Three-dimensional electrical resistivity structure beneath the Cuonadong dome in the Northern Himalayas revealed by magnetotelluric data and its implication

The North Himalayan gneiss domes (NHGD), as one of the extensional structures widely distributed across the southern Tibetan Plateau, are an important window for studying post-collisional diastrophism and magmation as well as polymetallic mineralization. However, the deep mechanism for the formation of NHGD remains controversial. The magneto-telluric (MT) method was adopted to study the deep structure of the Cuonadong dome in the Northern Himalayas. The characteristics of the dome were explored by using the MT sounding curves and phase tensors. Three-dimensional (3D) MT inversion was performed to determine the electrical resistivity structure beneath the Cuonadong dome. The preferred 3D electrical resistivity model shows that an obvious low-resistivity anomaly develops beneath the Cuonadong dome which is overlaid by a high-resistivity body and surrounded by an apparent subcircular zone of low-resistivity anomalies. The integrated conductivity (longitudinal conductance) from depths of 1-20 km indicates that the average longitudinal conductance at the core of the Cuonadong dome is about 10,000 S. The high-conductivity anomaly at the core is found to be analogous to that of lava, mainly resulting from the crustal partial melting, and the estimated melt content is 11.0-17.3%. The high conductance surrounding the dome reaches 20,000 S on average, which is mainly attributed to saline fluids. MT results in this study support that the Cuonadong dome experienced magmatic diapirism. Taken together with previous geological and geochemical studies, we suggest that under the east-west (E-W) extensional tectonic setting in southern Tibet, deep crustal partial melting constantly accumulated beneath the dome, and therefore the magmatic diapirism resulted in the formation of the Cuonadong dome. In addition, the MT results also indicate that the development of the Cuonadong dome provides abundant mineralizing fluids and the space for migration of metallogenic fluids for (rare-metal) polymetallic mineralization.