[S-IT15] Mass and energy transport properties and processes in the crust and the mantle

[SIT15-03] Electrical properties of carbonate-bearing slab and mantle rocks

*Emmanuel Codillo¹, Anne Pommier¹, Ming Hao ¹, Michael Walter ¹, Andrew Thomson ², Rajdeep Dasgupta ³, Bjorn Mysen¹ (1.Earth and Planets Laboratory, Carnegie Institution for Science, USA, 2.Department of Earth Sciences, University College London, UK, 3.Department of Earth, Environmental and Planetary Sciences, Rice University, USA)

Keywords:electrical conductivity , carbonate melts , volatiles

Carbonate-rich melts are key components of the deep carbon cycle, and their transport can influence the geochemical and geophysical characteristics of the Earth’s interior. These melts are thought to form at the incipient melting of carbonated peridotite and subducted carbonated crustal materials at depths within the redox stability of carbonate minerals. Using petrological and experimental constraints, their presence and distribution in the upper mantle have been inferred from the elevated mantle electrical conductivity from electromagnetic measurements. Small amounts (0.035–0.35 vol. %) of interconnected carbonate melt have been invoked to explain the observed high mantle conductivity values down to 300 km depth. However, whether a continuous network of carbonate melt exists at depths where elevated mantle conductivity is observed remains debated. We conducted laboratory experiments using impedance spectroscopy in a multi-anvil press to determine the electrical conductivity of carbonated peridotite and carbonated basalt over a large range of P-T conditions (7–15 GPa, and up to 1600 °C). Electrical results are interpreted using electron microprobe analyses on the starting materials and retrieved samples as well as the phase relations previously determined at the P-T conditions of the electrical experiments. This approach allows relating the conductivity variations to subsolidus and melting processes. At subsolidus conditions, conductivity increases with increasing temperature (>10^-2 to >10 S/m). At temperatures above the solidus, electrical conductivity values are reproduced satisfactorily with a formalism that accounts for chemical variations and the amount of partial melt. Implications of our results are discussed in terms of carbonate-rich magma migration and the carbon cycling at depth.