Hydrous Carbonatitic Liquids Drive CO2 Recycling From Subducted Marls and Limestones
Metadatos
Afficher la notice complèteEditorial
John Wiley & Sons
Date
2020-03-24Referencia bibliográfica
Schettino, E. and Poli, S. (2020). Hydrous Carbonatitic Liquids Drive CO2 Recycling From Subducted Marls and Limestones. In Carbon in Earth's Interior (eds C.E. Manning, J.-F. Lin and W.L. Mao). [https://doi.org/10.1002/9781119508229.ch18]
Patrocinador
Ministry of Education, Universities and Research (MIUR); Deep Carbon Observatory (DCO)Résumé
Pelagic limestones are subducted in a variety of subduction zones worldwide. Despite the geochemical relevance
of systems enriched in CaCO3, previous experimental investigations mostly focused on carbonated pelites, with
low Ca/(Ca+Mg+Fe) ratio. We present the compositions and the formation conditions of liquids in the model
system CaO‐Al2O3‐SiO2‐H2O‐CO2 (CASHC), building on phase relationships in the subsystems CHC and
CSHC, where a second critical endpoint was suggested at temperatures as low as 515 °C, and 3.2 GPa. Multianvil
experiments were performed at 4.2 and 6.0 GPa on five bulk compositions at variable Ca/Si/Al ratios. H2O
contents
vary from 5.6 to 21 wt%. Aragonite + kyanite + vapor and minor lawsonite form at 700 °C, replaced by
zoisite/grossular at 800 °C. Between 850 °C and 950 °C, a complex sequence of textural features is observed
upon quenching of a single volatile‐rich liquid phase formed at run conditions. Precipitates include dendritic
CaCO3, silicate glass, and Al‐rich whiskers. The bulk composition of such hydrous carbonatitic liquids is
retrieved by image analysis on X‐ray maps, showing Ca/Si ratio increasing with pressure and temperature.
Hydrous Ca‐carbonatitic liquids are efficient media for scavenging volatiles from subducted crustal material and
for metasomatizing the mantle wedge.