Electrical conductors in Archean mantle—Result of plume interaction?

Abstract

From long‐period magnetotelluric data across the Gawler Craton, we obtain a three‐dimensional resistivity image of the lithosphere and provide constraints on tectonothermal events dating back to the Proterozoic. Contrary to common observations of Archean cratons displaying high electrical resistivity in the mantle lithosphere, the magnetotelluric data show low resistivity of around 10Ω m at 80km depth underneath the 1595Ma Gawler Range Volcanics, a silicic large igneous province. The resistivity distribution appears to be a signature of plume‐modified orogenesis with low‐degree partial melting at the base of the lithosphere in a back‐arc setting. The enhanced conductivity is explained through higher hydrogen and iron content in the crystal lattice and also along the grain boundaries of the mantle constituting minerals. Older, arc‐related magmatism to the southwest across 1620–1610Ma St. Peter Suite does not display enhanced conductivity and suggests a depleted mantle lithosphere. The data show that Yellowstone‐type mantle plume analogues are preserved through time and still display an elevated electrical signature in the lithosphere today.