Opportunistic magnetotelluric transects from 3D CSEM surveys in the SW Barents Sea

Magnetotelluric (MT) data allow for electrical resistivity probing of the earth’s subsurface. Integration of resistivity models in passive margin studies could help disambiguate non-unique interpretations of crustal lithologies from seismic and potential field data. In this contribution, we present the first marine MT data in the Barents Sea, derived from industrial controlled-source electromagnetic (CSEM) surveys and characterize its quality, dimensionality and depth penetration to elaborate a modelling strategy. This MT database consists of 337 receivers located along 7 regional transects, emanating from ~70,000 km² of 3D CSEM surveys acquired for hydrocarbon exploration from 2007 to 2019. High-quality MT data are extracted for periods ranging from 0.5 s to 5000 s with no apparent contamination by the active source, nor effects related to large time-gaps in data collection and variable solar activity. Along receiver profiles, abrupt lateral variations of apparent resistivity and phase trends coincide with major structural boundaries and underline the geological information contained in the data. Dimensionality analysis reveals a dichotomy between the “western” domain of the SW Barents Sea, dominated by a single N-S electromagnetic strike, and the “eastern” domain, with a two-fold, period-dependent strike. 35 receivers show 3D distortion caused by nearby bathymetric slopes, evidenced by elevated skew angle values. We delimit geographical areas where the 2D assumption is tenable and lay the foundation for future 2D and 3D MT modelling strategies in the SW Barents Sea. We performed 2D MT inversion along one of the regional transects, a ~220 km-long, E-W profile encompassing a major structural high and distal basin approaching the continent-ocean boundary. The resistivity model shows low crustal resistivity values (1-10 Ω.m) beneath the sedimentary cover in western distal basins, in stark contrast with high resistivity values (1000 - 5000 Ω.m) of the thick crystalline crust in the proximal domain on the structural high. We interpret this abrupt lateral resistivity variation as a crustal necking zone with a rapid transition to a hyperextended continental crust. In the proximal domain, a 50-100 Ω.m and 20 km-wide, intra-crust vertical contact hints at a plausible paleo-plate suture. Integration of resistivity with velocity, density and magnetic susceptibility models will further refine these tectonic models and related processes in the SW Barents Sea margin. Our methodology is applicable globally where 3D CSEM surveys are acquired and has a large potential for harvesting new knowledge on the electrical resistivity properties of the lithosphere.