Polymerized 4-Fold Coordinated Carbonate Melts in the Deep Mantle

• Published in: Frontiers in earth science (Lausanne) Vol. 7
• Main Authors: Sanloup, Chrystèle, Hudspeth, Jessica M., Afonina, Veronika, Cochain, Benjamin, Konôpková, Zuzana, Lelong, Gérald, Cormier, Laurent, Cavallari, Chiara
• Format: Journal Article
• Language: English
• Published: Frontiers Media 10-04-2019; Frontiers Media S.A
• Subjects: carbonate melts; Earth Sciences; high pressure; polymerization; Raman; Sciences of the Universe; x-ray diffraction; x-ray Raman; X-ray Raman; polymerization; deep mantle; carbonate melts; x-ray diffraction; Raman; high pressure
• ISSN: 2296-6463; 2296-6463
• DOI: 10.3389/feart.2019.00072

Our understanding of the deep carbon cycle has witnessed amazing advances in the last decade, including the discovery of tetrahedrally coordinated high pressure (P) carbonate phases. However, little is known about the physical properties of their molten counterpart at moderate depths, while their properties at lower mantle conditions remain unexplored. Here, we report the structure and density of FeCO3 melts and glasses from 44 to 110 GPa by means of in situ x-ray synchrotron diffraction, and ex situ Raman and x-ray Raman spectroscopies. Carbon is fully transformed to 4-fold coordination, a bond change recoverable at ambient P. While low P melts react with silica, resulting in the formation of silico-carbonate glasses, high P melts are not contaminated but still quench as glasses. Carbonate melts are therefore polymerized, highly viscous and poorly reacting with silicates in the lower mantle, in stark opposition with their low P properties.