Science Advances: Crustal thickening and endogenic oxidation of magmatic sulfur

Ming Tang, Cin-Ty Lee, Wei-Qiang Ji, Rui Wang, Gelu Costin


Porphyry ore deposits, Earth’s most important resources of copper, molybdenum, and rhenium, are strongly associated with felsic magmas showing signs of high-pressure differentiation and are usually found in places with thickened crust (>45 kilometers). This pattern is well-known, but unexplained, and remains an outstanding problem in our understanding of porphyry ore deposit formation. We approach this problem by investigating the oxidation state of magmatic sulfur, which controls the behavior of ore-forming metals during magma differentiation and magmatic-hydrothermal transition. We use sulfur in apatite to reconstruct the sulfur oxidation state in the Gangdese batholith, southern Tibet. We find that magma sulfate content increased abruptly after India-Eurasia collision. Apatite sulfur content and the calculated magma S6+/ΣS ratio correlate with whole-rock dysprosium/ytterbium ratio, suggesting that residual garnet, favored in thickened crust, exerts a first-order control on sulfur oxidation in magmatic orogens. Our findings link sulfur oxidation to internal petrogenic processes and imply an intrinsic relationship of magma oxidation with synmagmatic crustal thickening.

Tang, M., Lee, C. A., Ji, W., Wang, R., & Costin, G. (2020). Crustal thickening and endogenic oxidation of magmatic sulfur. Science Advances, 6, 31, eaba6342. DOI: 10.1126/sciadv.aba6342



Nature Communications: Molecular hydrogen in minerals as a clue to interpret ∂D variations in the mantle

B. N. Moine, N. Bolfan-Casanova, I. B. Radu, D. A. Ionov, G. Costin, A. V. Korsakov, A. V. Golovin, O. B. Oleinikov, E. Deloule & J. Y. Cottin


Trace amounts of water dissolved in minerals affect density, viscosity and melting behaviour of the Earth’s mantle and play an important role in global tectonics, magmatism and volatile cycle. Water concentrations and the ratios of hydrogen isotopes in the mantle give insight into these processes, as well as into the origin of terrestrial water. Here we show the presence of molecular H2 in minerals (omphacites) from eclogites from the Kaapvaal and Siberian cratons. These omphacites contain both high amounts of H2 (70 to 460 wt. ppm) and OH. Furthermore, their ∂D values increase with dehydration, suggesting a positive H isotope fractionation factor between minerals and H2–bearing fluid, contrary to what is expected in case of isotopic exchange between minerals and H2O-fluids. The possibility of incorporation of large quantities of H as H2 in nominally anhydrous minerals implies that the storage capacity of H in the mantle may have been underestimated, and sheds new light on H isotope variations in mantle magmas and minerals.

Moine, B.N., Bolfan-Casanova, N., Radu, I.B. et al. Molecular hydrogen in minerals as a clue to interpret ∂D variations in the mantle. Nat Commun 11, 3604 (2020).

Nature Communications: Effects of climate change on the movement of future landfalling Texas tropical cyclones

Pedram Hassanzadeh, Chia-Ying Lee, Ebrahim Nabizadeh, Suzana J. Camargo, Ding Ma, and Laurence Y. Yeung

Nature Communications 11 (2020): 3319. doi: 10.1038/s41467-020-17130-7


The movement of tropical cyclones (TCs), particularly around the time of landfall, can substantially affect the resulting damage. Recently, trends in TC translation speed and the likelihood of stalled TCs such as Harvey have received significant attention, but findings have remained inconclusive. Here, we examine how the June-September steering wind and translation speed of landfalling Texas TCs change in the future under anthropogenic climate change. Using several large-ensemble/multi-model datasets, we find pronounced regional variations in the meridional steering wind response over North America, but―consistently across models―stronger June-September-averaged northward steering winds over Texas. A cluster analysis of daily wind patterns shows more frequent circulation regimes that steer landfalling TCs northward in the future. Downscaling experiments show a 10-percentage-point shift from the slow-moving to the fast-moving end of the translation-speed distribution in the future. Together, these analyses indicate increases in the likelihood of faster-moving landfalling Texas TCs in the late 21st century.

SedGeo: Eocene carbonate accumulation in the north-central Pacific Ocean: new insights from Ocean Drilling Program Site 1209, Shatsky Rise

Joyeeta Bhattacharya and Gerald R. Dickens
Major climate transitions and perturbations in global carbon cycle are known to have occurred during the Eocene, between 56 and 34 million years ago (Ma). A series of carbon isotope excursions (CIEs) mark variations in the global carbon cycle and changes in climate through early Eocene. Paleocene-Eocene Thermal Maximum(PETM) ca. 56 Ma is the most pronounced and well documented of these events expressed as a clay rich layer in many deep-sea sections, resulting from widespread carbonate dissolution on the seafloor, which is in turn re-lated to shoaling of the carbonate compensation depth (CCD) and lysocline. Other CIEs of early Eocene had similar response. However, response of these geologically ‘instantaneous’ hyperthermals differ from long-term warmth (multi-million-year time scale) of the Early Eocene Climate Optimum (EECO) in terms of sea-floor carbonate accumulation. Following the termination of EECO, earth’s climate transitioned into long-term cooling.Pronounced fluctuations in CCD of equatorial Pacific are known to have occurred during middle-late Eocene as well, whose global extent and origin are still unresolved. Most proxy records either span the interval of early Eocene or document particular climatic events in Eocene, which significantly limits visualizing the long-term Eocene climate change and response of open marine carbonate preservation. The present study documents change in carbonate dissolution and carbonate mass accumulation rate through the entire Eocene (56–34 Ma)at ODP Site 1209 on Shatsky Rise, north-central Pacific and ties it to a stable carbon and oxygen isotope record.Our study determines the correlation between deep-sea carbonate dissolution and carbon cycling process during the dynamic climate regime of Eocene. A strong correlation between magnitude of CIEs and intensity of dissolution for early Eocene hyperthermal events appears to significantly weaken for multiple dissolution events in middle-late Eocene, thereby indicating fundamental difference in their causal mechanism.

Bhattacharya, J., & Dickens, G. R. (2020). Eocene carbonate accumulation in the north-central Pacific Ocean: New insights from Ocean Drilling Program Site 1209, Shatsky Rise. Sedimentary Geology, 105705.

GCA: The speciation of carbon, nitrogen, and water in magma oceans and its effect on volatile partitioning between major reservoirs of the Solar System rocky bodies

GCA: The speciation of carbon, nitrogen, and water in magma oceans and its effect on volatile partitioning between major reservoirs of the Solar System rocky bodies

Damanveer S. Grewal, Rajdeep Dasgupta, Alexandra Farnell

The composition of atmospheres and the resulting potential for planetary habitability in the rocky bodies of our Solar System and beyond is strongly controlled by the volatile exchange between their silicate reservoirs and exospheres. The initial budget and speciation of major volatiles, like carbon (C), nitrogen (N) and water (H2O), in the silicate reservoirs and atmospheres was set during the formation stages of rocky bodies. However, the speciation of these major volatiles in reduced silicate melts prevalent during the differentiation stages of rocky bodies and its effect on the partitioning of volatiles between major rocky body reservoirs is poorly known. Here we present SIMS and vibrational spectroscopy (FTIR and Raman) data, determining C solubility, H content, and speciation of mixed C-O-N-H volatiles in graphite saturated silicate glasses from high P (1–7 GPa)-T (1500–2200 °C) experiments reported in Grewal et al., 2019aGrewal et al., 2019b. The experiments recorded oxygen fugacity (log fO2) between IW–4.3 and IW–0.8. C-O-N-H speciation varied systematically as function of fO2 at any given PT. We find out that C-NCO32-, N2, and OH are the dominant species in the oxidized range (>IW–1.5), along with some contributions from C-H, N-H, and C-O bearing species. Between IW–3.0 and IW–1.5, C is bonded as C-O either in the form of isolated C-O molecules or Fe-carbonyl complexes, or as C-H in hydrocarbons, or as combination of both in esters, while almost all of the H is bonded with the dominant N species, i.e., NH2− or NH2-. At the most reduced conditions (<IW–3.0), C is present mostly in the form of C-H bearing species, while anhydrous N3− followed by N-H bearing molecules are the dominant N bearing species. Magma oceans (MOs) in highly reduced bodies like Mercury would contain most of their C as graphite if MO is carbon saturated and the dissolved C and N would be chemically bonded with the silicate network either in the form of anhydrous C4− and N3−, or hydrogenated C-H and N-H bearing species depending on H content of the silicate melts. MOs relevant for Mars, the Moon, Vesta, and angrite parent body would contain C and N mostly in the form of C-O and N-H bearing species, respectively. If the composition of Earth’s accreting material evolved from reduced to oxidized, then initially a significant amount of the C and N budget would be locked in the silicate reservoirs, which would subsequently be released to the proto-atmosphere(s) at later stages. The retention of proto-atmosphere(s) formed by MO degassing on Earth could have provided important precursors for prebiotic chemistry which possibly led to the eventual habitability of our planet. Additionally, based on the dominant speciation of N versus C in silicate melt as a function of fO2, we also predict that DNalloy/silicate is unaffected by fH2 under highly reduced conditions (<IW–3), while DCalloy/silicate is affected. Therefore, caution must be taken during the application of experimentally determined DNalloy/silicate and DCalloy/silicate to nominally anhydrous MOs.

Grewal, D. S., Dasgupta, R., & Farnell, A. (2020). The speciation of carbon, nitrogen, and water in magma oceans and its effect on volatile partitioning between major reservoirs of the Solar System rocky bodies. Geochimica et Cosmochimica Acta 280: 281-301. doi:10.1016/j.gca.2020.04.023

JGR Planets: The solidus and melt productivity of nominally anhydrous Martian mantle constrained by new high pressure-temperature experiments – Implications for crustal production and mantle source evolution

Shuo Ding, Rajdeep Dasgupta, Kyusei Tsuno


Abstract: We constrained the solidus of a model Martian composition with low bulk Mg# (molar MgO/(MgO + FeOT) × 100 ~75) and high total alkali (Na2O + K2O = 1.09 wt.%) concentration at 2 to 5 GPa by experiments. Based on the new solidus brackets, we provide a new parameterization of the solidus temperature as a function of pressure of Martian mantle: Ts (°C) = − 5P (GPa)2 + 107P(GPa) + 1,068. The newly constrained solidus of the Lodders and Fegley (1997; model Martian composition (LF composition) is 20 to 90 °C lower than the previous solidus of model Martian mantle with lower total alkali (~0.54 wt.%). The supersolidus experiments yield an average isobaric melt productivity, dF/dT, of 20 ± 6 wt.%/100 °C. We also bracketed the solidi of model Martian mantle compositions with low Mg# (~75) and low alkali (~0.54 wt.%), and with high Mg# (~80) and low alkali (~0.54 wt.%) at a constant pressure of 3 GPa. We find that bulk Mg# enhances the solidus temperature and bulk total alkalis suppress it. A parameterization that estimates the effect of bulk Mg# and total alkalis on peridotite solidus, including Mars and Earth, at 3 GPa can be described as: Ts(°C) = 4.23Mg # − 85(Na2O(wt. %) + K2O(wt. %)) + 1,120. Based on the new solidus parameterizations, 10–40 km more Martian crust would be produced by columnar decompression melting for LF model composition compared to the low Mg#‐low alkali model composition. The quantitative constraints on the solidus shift with Mg# and total alkalis from this study can be used to assess the Martian mantle solidus change through melting and melt extraction over time and the role of mantle heterogeneity in crustal production.


Ding, S., Dasgupta, R. & Tsuno, K. (2020). The solidus and melt productivity of nominally anhydrous Martian mantle constrained by new high pressure-temperature experiments – Implications for crustal production and mantle source evolution. Journal of Geophysical Research – Planets 123, e2019JE006078. doi:10.1029/2019JE006078

AGU Monograph: The effect of variable Na/K on CO2 solubility in slab-derived rhyolitic melts

The effect of variable Na/K on CO2 solubility in slab-derived rhyolitic melts


Michelle Muth, Megan S. Duncan, Rajdeep Dasgupta


Abstract: We conducted high pressure, high temperature experiments to investigate the effect of variable alkali ratio on the CO2‐rich fluid solubility in hydrous rhyolitic melts at sub‐arc depths. Experiments were performed at 3.0 and 1.5 GPa, 1300 °C on rhyolitic compositions similar to low‐degree partial melts of subducted slab lithologies, with fixed total alkalis (Na2O+K2O ~11.5 wt.%, volatile‐free), but Na# (molar Na2O/[Na2O+K2O]) varying from 0.15 to 0.88. In the experimental glasses, total dissolved CO2 (CO2tot.) ranged from 2.14 ± 0.07 to 3.20 ± 0.07 wt.% at 3.0 GPa, and from 0.70 ± 0.02 to 1.19 ± 0.02 wt.% at 1.5 GPa. Experiments showed a general positive correlation between Na# and CO2tot., with the exception of the highest Na# experiment at 1.5 GPa. Carbon was dissolved as molecular CO2 (CO2mol.) and carbonate (CO32‐). As Na# increased, CO2mol./CO2tot. decreased from 0.94 to ~0.00 in the 1.5 GPa experiments and from 0.65 to 0.05 in the 3.0 GPa experiments. Variability in CO2 concentration is larger and more clearly correlated with Na# at 3.0 GPa, indicating that this effect is pressure dependent. Our results show that compositional variability in silicic melts must be considered to accurately place constraints on the limit of CO2 transfer in subduction zones.


Muth, M., Duncan, M. S., Dasgupta, R. (2020). The effect of variable Na/K on CO2 solubility in slab-derived rhyolitic melts. In Manning, C., Lin, A., and Mao, W. (Eds.) Carbon in Earth’s Interior, Geophysical Monograph 249, 195-208. doi:10.1002/9781119508229.ch17

Mineralium Deposita: Hybrid norite and the fate of argillaceous to anhydritic shales assimilated by Bushveld melts

Yudovskaya, M. A., Costin, G., Sluzhenikin, S. F., Kinnaird, J. A., Ueckermann, H., & Abramova, V. D.


Mafic sills of the Marginal Zone are widespread within the footwall of the Bushveld Complex with some of them being enclosed in later Bushveld intrusions. In the central sector of the northern limb of the Bushveld Complex on the Turfspruit farm, a sill of norite enclosed within the Lower Zone cumulates contains numerous semi-assimilated fragments of anorthositic and magnetite-orthopyroxenitic lithologies that are interpreted to be the partially melted xenoliths of local argillaceous, magnetite-bearing, and anhydritic shales. Almost pure anorthite with eutectic inclusions of microgranular Al-rich orthopyroxene composes the interstitial material in the Lower Zone chromite-olivine cumulates at the contact with the magnetite-bearing norite. An identical association of anorthite+Al-rich orthopyroxene occurs in the overlying Platreef pyroxenite at the contact with anhydritic hornfels suggesting that an exchange reaction has likely involved anhydrite in both cases. Strontium isotope signatures of plagioclase from the norite support its hybrid origin, whereas Sr isotopes in anorthite from harzburgite is within the range of the most primitive Bushveld rocks indicating a predominant contribution of magmatic Sr. We suggest that the observed mineral assemblages of Al-rich and Cr-poor orthopyroxene, Fe-rich anorthite with elevated Ga, and Al-rich, Cr-depleted spinel, as well as the changes in mineral chemistries towards those compositions, are indicative of assimilation of evaporites and argillaceous shales by Bushveld melts on Turfspruit and elsewhere in the northern limb.


Yudovskaya, M.A., Costin, G., Sluzhenikin, S.F. et al. (2020). Hybrid norite and the fate of argillaceous to anhydritic shales assimilated by Bushveld melts. Miner Deposita.

J Petrol: Non-sequential injection of PGE-rich ultramafic sills in the Platreef Unit at Akanani, Northern Limb of the Bushveld Complex: Evidence from Sr and Nd isotopic systematics

Roger N Scoon, Gelu Costin, Andrew Mitchell, Bertrand Moine


The Platreef Unit is a deceptively complex sequence of layered cumulates located in the northern limb of the 2.055 Ga-old Bushveld Complex. The unit includes the Platreef, a thick, richly mineralized stratabound PGE orebody which differs markedly from the comparatively thin, predominantly stratiform Merensky Reef found in the Upper Critical Zone of the eastern and western limbs. The Platreef Unit is, however, interpreted as a localized facies of the Upper Critical Zone, despite layering being neither as systematic nor as clearly defined as in the equivalent stratigraphy found in the other limbs. The Platreef Unit in the Akanani project area includes well-defined layers of feldspathic harzburgite and norite, in addition to the ubiquitous feldspathic orthopyroxenite-melanorite that characterizes other sections. The paucity of floor-rock xenoliths is an additional feature. The relatively well-developed nature of the layering and paucity of xenoliths in the Platreef Unit at Akanani is explained by separation of the unit from the floor of the intrusion by a thick succession of ultramafics assigned to the Lower Critical Zone. We identify three lithological subgroups in the Platreef Unit at Akanani. They do not define an upward-younging stratigraphy. The primary stratigraphy, or PU1 subunit, is dominated by multiple layers of feldspathic orthopyroxenite, melanorite, and norite. This subunit built up from incremental addition of relatively small magma pulses. Repeated magma replenishment induced concomitant partial melting of earlier-formed layers. The PU1 subunit includes thin chromite stringers that contain Cr-spinels with unusual, amoeboidal textures consistent with several stages of growth and re-equilibration. The feldspathic harzburgite of the younger PU2 subunit was emplaced non-sequentially into the already complexly-layered PU1 subunit as a series of sinuous lenses or syn-intrusive sills. One of the PU2 sills contains the richest and most consistent of the mineralized sections at Akanani, i.e., the Main Mineralized Reef (MMR). The irregularly-developed pegmatoidal lithologies of the PU3 subunit are ascribed to the recrystallization of earlier-formed cumulates (PU1 and PU2).

Whole-rock isotopic data for a section of the Platreef Unit, together with the overlying Lower Main Zone and underlying Lower Critical Zone, mostly from drill-hole ZF-1, demonstrate a complex pattern in both Sr87/Sr86 initial ratios and ԐNd values. These patterns are consistent with multiple lineages of parental magmas. The Lower Main Zone and the majority of the Platreef Unit are characterized by anomalously high Sr initial ratios (with a large degree of scatter) and low ԐNd values (relatively tightly constrained). Harzburgite layers from the Lower Critical Zone have a low Sr initial ratio and a relatively high ԐNd value. The new isotopic data suggest these sequences crystallized from multiple magma batches, broadly constrained within the U-type (ultramafic) and A-type (tholeiitic) lineages, derived from mantle sources and/or staging chambers which experienced varying degrees of crustal contamination. The MMR crystallized from a specific pulse of the U-type magma lineage characterized by a high Sr87/Sr86 initial ratio (average of 0.71113) and a markedly low ԐNd value (average of -11.35). The olivine-saturated magmas associated with the MMR were derived from a localized mantle source and yet underwent an unusually high degree of crustal contamination. Some of the layered PGE orebodies in the Bushveld Complex, including the Platreef and Merensky Reef, were emplaced as syn-magmatic sills which crystallized from anomalously PGE-rich parental magmas with a unique isotopic fingerprint.

Scoon, R.N., Costin, G.,  Mitchell, A., Moine, B. (2020). Non-sequential injection of PGE-rich ultramafic sills in the Platreef Unit at Akanani, Northern Limb of the Bushveld Complex: Evidence from Sr and Nd isotopic systematics, Journal of Petrology, egaa032,

Scientific Reports: Monomineralic anorthosites in layered intrusions are indicators of the magma chamber replenishment by plagioclase-only-saturated melts

Rais Latypov, Sofya Chistyakova, Gelu Costin, Olivier Namur, Steve Barnes & Willem Kruger


The formation of some Earth’s monomineralic igneous rocks appears to be prohibited by constraints imposed by liquidus phase-equilibria on the evolution of mantle-derived magmas. Yet, these rocks exist as stratiform layers in many mafic-ultramafic intrusions. One conspicuous example is monomineralic anorthosites in the Bushveld Complex that occur as stratiform layers up to hundreds of kilometres in length. Such monomineralic anorthosites appear to require parental melts saturated in plagioclase only but where and how to produce these melts remains a contentious issue. Here we argue that they are likely sourced from deep-seated magma reservoirs. In response to pressure reduction, these ascending melts become first superheated and then saturated in plagioclase after stalling and cooling in shallow-level chambers. Adcumulus growth of plagioclase from such melts at the chamber floor results in the formation of monomineralic anorthosites. We propose that stratiform layers of monomineralic anorthosites in layered intrusions are products of the chamber replenishment by melts whose saturation in plagioclase as a single liquidus phase is triggered by their transcrustal ascent towards the Earth’s surface.

Latypov, R., Chistyakova, S., Costin, G., Namur, O. & Barnes, S. (2020). Monomineralic anorthosites in layered intrusions are indicators of the magma chamber replenishment by plagioclase-only-saturated melts. Scientific Reports. Springer US 1–14.