Immiscible metallic melts in the upper mantle beneath Mount Carmel, Israel: Silicides, phosphides, and carbides

Abstract

Xenolithic corundum aggregates in Cretaceous mafic pyroclastics from Mount Carmel contain pockets of silicate melts with mineral assemblages (SiC (moissanite), TiC, Ti 2 O 3 (tistarite), Fe-Ti-Zr silicides/phosphides) indicative of magmatic temperatures and oxygen fugacity (fO 2 ) at least 6 log units below the Iron-Wüstite buffer (IW≤-6). Microstructural evidence indicates that immiscible, carbon-rich metallic (Fe-Ti-Zr-Si-P) melts separated during the crystallization of the silicate melts. The further evolution of these metallic melts was driven by the crystallization of two main ternary phases (FeTiSi and FeTiSi 2 ) and several near-binary phases, as well as the separation of more evolved immiscible melts.Reconstructed melt compositions fall close to cotectic curves in the Fe-Ti-Si system, consistent with trapping as metallic liquids. Temperatures estimated from comparisons with experimental work range from ≥1500 °C to ca 1150 °C; these probably are maximum values, due to the solution of C, H, P and Zr. With decreasing temperature (T), the Si, Fe and P contents of the Fe-Ti-Si melts increased, while contents of Ti and C decreased. The increase in Si with declining T implies a corresponding decrease in fO 2 , probably to ca IW-9. The solubility of P in the metallic melts declined with T and fO 2 , leading to immiscibility between Fe-Ti-Si melts and (Ti,Zr)-(P,Si) melts. Decreasing T and fO 2 also reduced the solubility of C in the liquid metal, driving the continuous crystallization of TiC and SiC during cooling. The lower-T metallic melts are richer in Cr, and to some extent V, as predicted by experimental studies showing that Cr and V become more siderophile with decreasing fO 2 .These observations emphasise the importance of melt-melt immiscibility for the evolution of magmas under reducing conditions. The low fO 2 and the abundance of carbon This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

Evidence of the anthropogenic origin of the ‘Carmel sapphire’ with enigmatic super-reduced minerals

“…2O7 (Ma et al, 2021); ziroite (IMA2022-013) ZrO2 ; sassite (IMA2022-014) Ti 3+ 2Ti 4+ O5 ; mizraite-(Ce) (IMA2022-027) Ce(Al11Mg)O19 ; toledoite (IMA2022-036) TiFeSi ; and yeite (IMA2022-079) TiSi . Grain aggregates of CS (and also hibonite and moissanite) from Carmel have been the objects of numerous scientific publications (Griffin et al, 2016(Griffin et al, , 2018(Griffin et al, -2022Xiong et al, 2017; https://doi.org/10.1180/mgm.2023.25 Published online by Cambridge University Press Dobrzhinetskaya et al, 2018;Cámara et al, 2019;Bindi et al, 2019Bindi et al, , 2020Huang et al, 2020;Stan et al, 2020;Oliveira et al, 2021;Lu et al, 2022), in which the authors present the highly controversial hypothesis that the corundum rock with SR minerals formed at the crust-mantle boundary as a result of CH4+H2 fluid flowing through the magmatic melt.…”

“…This corundum with inclusions of super-reduced minerals obtained the trademark ‘Carmel sapphire’ and has been the host of 10 new mineral species discovered in the last five years and approved by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA): carmeltazite (IMA2018-103) ZrAl 2 Ti 4 O 11 (Griffin et al , 2018); kishonite (IMA2020-023) VH 2 (Bindi et al , 2020); oreillyite (IMA 2020-030a) Cr 2 N (Bindi et al , 2020); griffinite (IMA 2021-110) Al 2 TiO 5 (Ma et al , 2022a); magnéliite (IMA2021-111) Ti 3+ 2 Ti 4+ 2 O 7 (Ma et al , 2022b); ziroite (IMA2022-013) ZrO 2 (Ma et al , 2022c); sassite (IMA2022-014) Ti 3+ 2 Ti 4+ O 5 (Ma et al , 2022d); mizraite-(Ce) (IMA2022-027) Ce(Al 11 Mg)O 19 (Ma et al , 2022e); toledoite (IMA2022-036) TiFeSi (Ma et al , 2022f); and yeite (IMA2022-079) TiSi (Ma et al , 2023). Grain aggregates of Carmel sapphire (and also hibonite and moissanite) from Carmel have been the objects of numerous scientific publications (Griffin et al , 2016a,b, 2018, 2019a,b, 2020a,b, 2021a,b, 2022; Xiong et al , 2017; Dobrzhinetskaya et al , 2018; Cámara et al , 2019; Bindi et al , 2019, 2020; Huang et al , 2020; Stan et al , 2020; Oliveira et al , 2021; Lu et al , 2022), in which the authors present the highly controversial hypothesis that the corundum rock with super-reduced minerals formed at the crust–mantle boundary as a result of CH 4 +H 2 fluid flowing through the magmatic melt.…”

Discussion of the paper by Galuskin and Galuskina (2003), “Evidence of the anthropogenic origin of the ‘Carmel sapphire’ with enigmatic super-reduced minerals”

“…"skeletal osbornite occurring as inclusions in corundum". The illustrated nitrides are not 'skeletal crystals'they may appear to be so because they are controlled by crystallographically controlled void spaces in skeletal corundum (Griffin et al, 2016;2021a, 2022Oliveira et al, 2021). These spectacular structures are only one form of TiN in the Carmel sapphire; it also occurs in large inclusions coexisting with Fe-Ti silicides and TiB 2 , and as regular crystals that appear to have crystallised directly from Fe-Ti silicide melts (Griffin et al, 2020a(Griffin et al, , 2021a(Griffin et al, , 2022.…”

Wodegongjieite, ideally KCa3(Al7Si9)O32, a new sheet silicate isostructural with the feldspar polymorph kokchetavite, KAlSi3O8

“…Our current scenario for the formation of the 6 new minerals occurring in and around the spheroid of intermetallic phases in foil #5358 is based on the model developed by Griffin et al (2018Griffin et al ( , 2022 and Xiong et al (2017) for similar intermetallic phases at Mount Carmel, Israel.…”

“…Our current scenario for the formation of the six new minerals occurring in and around the spheroid of intermetallic phases in foil #5358 is based on the model developed by Griffin et al (2018Griffin et al ( , 2022 and Xiong et al (2017) for similar intermetallic phases at Mount Carmel, Israel. Mantle-derived CH 4 + H 2 fluids are believed to have interacted with basaltic magmas in the shallow lithosphere (depths of ∼30-100 km), which resulted in precipitation of corundum that entrapped intermetallic melts derived from the desilication of a parental magma, presumably basaltic.…”