The lower crust conductor from Nanjing (Ning) – Wuhu (Wu) area in the Middle and Lower Reaches of Yangtze River: Preliminary results from 3D inversion of magnetotelluric data

• Lower crust conductivity existed in the test area.
• ‘Local melt’ or ‘shear zone’ may exist in the lower crust.
• The deep Yangtze River Fault is a group of several shallow and deep faults.
• The deep Yangtze River Fault may be associated with upper-mantle uplift.

A series of long magnetotelluric (MT) profiles across the Ning-Wu Basin and adjacent areas were deployed by SINOPROBE-03 deep drilling project and 3D exploration technology integration project from 2011 to 2012. Broadband MT data were acquired at 349 sites with a frequency range of 0.0003–320 Hz. Preliminary three-dimensional inversion of this dataset revealed a striking feature of extensive areas with high conductivity in the lower crust. Combined with regional heat flow results, relative water content was calculated from the resistivity model, suggesting that a ‘local melt’ or ‘shear fracture’ may exist in the lower crust, which is likely to be hot and weak. The location of the upper mantle uplift and Yangtze River deep fault were hence inferred from the electrical properties. Furthermore, the Yangtze River Fault may be composed of a number of minor faults.