Tetrahedrally coordinated carbonates in Earth’s lower mantle

Eglantine Boulard (1, 2) , Ding Pan (3) , Giulia Galli (3) , Zhenxian Liu (4) , Wendy L Mao (2, 5)

1 NEEL - MRS - Matériaux, Rayonnements, Structure
2 GS - Department of Geological Sciences [Stanford]
3 Institute for Molecular Engineering
4 Geophysical Laboratory [Carnegie Institution]
5 SLAC - SLAC National Accelerator Laboratory

Carbonates are the main species that bring carbon deep into our planet through subduction. They are an important rock-forming mineral group, fundamentally distinct from silicates in Earth's crust in that carbon binds to three oxygen atoms, while silicon is bonded to four oxygens. Here, we present experimental evidence that under the sufficiently high pressures and high temperatures existing in the lower mantle, ferromagnesian carbonates transform to a phase with tetrahedrally coordinated carbons. Above 80 GPa, in situ synchrotron infrared experiments show the unequivocal spectroscopic signature of the high-pressure phase of (Mg,Fe)CO 3. Using ab-initio calculations, we assign the new IR signature to CO bands associated with tetrahedrally coordinated carbon with asymmetric CO bonds. Tetrahedrally coordinated carbonates are expected to exhibit substantially

Domaines: Géophysique [physics.geo-ph]

Eglantine Boulard, Ding Pan, Giulia Galli, Zhenxian Liu, Wendy L Mao. Tetrahedrally coordinated carbonates in Earth’s lower mantle. Nature Communications, 2015, 6, pp.6311. ⟨10.1038/ncomms7311⟩. ⟨hal-01734781⟩