened or delaminated lower continental crust” model and the “oceanic ridge subduction”. The underplating might be related to small-scale lithospheric or lower crust delamination controlled by deep fault during the Early Cretaceous. The result of this MT survey is important for constraining lithospheric evolution and metallogenesis in the Lower Yangtze Metallogenic Belt, such as collision of North China Craton and Yangtze Craton, underplating models, deep structure, mechanisms of NE-SW trending rift as well as graben basin, and probable metallogenesis.