Formation Conditions of Unusual Extremely Reduced High-Temperature Mineral Assemblages in Rocks of Combustion Metamorphic Complexes DOI Creative Commons
I. S. Peretyazhko, Е. A. Savina

Crystals, Journal Year: 2024, Volume and Issue: 14(12), P. 1052 - 1052

Published: Dec. 3, 2024

New data, including Raman spectroscopy, characterize unusual mineral assemblages from rocks of the Naylga and Khamaryn–Khyral–Khiid combustion metamorphic complexes in Mongolia. Several samples melilite–nepheline paralava other thermally altered (metamorphosed) sedimentary contain troilite (FeS), metallic iron Fe0, kamacite α-(Fe,Ni) or Ni-bearing taenite γ-(Fe,Ni) Ni-rich barringerite allabogdanite Fe2P, schreibersite Fe3P, steadite Fe4P = eutectic α-Fe + wüstite FeO, cohenite Fe3C. The matrix includes a fragment composed magnesiowüstite–ferropericlase (FeO–MgO solid solution), as well spinel (Mg,Fe)Al2O4 forsterite. highest-temperature assemblage belongs to xenolithic remnant, possibly Fe-rich sinter, which is molten ash left after underground coal seams. crystallization temperatures observed phases were estimated using phase diagrams for respective systems: Fe–S sulfides Fe–P ± C phosphides. Iron monosulfides (high-temperature pyrrhotite) with inclusions Fe0 underwent solid-state conversion into at 140 °C. phosphides early growth zone anorthite–bytownite crystallized <1370 1165 °C (Fe2P), 1165–1048 (Fe3P), <1048 (Fe4P). Phase relations zoned spherules consisting +Fe0 (or taenite) +Fe3P (Fe3C, Fe4P) reveal potential presence homogeneous Fe–S–P–C melt T~1350 °C, separated two immiscible melts 1350–1250 range; namely, dense Fe–P–C core less rim. evolved accordance cooling paths diagrams. Cohenite between 988 959 minerals used reconstruct redox patterns respect CCO, IW, IM, MW buffer equilibria during melting marly limestone subsequent melts. origin studied CM was explained model implying thermal alteration low-permeable overburden domains reducing conditions wild subsurface fires, while heating transferred conductively adjacent parts ignited fluid (gas) regime zones controlled by CCO excess atomic carbon. Paralava exposed high-temperature extremely contained droplets Fe–S–P–C, Fe–S, Fe–P, melts, then reduced assemblages.

Language: Английский

Iron-based eutectics, a valuable geological record DOI
Oleg S. Vereshchagin, Vladimir V. Shilovskikh, Л. В. Камаева

et al.

Lithos, Journal Year: 2025, Volume and Issue: unknown, P. 108057 - 108057

Published: March 1, 2025

Language: Английский

Citations

0
Formation Conditions of Unusual Extremely Reduced High-Temperature Mineral Assemblages in Rocks of Combustion Metamorphic Complexes DOI Creative Commons
I. S. Peretyazhko, Е. A. Savina

Crystals, Journal Year: 2024, Volume and Issue: 14(12), P. 1052 - 1052

Published: Dec. 3, 2024

New data, including Raman spectroscopy, characterize unusual mineral assemblages from rocks of the Naylga and Khamaryn–Khyral–Khiid combustion metamorphic complexes in Mongolia. Several samples melilite–nepheline paralava other thermally altered (metamorphosed) sedimentary contain troilite (FeS), metallic iron Fe0, kamacite α-(Fe,Ni) or Ni-bearing taenite γ-(Fe,Ni) Ni-rich barringerite allabogdanite Fe2P, schreibersite Fe3P, steadite Fe4P = eutectic α-Fe + wüstite FeO, cohenite Fe3C. The matrix includes a fragment composed magnesiowüstite–ferropericlase (FeO–MgO solid solution), as well spinel (Mg,Fe)Al2O4 forsterite. highest-temperature assemblage belongs to xenolithic remnant, possibly Fe-rich sinter, which is molten ash left after underground coal seams. crystallization temperatures observed phases were estimated using phase diagrams for respective systems: Fe–S sulfides Fe–P ± C phosphides. Iron monosulfides (high-temperature pyrrhotite) with inclusions Fe0 underwent solid-state conversion into at 140 °C. phosphides early growth zone anorthite–bytownite crystallized <1370 1165 °C (Fe2P), 1165–1048 (Fe3P), <1048 (Fe4P). Phase relations zoned spherules consisting +Fe0 (or taenite) +Fe3P (Fe3C, Fe4P) reveal potential presence homogeneous Fe–S–P–C melt T~1350 °C, separated two immiscible melts 1350–1250 range; namely, dense Fe–P–C core less rim. evolved accordance cooling paths diagrams. Cohenite between 988 959 minerals used reconstruct redox patterns respect CCO, IW, IM, MW buffer equilibria during melting marly limestone subsequent melts. origin studied CM was explained model implying thermal alteration low-permeable overburden domains reducing conditions wild subsurface fires, while heating transferred conductively adjacent parts ignited fluid (gas) regime zones controlled by CCO excess atomic carbon. Paralava exposed high-temperature extremely contained droplets Fe–S–P–C, Fe–S, Fe–P, melts, then reduced assemblages.

Language: Английский

Citations

1