Universität zu Köln

Martirosyan, Naira S., Efthimiopoulos, Ilias, Pennacchioni, Lea, Wirth, Richard, Jahn, Sandro ORCID: 0000-0002-2137-8833 and Koch-Mueller, Monika (2021). Effect of cationic substitution on the pressure-induced phase transitions in calcium carbonate. Am. Miner., 106 (4). S. 549 - 559. CHANTILLY: MINERALOGICAL SOC AMER. ISSN 1945-3027

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Abstract

The high-pressure CaCO3 phase diagram has been the most extensively studied within the carbonates group. However, both the diverse mineralogy of carbonates and the abundance of solid solutions in natural samples require the investigation of multi-component systems at high pressures (P) and temperatures (T). Here we studied a member of the CaCO3-SrCO3 solid-solution series and revealed the effect of cationic substitution on the pressure-induced phase transitions in calcium carbonate. A synthetic solid solution Ca0.82Sr0.18CO3 was studied in situ by Raman spectroscopy in a diamond-anvil cell (DAC) up to 55 GPa and 800 K. The results of this work show significant differences in the high-pressure structural and vibrational behavior of the (Ca,Sr)CO3 solid solution compared to that of pure CaCO3. The monoclinic CaCO3-II-type structure (Sr-calcite-II) was observed already at ambient conditions instead of the expected rhombohedral calcite. The stress-induced phase transition to a new high-pressure modification, termed here as Sr-calcite-IIIc, was detected at 7 GPa. Sr-calcite-VII formed already at 16 GPa and room T, which is 14 GPa lower compared to CaCO3-VII. Finally, crystallization of Sr-aragonite was detected at 540 K and 9 GPa, at 200 K lower T than pure aragonite. Our results indicate that substitution of Ca2+ by bigger cations, such as Sr2+, in CaCO3 structures can stabilize phases with larger cation coordination sites (e.g., aragonite, CaCO3-VII, and post-aragonite) at lower P-T conditions compared to pure CaCO3. The present study shows that the role of cationic composition in the phase behavior of carbonates at high pressures should be carefully considered when modeling the deep carbon cycle and mantle processes involving carbonates, such as metasomatism, deep mantle melting, and diamond formation.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Martirosyan, Naira S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Efthimiopoulos, Ilias UNSPECIFIED UNSPECIFIED UNSPECIFIED Pennacchioni, Lea UNSPECIFIED UNSPECIFIED UNSPECIFIED Wirth, Richard UNSPECIFIED UNSPECIFIED UNSPECIFIED Jahn, Sandro UNSPECIFIED orcid.org/0000-0002-2137-8833 UNSPECIFIED Koch-Mueller, Monika UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-583617
DOI:	10.2138/am-2021-7547
Journal or Publication Title:	Am. Miner.
Volume:	106
Number:	4
Page Range:	S. 549 - 559
Date:	2021
Publisher:	MINERALOGICAL SOC AMER
Place of Publication:	CHANTILLY
ISSN:	1945-3027
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language CRYSTAL-STRUCTURE; HIGH-TEMPERATURE; DIAMOND; INCLUSIONS; CACO3; GPA; SPECTROSCOPY; CACO3-MGCO3; POLYMORPHS; BEHAVIOR Multiple languages Geochemistry & Geophysics; Mineralogy Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/58361