Publication 132

Electrical conductivity of continental lithospheric mantle from integrated geophysical and petrological modeling: application to the Kaapvaal Craton and Rehoboth Terrane, southern Africa.

Fullea, J., M.R. Muller, and A.G. Jones

Abstract

The electrical conductivity of mantle minerals 1 is highly sensitive to parameters that characterize the structure and state of the lithosphere and sub-lithospheric mantle and mapping its lateral and vertical variations gives insights into formation and deformation processes. We review state-of-art conductivity models based on laboratory studies for the most relevant upper mantle minerals and define a bulk conductivity model for the upper mantle which accounts for temperature, pressure and compositional variations. The bulk electrical conductivity model has been integrated into the software package LitMod, which allows for petrological and geophysical modeling of the lithosphere and sub-lithospheric upper mantle within an internally consistent thermodynamic-geophysical framework. We apply our methodology to model the upper mantle thermal structure and hydrous state of the western block of the Archean Kaapvaal Craton and the Proterozoic Rehoboth Terrane, in southern Africa, integrating different geophysical and petrological observables: namely elevation, surface heat flow, magnetotelluric, and xenolith data. We find that to fit the measured magnetotelluric responses in both the Kaapvaal and Rehoboth terranes the uppermost depleted part of the lithosphere has to be wetter than the lowermost melt metasomatized and refertilized lithospheric mantle. We estimate a present-day thermal lithosphere-asthenosphere boundary depth of 230-260 km and 150�20 km for the western block of the Kaapvaal and Rehoboth terranes respectively. For the Kaapvaal, the depth of the present-day thermal LAB differs significantly from the chemical LAB, as defined by the base of a depleted mantle, which might represent an upper level of melt percolation and accumulation within the lower lithosphere.

Source

Journal of Geophysical Research - Solid Earth, 116, B10202, doi:10.1029/2011JB008544. [PDF]

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Alan G Jones / 18 October 2011 / alan(at)cp.dias.ie