SEG Special Publications, Chapter 9: Anhydrite assimilation by ultramafic melts of the Bushveld Complex, and its consequences to petrology and mineralization

Anhydrite assimilation by ultramafic melts of the Bushveld Complex, and its consequences to petrology and mineralization

Yudovskaya, M.A., Sluzhenikin, S.F., Costin, G., Shatagin, K.N., Dubinina, E.O., Grobler, D.F., Ueckermann, H., and Kinnaird1, J.A.

in “Metals, Minerals and Society”, Special Publication no. 21, Society of Economic Geologists, Chapter 9,  pp. 177-206

Abstract

Sulfate assimilation by mafic to ultramafic melt is thought to be an important process in the genesis of magmatic PGE-Ni-Cu deposits. We consider petrological indicators and possible mechanisms of anhydrite assimilation by ultramafic melts of the northern limb of the Bushveld Complex. On farm Turfspruit, an anhydrite-bearing sedimentary raft of the Duitschland Formation separates the Platreef from underlying Lower zone peridotites. The proportion of anhydrite across the raft increases from negligible in corundum-sillimanite-magnetite hornfels at the base to 95 to 100% in anhydrite marble at the top. Underlying Lower zone peridotites lack anhydrite, whereas overlying Platreef pyroxenites contain both widespread interstitial to euhedral anhydrite as well as spherical to irregularly shaped anhydrite inclusions in association with olivine chadacrysts inside oikocrystic orthopyroxene. Olivine chadacryst compositions (Mg# 79–81 and 0.33–0.46 wt % NiO) support their pristine liquidus origin, although an association of Al-enriched orthopyroxene and interstitial anorthite indicates exchange reactions involving anhydrite and aluminosilicates from hornfels. Plagioclase from the anhydrite-contaminated rocks has an Sr isotope initial ratio (Sri) of 0.7047 to 0.7063, similar to the compositions of Bushveld early primitive magmas, in agreement with a relatively non-radiogenic signature of the anhydrite-bearing contaminant with Sri of 0.7057 to 0.7094. The range of Sri of plagioclase from the underlying Lower zone peridotites (0.7040– 0.7067) and from the Turfspruit platinum reefs just below the Main zone contact (0.7068–0.7084) supports their correlation and synchronous emplacement with the Lower zone and the top of the Upper Critical zone in the western and eastern limbs of the Bushveld. The δ34S values of anhydrite (12.2–14.5‰) and a coexisting pyrrhotite-millerite-chalcopyrite sulfide assemblage (6.2–7.8‰) in a hornfelsed raft and overlying pyroxenites are interpreted to have resulted from open system isotopic exchange, indicating closure temperatures of 750° to 820°C. The assimilation of sedimentary anhydrite is interpreted to be an important component of contact-style mineralization of the Platreef at Turfspruit that took place through the erosion and disintegration of footwall rocks by dynamic pulses of hot magmas. Chemical dissolution, thermal decomposition, and melting of sulfate-bearing rafts or xenoliths are viable assimilation processes that result in the saturation of silicate melt with sulfate, exsolution of immiscible sulfate melts, crystallization of cumulus and interstitial anhydrite, and precipitation of contact-style sulfide mineralization at the base of the intrusion. Reef-style mineralization at the top of the Platreef shows contrastingly negligible compositional and isotopic evidence of sulfate assimilation.

Yudovskaya, M.A., Sluzhenikin, S.F., Costin, G., Shatagin, K.N., Dubinina, E.O., Grobler, D.F., Ueckermann, H., and Kinnaird1, J.A. (2018): Anhydrite assimilation by ultramafic melts of the Bushveld Complex, and its consequences to petrology and mineralization. In “Metals, Minerals and Society”, Editors Antonio M. Arribas and Jeffrey L. Mauk. SEG Special publications no. 21, pp. 177-206.

https://www.segweb.org/store_info/SP/SP-21-Additional-Product-Info.pdf

JPet: Sulfur inventory of ocean island basalt source regions constrained by modeling the fate of sulfide during decompression melting of a heterogeneous mantle

Ding, S. and Dasgupta, R.

Abstract: The sulfur (S) and copper (Cu) contents of primitive mid-ocean ridge basalts (MORB) and ocean island basalts (OIB) are similar, although the latter are thought to be derived from hotter mantle. To reconcile the sulfur and chalcophile element budgets of OIB, we developed a model to describe the behavior of sulfide and Cu during decompression melting of mantle by combining experimental constraints on decompression melting at different excess mantle potential temperatures, TP, between 1400 and 1650°C, and empirical sulfur content at sulfide saturation (SCSS) models, which take into account the effect of Ni and Cu present in the equilibrium sulfide melt. Model calculations at TP = 1450–1650°C were applied to explain the S and Cu inventory of high-Mg# ‘reference’ OIB. Modeling indicates that partial melts relevant to OIB generation have higher SCSS than those of primitive MORB, because of the positive effect of temperature on SCSS. Therefore, for a given abundance of sulfide in the mantle, hotter mantle consumes sulfide more efficiently than colder mantle. Calculation of SCSS along melting adiabats at TP = 1450–1550°C, with variable initial S content of peridotite, indicates that sulfide-undersaturated primitive Icelandic basalts with ∼720 ppm S and 74–115 ppm Cu can be generated by 10–25 wt % melting of peridotite containing 100–150 ppm S. The S and Cu budgets of OIB that are thought to represent low-degree melts can be satisfied by (1) peridotite partial melting if a sulfide-saturated partial melt with a Ni content in the sulfide melt ≥25–30 wt % is derived from relatively cold mantle (TP ≤ 1450°C), or (2) if primitive melts parental to OIB are enriched in S (>1500 ppm), or (3) an extremely low (≤1%) degree of melting is applicable. Alternatively, if the Ni content in the equilibrium sulfide in the peridotitic mantle is ≤20–25 wt %, mixing of partial melts, derived from low-degree melting of MORB-eclogite and metapelite, with S-depleted peridotite partial melts may be necessary to reconcile the measured S and Cu contents in the low-F (<10%, where F is melt fraction) basalts from Galapagos spreading center, Lau Basin and Loihi for TP of 1450–1650°C. In this last case, sulfides, equivalent to 50–100 ppm S in the peridotite mantle, can be exhausted by 1–9 wt % partial melting. The total S inventory of the heterogeneous mantle source of these basalts is higher because of the presence of subducted eclogite ± sediments. Our analysis also suggests that compared with peridotite, which is likely to become sulfide-free during partial melting owing to the high SCSS for its partial melts, subducted MORB-eclogite and metapelite probably play important roles in retaining sulfide in the Earth’s shallow mantle, owing to low SCSS in their partial melts and high initial sulfide abundances.

 

Ding, S. & Dasgupta, R. (2018). Sulfur inventory of ocean island basalt source regions constrained by modeling the fate of sulfide during decompression melting of a heterogeneous mantle. Journal of Petrology 59, 1281–1308. doi:10.1093/petrology/egy061

Geochemical Perspectives Letters: Redox state of the convective mantle from CO2-trace element systematics of oceanic basalts

Redox state of the convective mantle from CO2-trace element systematics of oceanic basalts

By: James Eguchi, Rajdeep Dasgupta

Abstract: The redox state of mantle lithologies, based on xenoliths from continental lithospheric mantle, has been shown to decrease with depth and reach oxygen fugacities (fO2) at which graphite/diamond will be the stable form of carbon at pressures greater than about 3-4 GPa (e.g., Frost and McCammon, 2008). On the other hand, the depth-fO2 profile of the convecting mantle remains poorly known. We compare the CO-Ba and CO2-Nb systematics of natural oceanic basalts to the CO2-trace element concentrations that can be generated via contributions from depleted peridotite partial melts and graphite-saturated partial melts of subducted lithologies. Results suggest that to produce the CO2enrichments relative to the depleted end member observed in natural oceanic basalts, subducted lithologies cannot be graphite-saturated at the onset of melting or must undergo oxidative transformation below the respective volatile-free solidi. Therefore, the oxygen fugacity profile of the continental lithospheric mantle may not be applicable to the deep convecting upper mantle, with the convecting upper mantle to at least 150 km depth being more oxidised than the carbonate vs.graphite/diamond buffer.

 

 

Chemistry of Materials: A non-van der Waals 2D Material from natural titanium mineral ore Ilmenite

A non-van der Waals 2D Material from natural titanium mineral ore Ilmenite

Puthirath Balan, A., Radhakrishnan, S., Kumar, R., Neupane, R., Sinha, S.K., Deng, L., de los Reyes, C.A., Apte, A., Rao, B.M., Paulose, M., Vajtai, R., Chu, C.W., Costin, G., Marti, A.A., Varghese, O.K., Singh, A.K., Tiwary, C.S., Anantharaman, M.R., Ajayan, P.M

Chemistry of Materials  https://pubs.acs.org/doi/10.1021/acs.chemmater.8b01935

Abstract

Two dimensional (2D) materials from naturally occurring minerals are promising and possess interesting physical properties. A new 2D material ‘Ilmenene’ has been exfoliated from the naturally occurring titanate ore ilmenite (FeTiO3) by employing liquid phase exfoliation in dimethylformamide (DMF) solvent by ultrasonic bath sonication. Ilmenene displays [001] orientation which is confirmed by transmission electron microscopy (TEM). Probable charge transfer excitation from Fe2+Ti4+ to Fe3+Ti3+ results in ferromagnetic (FM) ordering along with the antiferromagnetic (AFM) phase accompanied by enhanced anisotropy due to surface spins. The 2D nature and bandgap states help ilmenene form a heterojunction photocatalyst with titania nanotube arrays, capable of broad spectrum light harvesting and separating/transferring the photo-generated charges effectively for solar photoelectrochemical water splitting.

Puthirath Balan, A., Radhakrishnan, S., Kumar, R., Neupane, R., Sinha, S.K., Deng, L., de los Reyes, C.A., Apte, A., Rao, B.M., Paulose, M., Vajtai, R., Chu, C.W., Costin, G., Marti, A.A., Varghese, O.K., Singh, A.K., Tiwary, C.S., Anantharaman, M.R., Ajayan, P.M., 2018. A non-van der Waals 2D Material from natural titanium mineral ore Ilmenite. Chem. Mater. acs.chemmater.8b01935. https://doi.org/10.1021/acs.chemmater.8b01935

https://pubs.acs.org/doi/10.1021/acs.chemmater.8b01935

 

Chemistry of Materials: Impurity controlled crystal growth in low dimensional bismuth telluride

Impurity controlled crystal growth in low dimensional bismuth telluride

Sharifi, T., Yazdi, S., Costin, G., Apte, A., Coulter, G., Tiwary, C., and Ajayan, P.M.

Chemistry of Materials,  https://pubs.acs.org/doi/10.1021/acs.chemmater.8b02548

ABSTRACT

Topological insulators, such as layered Bi2Te3, exhibit extraordinary properties, manifesting profoundly only
at nanoscale thicknesses. However, it has been challenging to synthesize these structures with controlled thickness. Here,
control over the thickness of solvothermally grown Bi2Te3 nanosheets is demonstrated by manipulating the crystal growth
through selected and controlled impurity atom addition. By a comprehensive analysis of growth mechanism and the intentional
addition of Fe impurity, it is demonstrated that the nucleation and growth of few-layer nanosheets of Bi2Te3 can be
stabilized in solution. By optimizing the Fe concentration, nanosheets thinner than 6 nm, and as thin as 2 nm, can be
synthesized. Such thicknesses are smaller than the anticipated critical thickness for the transition of topological
insulators to the quantum spin Hall regime.

 

Sharifi, T., Yazdi, S., Costin, G., Apte, A., Coulter, G., Tiwary, C., and Ajayan, P.M. (2018). Impurity controlled crystal growth in low dimensional bismuth telluride. Chemistry of Materials, p. acs.chemmater.8b02548. doi: 10.1021/acs.chemmater.8b02548

https://pubs.acs.org/doi/10.1021/acs.chemmater.8b02548

RCMS: Scale distortion from pressure baselines as a source of inaccuracy in triple-isotope measurements

Laurence Y. Yeung, Justin A. Hayles, Huanting Hu, Jeanine L. Ash, and Tao Sun

Rapid Comm. Mass Spectrom. (2018)

doi: 10.1002/rcm.8247

Rationale: Isotope ratio measurements have become extremely precise in recent years, with many approaching parts‐per‐million (ppm) levels of precision. However, seemingly innocuous errors in signal baselines, which exist only when gas enters the instrument, might lead to significant errors. These “pressure‐baseline” (PBL) offsets may have a variety of origins, such as incoherent scattering of the analyte, isobaric interferences, or electron ablation from the walls of the flight tube. They are likely present in all but ultra‐high‐resolution instruments, but their importance for high‐precision measurements has not been investigated.

Methods: We derive the governing equations for the PBL effect. We compare the oxygen triple‐isotope composition of gases on three different mass spectrometers before and after applying a correction for PBLs to determine their effects. We also compare the composition of atmospheric O2 with that of several standard minerals (San‐Carlos Olivine and UWG‐2) on two high‐precision mass spectrometers and compare those results with the differences reported in the literature.

Results: We find that PBLs lead to stretching or compression of isotopic variations. The scale distortion is non‐mass‐dependent, affecting the accuracy of triple‐isotope covariations. The governing equations suggest that linear stretching corrections using traditional isotopic delta values (e.g., δ18O) are rigorous for PBL‐induced errors in pure gases. When the reference and sample gases are not comparable in composition or purity, however, a different correction scheme may be required. These non‐mass‐dependent errors are systematic and may have influenced previous measurements of triple‐isotope covariations in natural materials.

Conclusions: Accurate measurements of isotopic variations are essential to biogeochemistry and for testing theoretical models of isotope effects. PBLs are probably ubiquitous, contributing to the interlaboratory disagreements in triple‐isotope compositions of materials differing greatly in δ18O values. Moreover, they may lead to inaccurate determination of triple‐isotope compositions and fractionation factors, which has implications for isotopic studies in hydrology and biogeochemistry.

GCA: Core-mantle fractionation of carbon in Earth and Mars: The effects of sulfur

Tsuno, K., Grewal, D.S., Dasgupta, R. (2018). Core-mantle fractionation of carbon in Earth and Mars: The effects of sulfur. Geochimica et Cosmochimica Acta 238: 477-495.

 

Abstract: Constraining carbon (C) fractionation between silicate magma ocean (MO) and core-forming alloy liquid during early differentiation is essential to understand the origin and early distribution of C between reservoirs such as the crust-atmosphere,
mantle, and core of Earth and other terrestrial planets. Yet experimental data at high pressure (P)-temperature (T) on the
effect of other light elements such as sulfur (S) in alloy liquid on alloy-silicate partitioning of C and C solubility in
Fe-alloy compositions relevant for core formation is lacking. Here we have performed multi-anvil experiments at
6–13 GPa and 1800–2000 °C to examine the effects of S and Ni on the solubility limit of C in Fe-rich alloy liquid as well
as partitioning behavior of C between alloy liquid and silicate melt (Dc). The results show that C solubility in the alloy
liquid as well as Dc decreases with increasing in S content in the alloy liquid. Empirical regression on C solubility in
alloy liquid using our new experimental data and previous experiments demonstrates that C solubility significantly increases
with increasing temperature, whereas unlike in S-poor or S-free alloy compositions, there is no discernible effect of Ni on C
solubility in S-rich alloy liquid.
Our modelling results confirm previous findings that in order to satisfy the C budget of BSE, the bulk Earth C undergoing
alloy-silicate fractionation needs to be as high as those of CI-type carbonaceous chondrite, i.e., not leaving any room for
volatility-induced loss of carbon during accretion. For Mars, on the other hand, an average single-stage core formation at
relatively oxidized conditions (1.0 log unit below IW buffer) with 10–16 wt% S in the core could yield a Martian mantle with
a C budget similar to that of Earth’s BSE for a bulk C content of 0.25–0.9 wt%. For the scenario where C was delivered to
the proto-Earth by a S-rich differentiated impactor at a later stage, our model calculations predict that bulk C content in the
impactor can be as low as ~0.5 wt% for an impactor mass that lies between 9 and 20% of present day Earth’s mass. This value
is much higher than 0.05–0.1 wt% bulk C in the impactor predicted by Li et al. (Li Y., Dasgupta R., Tsuno K., Monteleone B.,
and Shimizu N. (2016) Carbon and sulfur budget of the silicate Earth explained by accretion of differentiated planetary
embryos. Nat. Geosci. 9, 781–785) because C-solubility limit of 0.3 wt% in a S-rich alloy predicted by their models is significantly
lower than the experimentally derived C-solubility of 1.6 wt% for the relevant S-content in the core of the impactor.

Advanced Materials Interfaces: Chromiteen: A New 2D Oxide Magnetic Material from Natural Ore

Chromiteen: A New 2D Oxide Magnetic Material from Natural Ore

Advanced Materials Interfaces, 2018, 1800549. Posted by Gelu Costin

Thakur Prasad Yadav,* Sharmila N. Shirodkar, Narumon Lertcumfu, Sruthi Radhakrishnan, Farheen N. Sayed, Kirtiman Deo Malviya, Gelu Costin, Robert Vajtai, Boris I. Yakobson,* Chandra Sekhar Tiwary,* and Pulickel M. Ajayan*

The absence of inherent magnetism in the family of 2D materials limits its application in magnetoelectric and magnetic storage media. Here, a simple scalable route for the synthesis of magnetic 2D material chromite (chromiteen) via sonication-assisted liquid-phase exfoliation is demonstrated. The (111) plane of the exfoliated chromite is found to be the most stable which is confirmed by its common occurrence in exfoliation. Further, the stability and dispersion are verified by ab initio density functional theoretical simulations. Magnetic measurements over a large temperature range of 4 K ≤ T ≤ 300 K confirm ferromagnetic/superparamagnetic order with nearly 40 times higher magnetic moment saturation in chromiteen compared to chromite. The results reveal that 2D chromiteen causes a change in the magnetic behavior with respect to chromite which could be ascribed to the increase in the lattice strain as well as a magnetic strain due to high ferromagnetic
fraction in 2D plane.

Yadav, T. P., Shirodkar, S. N., Lertcumfu, N., Radhakrishnan, S., Sayed, F. N., Malviya, K. D., … Ajayan, P. M. (2018). Chromiteen: A New 2D Oxide Magnetic Material from Natural Ore. Advanced Materials Interfaces, 1800549.

https://doi.org/10.1002/admi.201800549

Nature Nanotechnology: Exfoliation of a non-van der Waals material from iron ore hematite

Exfoliation of a non-van der Waals material from iron ore hematite

Nature Nanotechnology, volume 13pages602–609 (2018), posted by Gelu Costin

Aravind Puthirath Balan 1,2,11, Sruthi Radhakrishnan1,11, Cristiano F. Woellner 3, Shyam K. Sinha4,
Liangzi Deng5, Carlos de los Reyes6, Banki Manmadha Rao7, Maggie Paulose7, Ram Neupane7,
Amey Apte1, Vidya Kochat1, Robert Vajtai 1, Avetik R. Harutyunyan8, Ching-Wu Chu5,9, Gelu Costin10,
Douglas S. Galvao3, Angel A. Martí6, Peter A. van Aken4, Oomman K. Varghese7, Chandra Sekhar Tiwary1*,
Anantharaman Malie Madom Ramaswamy Iyer1,2* and Pulickel M. Ajayan1*

Abstract
With the advent of graphene, the most studied of all two-dimensional materials, many inorganic analogues have been synthesized
and are being exploited for novel applications. Several approaches have been used to obtain large-grain, high-quality
materials. Naturally occurring ores, for example, are the best precursors for obtaining highly ordered and large-grain atomic
layers by exfoliation. Here, we demonstrate a new two-dimensional material ‘hematene’ obtained from natural iron ore hematite
(α -Fe2O3), which is isolated by means of liquid exfoliation. The two-dimensional morphology of hematene is confirmed by
transmission electron microscopy. Magnetic measurements together with density functional theory calculations confirm the
ferromagnetic order in hematene while its parent form exhibits antiferromagnetic order. When loaded on titania nanotube
arrays, hematene exhibits enhanced visible light photocatalytic activity. Our study indicates that photogenerated electrons can
be transferred from hematene to titania despite a band alignment unfavourable for charge transfer.

 

Citation: Balan, A. P., Radhakrishnan, S., Woellner, C. F., Sinha, S. K., Deng, L., Reyes, C. D. L., … Ajayan, P. M. (2018). Exfoliation of a non-van der Waals material from iron ore hematite. Nature Nanotechnology, 13pages 602–609.

https://doi.org/10.1038/s41565-018-0134-y

 

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