Electrical Conductivity of Carbonated Rocks: Constraints on Carbonate Melt Distribution and Transport in the Upper Mantle

Carbonate melts play a crucial role in the deep carbon cycle, influencing both the geochemical evolution and geophysical properties of Earth’s interior. These melts are thought to form during the incipient melting of carbonated peridotite and subducted carbonated crustal materials at depths corresponding to the redox stability field of carbonate minerals. Evidence for the presence of carbonate melts in the upper mantle - down to depths of approximately 300 km - has been inferred from regions of anomalously high electrical conductivity detected by electromagnetic surveys. However, estimates of melt abundance at these depths vary widely: seismic studies typically suggest higher melt fractions than those inferred from electromagnetic data. This discrepancy hinders our understanding of melt distribution and transport in the mantle.

In this talk, I will present new electrical conductivity measurements on carbonated peridotite and carbonated basalt conducted from subsolidus to supersolidus conditions (7 - 15 GPa and up to 1585°C) to examine the conductivity response associated with the onset of carbonate melting. Measurements were performed using impedance spectroscopy in a multi-anvil press, and results are interpreted through integrated analyses of the starting materials and quenched samples, conductivity mixing models, and established phase relations at the experimental pressure-temperature conditions. Using these new data, I re-evaluate estimates of melt content in the mantle and propose that, at the spatial resolution probed by electromagnetic surveys, channelized carbonate melts within a depleted mantle are unlikely to significantly enhance bulk mantle conductivity. Finally, I will discuss the implications of these findings for reconciling electrical and seismological observations, understanding carbonate-rich magma migration, and exploring future opportunities to investigate the electrical properties of magmas and rocks under high-pressure and high-temperature conditions at Stanford.

Speaker: Emmanuel Codillo, Stanford University

Room: 350/372

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