Electrical conductors in Archean mantle—Result of plume interaction?

Abstract

[1] 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 10 m at 80 km depth underneath the 1595 Ma 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 1620-1610 Ma 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.

Electrical Resistivity Maps of the Australian Lower Crust

“…As continental upper mantle is largely comprised of olivine at temperatures below 1000 C, laboratory measurements suggest resistivities will be of order 10 3 .m or more. Exceptions may be due to electrical conduction in hydrated minerals (Selway, 2014;Thiel and Heinson, 2013) or some other mechanism that may enhance conduction to as low as 1 .m in places. However, as the mantle fertility state is likely to be over distance -scales of hundreds of kilometres, variations in upper mantle resistivity cannot explain the heterogeneous induction arrow response.…”

Imaging the electrical lithosphere of South Australia - 2D profiles and preliminary results of AusLAMP SA

“…Tectonic activity between 1.8-1.5 Ga has significantly shaped the Gawler Craton through multiple magmatic events making the eastern margin of the Gawler Craton prospective. The footprint of this event in the lithosphere is evident from previous 3D magnetotelluric investigation highlighting enhanced conductivity at depths greater than 80 km (Thiel and Heinson, 2013). Liberation of fluids from a deep plume source is a likely explanation for transporting fluids and other minor conducting phases from the mantle to the surface (Griffin et al, 2013).…”

Evolving 3D lithospheric resistivity models across southern Australia derived from AusLAMP MT

“…At a period of 1000 s (Figure 2), very large scale trends become apparent in the electrical structure across the state. The Gawler Craton can be divided into two distinct zones, the central southern region has very distinct ellipses varying in orientation of NE-SW to NNE-SSW with minimum phase angles of about 45 degrees or higher and hint toward the large conductivity anomaly at mantle depths observed by Thiel and Heinson (2013). The rest of the Gawler Craton is defined by phase angles less than 45 degrees and occur on the outer edges of the Gawler Craton, with the exception of the high phase angle circular ellipses of the Eyre Conductivity Anomaly.…”