Melting from 1000°C and geophysical discontinuities in the shallow Earth’s mantle
Abstract
Numerous geophysical studies reported low seismic velocity and high electrical conductivity anomalies in the shallow, oceanic upper mantle of the Earth, at a level sometimes referred to as the Gutenberg discontinuity. This discontinuity is commonly interpreted to mark the onset of partial melting in the mantle, and also to correspond to the lithosphere-asthenosphere boundary (LAB), where the decoupling of the cold and rigid plates from the hot and convecting mantle drives plate tectonics. From petrological experiments and modelling, we determined the melting temperature of the mantle with relevant CO₂ and H₂O contents, which can be as low as ~1000°C. We evidence that Earth's mantle does start melting at pressures and temperatures corresponding to the Gutenberg discontinuity. However, this discontinuity is clearly located within the lithosphere, at about two thirds of its thickness, and thus does not represent the LAB. The low temperatures (down to ~1000°C) and the low fractions of melts at the Gutenberg discontinuity do not lower the viscosity of the mantle significantly. The LAB lies deeper at much higher temperatures (~1300-1400°C) where melting has progressed. This indicates it is not the onset of melting but the increase in melt fraction at the transition from volatile-to silicate-controlled melting that reduces mantle viscosity so as to drive plate tectonics at the LAB.
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BibTeX
@article{gardes2026melting,
title = {{Melting from 1000°C and geophysical discontinuities in the shallow Earth’s mantle}},
author = {Emmanuel Gardés and Mickael Laumonier and Tahar Hammouda and Geeth Manthilake},
journal = {Earth and Planetary Science Letters},
year = {2026},
month = oct,
doi = {10.1016/j.epsl.2026.120006},
url = {https://hal.science/hal-05834917v1},
note = {CC BY-NC 4.0},
}
RIS
TY - JOUR
TI - Melting from 1000°C and geophysical discontinuities in the shallow Earth’s mantle
AU - Emmanuel Gardés
AU - Mickael Laumonier
AU - Tahar Hammouda
AU - Geeth Manthilake
PY - 2026
DA - 2026/10/22
JO - Earth and Planetary Science Letters
DO - 10.1016/j.epsl.2026.120006
UR - https://hal.science/hal-05834917v1
AB - Numerous geophysical studies reported low seismic velocity and high electrical conductivity anomalies in the shallow, oceanic upper mantle of the Earth, at a level sometimes referred to as the Gutenberg discontinuity. This discontinuity is commonly interpreted to mark the onset of partial melting in the mantle, and also to correspond to the lithosphere-asthenosphere boundary (LAB), where the decoupling of the cold and rigid plates from the hot and convecting mantle drives plate tectonics. From petrological experiments and modelling, we determined the melting temperature of the mantle with relevant CO₂ and H₂O contents, which can be as low as ~1000°C. We evidence that Earth's mantle does start melting at pressures and temperatures corresponding to the Gutenberg discontinuity. However, this discontinuity is clearly located within the lithosphere, at about two thirds of its thickness, and thus does not represent the LAB. The low temperatures (down to ~1000°C) and the low fractions of melts at the Gutenberg discontinuity do not lower the viscosity of the mantle significantly. The LAB lies deeper at much higher temperatures (~1300-1400°C) where melting has progressed. This indicates it is not the onset of melting but the increase in melt fraction at the transition from volatile-to silicate-controlled melting that reduces mantle viscosity so as to drive plate tectonics at the LAB.
SN - 0012-821X
ER -