Mantle sulfide geobarometry

doi:10.1016/0016-7037(93)90563-C

Geochimica et Cosmochimica Acta

Volume 57, Issue 10, May 1993, Pages 2213-2222

https://doi.org/10.1016/0016-7037(93)90563-C Get rights and content

Abstract

A method of oxygen and sulfur barometry is based on the equilibrium, 2 Fe₂SiO₄ + S₂ = 2 FeS + Fe₂Si₂O₆ + O₂, as contained in the peridotite mineral assemblage olivine-orthopyroxene-MSS (monosulfide solid solution {Fe,Ni,Co,Cu} S-S₂). The method was applied to spinel peridotite xenoliths in basalts from the Massif Central and Montferrier and to the Ariege (Pyrenees) orogenic peridotite massifs. Monosulfide solid solution compositions were taken exclusively from sulfide inclusions within silicates and are interpreted to represent subsolidus MSS formed during high P-T recrystallization and deformation of the peridotites. Calculated $ƒ_{O_{2}}$ 's are consistent with spinel oxybarometry of shallow subcontinental mantle lithosphere but are more scattered. Scatter is due, at least in part, to nonrandom sectioning of multiphase sulfide grains. The $ƒ_{S_{2}}$ 's, which are coupled to $ƒ_{O_{2}}$ through the equilibrium above, average 1–2 log units above the quartz-fayalite-magnetite-pyrrhotite reference buffer. At such conditions, in primitive mantle containing 200–250 ppm S, at least 95% of that S would be present in MSS and 5% or less (as minor H₂S) in CO₂-H₂O fluids.

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Multi-stage sulfur and carbon mobility in fossil continental subduction zones: New insights from carbonate-bearing orogenic peridotites
2021, Geochimica et Cosmochimica Acta
Citation Excerpt :
Additionally, the overall lack of identifiable reduced carbon species (i.e. graphite or disordered carbonaceous material; e.g., Vitale Brovarone et al., 2020) in the UZ peridotites requires carbon to be present mostly as carbonate (CO2). We speculate that any S added from melt leaving a lithospheric mantle source would have involved an H2S-CO2-bearing agent, consistent with suggestions that mantle fluids are H2S-dominated (Eggler and Lorand, 1993). With the onset of the Variscan Orogeny, the corner flow initiated by continental subduction dragged the UZ peridotites deeper into the lithospheric mantle towards the slab-wedge interface, causing their textural transition from coarse protogranular to porphyroclastic and finally fine-grained equigranular.
The volatile transfer in subduction zones and the role of sulfate as a vector for the mobilization of oxidized components from down-going slabs remain hotly debated issues. Orogenic spinel and garnet peridotite lenses from the Ulten Zone (Eastern Alps, Italy), exhumed as part of felsic metamorphic terranes in continental collision zones, bear witness to mass transfer processes in these pivotal environments.
In this study, we carried out a multi-method investigation of mantle sulfides coexisting with four generations of carbonates, indicating coupled sulfur and carbon mobility throughout the peridotites’ metamorphic evolution as part of the Variscan subduction architecture. Detailed petrography, bulk rock measurements, in situ chemical and geochemical analyses of sulfides as well as Sr isotope analyses of associated clinopyroxene and amphibole are combined with the aim to constrain the origin, nature and effect of multiple C-O-H-S-bearing fluids and melts the peridotites interacted with. The first, pre-peak, metasomatic pulse (Stage 1) is represented by an H₂S-CO₂-bearing melt from the subduction-modified hot mantle wedge, which formed a pyroxenite layer hosting matrix pentlandite with δ³⁴S of +2.77‰. Matrix carbonates occasionally occur in the coarse-grained peridotite under eclogite-facies conditions (Stage 2), with heavier δ³⁴S (up to +3.43‰), radiogenic Sr (⁸⁷Sr/⁸⁶Sr_{clinopyroxene} > 0.7052) and elevated Pb abundances. These are ascribed to interaction with isotopically heavy melts carrying recycled crustal component, permissive of, but not requiring, involvement of oxidized S species. Conversely, isotopically lighter matrix pentlandite (δ³⁴S = −1.62 to +0.67‰), and radiogenic Sr in amphibole (⁸⁷Sr/⁸⁶Sr = 0.7056) and associated dolomite (published data) from fine-grained garnet-amphibole peridotites may point to involvement of H₂S-CO₂-bearing crustal fluids, which variably equilibrated with the mantle before interacting with the peridotites. The post-peak Stage 3 marks the entrapment of peridotites into a tectonic mélange. Here, kelyphitization of garnet is catalyzed by further ingress of a S-bearing fluid (δ³⁴S = −0.38‰), while carbonate veining with occasional sulfides bear witness to channelized fluid flow. Sulfide and amphibole grains in retrogressed spinel peridotites reveal the highest contents of fluid-mobile elements (As, Sb) and ⁸⁷Sr/⁸⁶Sr_amphibole up to 0.7074, suggesting late interactions with isotopically heavy crustal fluids at high fluid-rock ratios. Textural observations indicate that, during Stage 4, serpentinization of peridotites at low ƒS₂ played an active role not only in CO₂ release by conversion of dolomite to calcite + brucite intergrowths, but also in local removal of ³²S during the final exhumation stage. Late channelized sulfur remobilization is evidenced by the serpentine + magnetite (±millerite ± calcite) vein carrying > 300 ppm S.
Overall, the relatively narrow range of sulfur isotope composition (δ³⁴S = −1.62 to +3.76‰) is indicative of limited interaction with isotopically heavy crustal liquids, and points to a subordinate role of subduction-derived sulfate throughout the extended fluid(melt)/rock evolution of the Ulten Zone peridotites, first in the mantle wedge and then as part of a tectonic mélange.
Base metal sulphide geochemistry of southern African mantle eclogites (Roberts Victor): Implications for cratonic mafic magmatism and metallogenesis
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Platinum-group elements (PGE) display a chalcophile behaviour and are largely hosted by base metal sulphide (BMS) minerals in the mantle. During partial melting of the mantle, BMS release their metal budget into the magma generated. The fertility of magma sources is a key component of the mineralisation potential of large igneous provinces (LIP) and the origin of orthomagmatic sulphide deposits hosted in cratonic mafic magmatic systems. Fertility of mantle-derived magma is therefore predicated on our understanding of the abundance of metals, such as the PGE, in the asthenospheric and lithospheric mantle. Estimations of the abundance of chalcophile elements in the upper mantle are based on observations from mantle xenoliths and BMS inclusions in diamonds. Whilst previous assessments exist for the BMS composition and chalcophile element budget of peridotitic mantle, relatively few analyses have been published for eclogitic mantle. Here, we present sulphide petrography and an extensive in situ dataset of BMS trace element compositions from Roberts Victor eclogite xenoliths (Kaapvaal Craton, South Africa). The BMS are dominated by pyrite-chalcopyrite-pentlandite (± pyrrhotite) assemblages with S/Se ratios ranging 1200 to 36,840 (with 87% of analyses having S/Se <10,000. Total PGE abundance in BMS range from 0.17 to 223 ppm. We recognise four end-member compositions (types i to iv), distinguished by total PGE abundance and Pt/Pd and Au/Pd ratios. The majority of BMS have low PGE abundances (< 10 ppm) but Type iv BMS have the highest concentration of PGE recorded in eclogites so far (> 100 ppm) and are characteristically enriched in Os, Ir, Ru and Rh. Nano- and micron-scale Pd-Pt antimonide, telluride and arsenide platinum-group minerals (PGM) are observed spatially associated with BMS. We suggest that the predominance of pyrite in the xenoliths reflects the process of eclogitisation and that the trace element composition of the eclogite BMS was inherited from oceanic crustal protoliths of the eclogites, introduced into the SCLM via ancient subduction during formation of the Colesberg Magnetic Lineament c. 2.9 Ga and the cratonisation of the Kaapvaal Craton. Crucially, we demonstrate that the PGE budget of eclogitic SCLM may be substantially higher than previously reported, akin to peridotitic compositions, with significant implications for the PGE fertility of cratonic mafic magmatism and metallogenesis. We quantitatively assess these implications by modelling the chalcophile geochemistry of an eclogitic melt component in parental magmas of the mafic Rustenburg Layered Suite of the Bushveld Complex.
An effect of reduced S-rich fluids on diamond formation under mantle-slab interaction
2019, Lithos
Experimental study, dedicated to understanding the effect of S-rich reduced fluids on the diamond-forming processes under subduction settings, was performed using a multi-anvil high-pressure split-sphere apparatus in Fe₃C-(Mg,Ca)CO₃-S and Fe⁰-(Mg,Ca)CO₃-S systems at the pressure of 6.3 GPa, temperatures in the range of 900–1600 °C and run time of 18–60 h. At the temperatures of 900 and 1000 °C in the carbide-carbonate-sulfur system, extraction of carbon from cohenite through the interaction with S-rich reduced fluid, as well as C⁰-producing redox reactions of carbonate with carbide were realized. As a result, graphite formation in assemblage with magnesiowüstite, cohenite and pyrrhotite (±aragonite) was established. At higher temperatures (≥1100 °C) formation of assemblage of Fe³⁺-magnesiowüstite and graphite was accompanied by generation of fO₂-contrasting melts - metal-sulfide with dissolved carbon (Fe-S-C) and sulfide-oxide (Fe-S-O). In the temperature range of 1400–1600 °C spontaneous diamond nucleation was found to occur via redox interactions of carbide or iron with carbonate. It was established, that interactions of Fe-S-C and Fe-S-O melts as well as of Fe-S-C melt and magnesiowüstite, were С⁰-forming processes, accompanied by disproportionation of Fe. These resulted in the crystallization of Fe³⁺-magnesiowüstite+graphite assemblage and growth of diamond. We show that a participation of sulfur in subduction-related elemental carbon-forming processes results in sharp decrease of partial melting temperatures (~300 °C), reducting the reactivity of the Fe-S-C melt relatively to FeC melt with respect to graphite and diamond crystallization and decrease of diamond growth rate.
Experimental determination of carbon solubility in Fe-Ni-S melts
2018, Geochimica et Cosmochimica Acta
To investigate the effect of metal/sulfide and Ni/Fe ratio on the C storage capacity of sulfide melts, we determine carbon solubility in Fe-Ni-S melts with various (Fe + Ni)/S and Ni/Fe via graphite-saturated high-pressure experiments from 2–7 GPa and 1200–1600 °C. Consistent with previous results, C solubility is high (4–6 wt.%) in metal-rich sulfide melts and diminishes with increasing S content. Melts with near M/S = 1 (X_S > 0.4) have <0.5 wt.% C in equilibrium with graphite. C solubility is diminished modestly with increased Ni/Fe ratio, but the effect is most pronounced for S-poor melts, and becomes negligible in near-monosulfide compositions. Immiscibility between S-rich and C-rich melts is observed in Ni-poor compositions, but above ∼18 wt.% Ni there is complete miscibility. Because mantle sulfide compositions are expected to have high Ni concentrations, sulfide-carbide immiscibility is unlikely in natural mantle melts. An empirical parameterization of C solubility in Ni-Fe-S melts as a function of S and Ni contents allows estimation of the C storage capacity of sulfide in the mantle. Importantly, as the metal/sulfide (M/S) ratio of the melt increases, C storage increases both because C solubility increases and because the mass fraction of melt is enhanced by addition of metal from surrounding silicates. Under comparatively oxidized conditions where melts are near M/S = 1, as prevails at <250 km depth, bulk C storage is <3 ppm. In the deeper, more reduced mantle where M/S increases, up to 200 ppm C in typical mantle with 200 ± 100 ppm S can be stored in Fe-Ni-S melts. Thus, metal-rich sulfide melts are the principal host of carbon in the deep upper mantle and below. Residual carbon is present either as diamond or, if conditions are highly reduced and total C concentrations are low, solid alloy.
Origin and implications of troilite-orthopyroxene intergrowths in the brecciated diogenite Northwest Africa 7183
2018, Geochimica et Cosmochimica Acta
Citation Excerpt :
The oxygen fugacity during the post-magmatic Mg-Fe interdiffusion might not have been identical to that during the sulfidation reaction of olivine to orthopyroxene. If we take the oxygen fugacity (IW−2.5) at 2000 bars and 1000 °C of NWA 5480 (Peslier et al., 2015), which is an olivine-rich diogenite, and assume that the Fa content of olivine is 0.3, the sulfur fugacity logfS2 during sulfidation of olivine is approximately −7.9 based on the calibration reaction in Eggler and Lorand (1993). Troilite is a common accessory mineral in HED meteorites (McSween et al., 2011; Mittlefehldt, 2015).
Troilite-orthopyroxene intergrowths are present as a common material in the brecciated diogenite Northwest Africa (NWA) 7183. In this study, we report on the petrographic, mineralogical, and rare earth element abundances of the troilite-orthopyroxene intergrowths to constrain their origin and assess their implications for the diverse petrogenesis of diogenites.
Two groups of troilite-orthopyroxene intergrowths with various grain sizes and mineral chemistry have been observed in NWA 7183. One group of intergrowths contains fine-grained (<5 μm) olivine and chromite as inclusions in orthopyroxene (10–20 μm in size). The other group, in which orthopyroxene is more fine-grained (<10 μm in size), is closely associated with coarse irregular olivine grains. The orthopyroxene grains in both groups of troilite-orthopyroxene intergrowths are depleted in Cr, Al, Ti, and Ca compared with diogenitic orthopyroxene. Based on the texture and mineral chemistry, we suggest that the two groups of troilite-orthopyroxene intergrowths formed via reactions between diogenitic olivine and S-rich vapors, probably at different temperatures. The fact that some of the intergrowths are included in diogenitic lithic clasts indicates that the formation of the host diogenite should postdate the formation of the majority of troilite-orthopyroxene intergrowths. This relationship further implies that not all of the diogenites are cumulates that directly crystallized from the Vestan magma ocean. Instead, they probably originated from partial melting and recrystallization of magma ocean cumulates. The replacement of olivine by troilite and orthopyroxene intergrowths can partly explain why the expected olivine-rich lithologies were not detected at the two south pole impact basins on Vesta.
Iron carbide as a source of carbon for graphite and diamond formation under lithospheric mantle P-T parameters
2017, Lithos
Experimental modeling of natural carbide-involving reactions, implicated in the graphite and diamond formation and estimation of the iron carbide stability in the presence of S-bearing fluids, sulfide melts as well as mantle silicates and oxides, was performed using a multi-anvil high-pressure split-sphere apparatus. Experiments were carried out in the carbide-sulfur (Fe₃C-S), carbide-sulfur-oxide (Fe₃C-S-SiO₂-MgO) and carbide-sulfide (Fe₃C-FeS₂) systems, at pressure of 6.3 GPa, temperatures in the range of 900–1600 °C and run time of 18–40 h. During the interaction of cohenite with S-rich reduced fluid or pyrite at 900–1100 °C, extraction of carbon from carbide was realized, resulting in the formation of graphite in assemblage with pyrrhotite and cohenite. At higher temperatures complete reaction of cohenite with newly-formed sulfide melt was found to produce metal-sulfide melt with dissolved carbon (Fe₆₄S₂₇C₉ (1200 °C)–Fe₅₄S₄₀C₆ (1500 °C), at.%), which acted as a crystallization medium for graphite (1200–1600 °C) and diamond growth on seeds (1300–1600 °C). Reactions of cohenite and oxides with S-rich reduced fluid resulted in the formation of graphite in assemblage with highly ferrous orthopyroxene and pyrrhotite (900–1100 °C) or in hypersthene formation, as well as graphite crystallization and diamond growth on seeds in the Fe-S-C melt (1200–1600 °C). We show that the main processes of carbide interaction with S-rich fluid or sulfide melt are recrystallization of cohenite (900–1100 °C), extraction of carbon and iron in the sulfide melt, and graphite formation and diamond growth in the metal-sulfide melt with dissolved carbon. Our results evidence that iron carbide can act as carbon source in the processes of natural graphite and diamond formation under reduced mantle conditions. We experimentally demonstrate that cohenite in natural environments can be partially consumed in the reactions with mantle silicates and oxides, and is absolutely unstable in the presence of S-bearing reduced fluid or sulfide melt at temperatures higher than 1100 °C, under lithospheric mantle pressures.

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Mantle sulfide geobarometry

Abstract

Geochim. Cosmochim. Acta

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Intrinsic oxygen fugacity measurements: Techniques and results for spinels from upper mantle peridotites and megacryst assemblages

Geochim. Cosmochim. Acta

Oxygen fugacity controls in the Earth's upper mantle

Nature

High-pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen barometer: Implications for the oxidation state of the upper mantle

Contrib. Mineral. Petrol.

Compressibility; elastic constants

Distribution of trace transition elements in olivine and pyroxenes from ultramafic xenoliths

Amer. Mineral.

Petrographic Modal Analysis

Applications of olivine-orthopyroxene-spinel oxygen geobarometers to the redox state of the upper mantle

Sulfide phase equilibria

REE and Sr-Nd isotopic geochemistry of Eastern Pyrenean peridotite massifs: Paleozoic subcontinental lithosphere modified by subsequent magmatism?

Interpretation of the sulfide assemblages in a suite of xenoliths from Kilbourne Hole, New Mexico

GSA Spec. Paper

Upper mantle oxidation state: Evidence from olivine-orthopyroxene-ilmenite assemblages

Geophys. Res. Lett.

Petrology and thermal history of highly deformed mantle xenoliths from the Montferrer basanites, Languedoc, southern France: A comparison with ultramafic complexes from the North Pyrenean zone

J. Petrol.

Evidence for modal metasomatism in the orogenic-type spinel Iherzolite body from Caussou (Northeastern Pyrenees, France)

J. Petrol.