Bayerisches Geoinstitut

27/12/2019

A new article:

Serovaiskii, A., Mukhina, E., Dubrovinsky, L., Chernoutsan, A., Kudryavtsev, D., McCammon, C., Aprilis, G., Kupenko, I., Chumakov, A., Hanfland, M., Kutcherov, V., 2019.
Fate of Hydrocarbons in Iron-Bearing Mineral Environments during Subduction.
Minerals 9, 11.

Abstract
Subducted sediments play a key role in the evolution of the continental crust and upper mantle. As part of the deep carbon cycle, hydrocarbons are accumulated in sediments of subduction zones and could eventually be transported with the slab below the crust, thus affecting processes in the deep Earth's interior. However, the behavior of hydrocarbons during subduction is poorly understood. We experimentally investigated the chemical interaction of model hydrocarbon mixtures or natural oil with ferrous iron-bearing silicates and oxides (representing possible rock-forming materials) at pressure-temperature conditions of the Earth's lower crust and upper mantle (up to 2000(+/- 100) K and 10(+/- 0.2) GPa), and characterized the run products using Raman and Mossbauer spectroscopies and X-ray diffraction. Our results demonstrate that complex hydrocarbons are stable on their own at thermobaric conditions corresponding to depths exceeding 50 km. We also found that chemical reactions between hydrocarbons and ferrous iron-bearing rocks during slab subduction lead to the formation of iron hydride and iron carbide. Iron hydride with relatively low melting temperature may form a liquid with negative buoyancy that could transport reduced iron and hydrogen to greater depths.

19/12/2019

A new article:

Moussallam, Y., Longpre, M.A., McCammon, C., Gomez-Ulla, A., Rose-Koga, E.F., Scaillet, B., Peters, N., Gennaro, E., Paris, R., Oppenheimer, C., 2019. Mantle plumes are oxidised. Earth Planet. Sci. Lett. 527, 10.
https://doi.org/10.1016/j.epsl.2019.115798

From oxic atmosphere to metallic core, the Earth's components are broadly stratified with respect to oxygen fugacity. A simple picture of reducing oxygen fugacity with depth may be disrupted by the accumulation of oxidised crustal material in the deep lower mantle, entrained there as a result of subduction. While hotspot volcanoes are fed by regions of the mantle likely to have incorporated such recycled material, the oxygen fugacity of erupted hotspot basalts had long been considered comparable to or slightly more oxidised than that of mid-ocean ridge basalt (MORB) and more reduced than subduction zone basalts. Here we report measurements of the redox state of glassy crystal-hosted melt inclusions from tephra and quenched lava samples from the Canary and Cape Verde Islands, that we can independently show were entrapped prior to extensive sulphur degassing. We find high ferric iron to total iron ratios (Fe3+/Sigma Fe) of up to 0.27-0.30, indicating that mantle plume primary melts are significantly more oxidised than those associated with mid-ocean ridges and even subduction zone. These results, together with previous investigations from the Erebus, Hawaiian and Icelandic hotspots, confirm that mantle upwelling provides a return flow from the deep Earth for components of oxidised subducted lithosphere and suggest that highly oxidised material accumulates or is generated in the lower mantle. The oxidation state of the Earth's interior must therefore be highly heterogeneous and potentially locally inversely stratified. (C) 2019 Elsevier B.V. All rights reserved.

https://www.sciencedirect.com/science/article/pii/S0012821X1930490X

From oxic atmosphere to metallic core, the Earth's components are broadly stratified with respect to oxygen fugacity. A simple picture of reducing oxy…

19/12/2019

A new article:

Iizuka-Oku, R., Soustelle, V., Miyajima, N., Walte, N.P., Frost, D.J., Yagi, T., 2019. Experimentally deformed lawsonite at high pressure and high temperature: Implication for low velocity layers in subduction zones. Phys. Earth Planet. Inter. 295, 106282.
https://doi.org/10.1016/j.pepi.2019.106282

Abstract
Lawsonite is considered to be one of the most likely hydrous minerals to explain the persistence of seismic low-velocity layers (LVLs) atop subducted slabs to depths of 100–250 km due mainly to the fact that it can persist to these depths, in contrast to other hydrous minerals such as antigorite. However, as it is highly anisotropic and subjected to intense deformation during subduction, further constrains on the development of lawsonite crystal preferred orientation (CPO) at high pressure and temperature are required in order to evaluate its role in slowing seismic waves. We have deformed lawsonite aggregates at 5 GPa and 500–800 °C corresponding to 150 km depth and covering temperatures for both cold and hot subduction zones. In this study, we report a new lawsonite CPO pattern resulting from dislocation creep deformation that has not been previously observed. The [100] axes concentrate into the shear direction and the [010] axes are normal to the shear plane, respectively (we refer to this as “type-1” CPO). Such CPO is consistent with our transmission electron microscope (TEM) observations identifying (010)[100] as a dominant dislocation slip-system. The seismic properties resulting from this CPO show the fast P-wave direction to be parallel to the shear direction, and the slow P-wave direction and maximum S-wave anisotropy normal to the shear plane. We performed calculation of omphacite-lawsonite aggregates using our experimental data and varied both the lawsonite contents and the slab dipping angle. Our results show that a reasonable amount of lawsonite can explain Vs reduction in the LVLs, but cannot explain the Vp reduction. However, the presence of lawsonite would induce a rotation of the fast S-wave polarization toward the trench direction as the S-wave anisotropy increases or decreases according to the lawsonite proportion, its CPO strength and the slab dipping angle. We believe that our calculation can now be used for investigation of lawsonite effect in various subductions zones.

https://www.sciencedirect.com/science/article/pii/S0031920118302413?via%3Dihub

Lawsonite is considered to be one of the most likely hydrous minerals to explain the persistence of seismic low-velocity layers (LVLs) atop subducted …

19/12/2019

A new article:

Vogel, S., Bykov, M., Bykova, E., Wendl, S., Kloß, S.D., Pakhomova, A., Dubrovinskaia, N., Dubrovinsky, L. and Schnick, W. (2019), Nitride Spinel: An Ultraincompressible High‐Pressure Form of BeP2N4. Angew. Chem. Int. Ed.. doi:10.1002/anie.201910998

Abstract

Owing to its outstanding elastic properties, the nitride spinel γ‐Si3N4 is of considered interest for materials scientists and chemists. DFT calculations suggest that Si3N4‐analog beryllium phosphorus nitride BeP2N4 adopts the spinel structure at elevated pressures as well and shows outstanding elastic properties. Herein, we investigate phenakite‐type BeP2N4 by single‐crystal synchrotron X‐ray diffraction and report the phase transition into the spinel‐type phase at 47 GPa and 1800 K in a laser‐heated diamond anvil cell. The structure of spinel‐type BeP2N4 was refined from pressure‐dependent in situ synchrotron powder X‐ray diffraction measurements down to ambient pressure, which proves spinel‐type BeP2N4 a quenchable and metastable phase at ambient conditions. Its isothermal bulk modulus was determined to 325(8) GPa from equation of state, which indicates that spinel‐type BeP2N4 is an ultraincompressible material.

19/12/2019

A new article:

Petrology and oxygen isotopic composition of large igneous inclusions in ordinary chondrites: Early solar system igneous processes and oxygen reservoirs

Ruzicka, Alex M.; Greenwood, Richard C.; Armstrong, Katherine; Schepker, Kristy L.; Franchi, Ian A.

Geochimica Et Cosmochimica Acta
https://doi.org/10.1016/j.gca.2019.01.017

Abstract

Large (>3.5 mm and up to 4 cm across) igneous inclusions poor in metal and sulfide are a minor but not uncommon component in ordinary chondrites, and have implications for the nature of physiochemical and melting processes in the early solar system. We obtained petrographic-chemical data for forty-two large igneous inclusions in ordinary chondrites of various groups (H, L, LL) and petrographic types (3–6) and oxygen isotope data for a subset of twelve of these inclusions and their host chondrites. Different inclusions formed both before and after the thermal metamorphism experienced by their host chondrites. The bulk chemical compositions of the inclusions vary broadly around whole-rock chondrite composition, comprise four main chemical types and some other variants, and show little evidence of having formed as igneous differentiates. Oxygen isotope compositions overlap ordinary chondrite compositions and are related to inclusion chemical type. Most prevalent in type 3 and 4 chondrites are inclusions, often droplets, of the vapor-fractionated (Vfr) chemical type, either enriched in refractory lithophile elements, or depleted in volatile lithophile elements, or both. These inclusions have low Δ17O (∼0.1–0.6‰) and high δ18O (∼4–8‰) values and formed in reservoirs with Δ17O lower than their hosts, primarily as evaporative melts and mixtures that probably experienced kinetic isotopic fractionation. Another chemical type (Unfr + K) has unfractionated abundances of lithophile elements except for being strongly enriched in K, a signature also found in some impact melts from melt rocks and melt breccias. These inclusions formed by impact melting of chondritic material and accompanying K enrichment. Inclusions with unfractionated (Unfr) lithophile element abundances are present in type 3–6 chondrites and are prevalent in type 5 and 6. Some are spatially associated with coarse metal-sulfide nodules in the chondrites and likely formed by in situ impact melting. Others were melted prior to thermal metamorphism and were chemically but not isotopically homogenized during metamorphism; they are xenoliths that formed in oxygen reservoirs different than the hosts in which they were metamorphosed. The latter inclusions provide evidence for nebular or collisional mixing of primitive materials prior to thermal metamorphism of asteroid bodies, including transport of H-like source materials to the L body, LL-like source materials to the L body, and low-Δ17O materials to the LL body. Feldspar-rich (FldR) inclusions have compositions similar to melt pockets and could have formed by disequilibrium melting and concentration of feldspar during an impact event to form large droplets or large masses. Overall, the results of this study point to important and varied roles for both “planetary” impact melting and “nebular” evaporative melting processes to form different large igneous inclusions in ordinary chondrites. Chondrules may have formed by processes similar to those inferred for large inclusions, but there are important differences in the populations of these objects.

https://www.sciencedirect.com/science/article/pii/S0016703719300304?via%3Dihub

19/12/2019

A new article


Eichheimer, P., Thielmann, M., Popov, A., Golabek, G. J., Fujita, W., Kottwitz, M. O., and Kaus, B. J. P.:
Pore-scale permeability prediction for Newtonian and non-Newtonian fluids, Solid Earth, 10, 1717–1731, https://doi.org/10.5194/se-10-1717-2019, 2019.

Abstract

The flow of fluids through porous media such as groundwater flow or magma migration is a key process in geological sciences. Flow is controlled by the permeability of the rock; thus, an accurate determination and prediction of its value is of crucial importance. For this reason, permeability has been measured across different scales. As laboratory measurements exhibit a range of limitations, the numerical prediction of permeability at conditions where laboratory experiments struggle has become an important method to complement laboratory approaches. At high resolutions, this prediction becomes computationally very expensive, which makes it crucial to develop methods that maximize accuracy. In recent years, the flow of non-Newtonian fluids through porous media has gained additional importance due to, e.g., the use of nanofluids for enhanced oil recovery. Numerical methods to predict fluid flow in these cases are therefore required.

Here, we employ the open-source finite difference solver LaMEM (Lithosphere and Mantle Evolution Model) to numerically predict the permeability of porous media at low Reynolds numbers for both Newtonian and non-Newtonian fluids. We employ a stencil rescaling method to better describe the solid–fluid interface. The accuracy of the code is verified by comparing numerical solutions to analytical ones for a set of simplified model setups. Results show that stencil rescaling significantly increases the accuracy at no additional computational cost. Finally, we use our modeling framework to predict the permeability of a Fontainebleau sandstone and demonstrate numerical convergence. Results show very good agreement with experimental estimates as well as with previous studies. We also demonstrate the ability of the code to simulate the flow of power-law fluids through porous media. As in the Newtonian case, results show good agreement with analytical solutions.

https://www.solid-earth.net/10/1717/2019/se-10-1717-2019.html

The flow of fluids through porous media such as groundwater flow or magma migration is a key process in geological sciences. Flow is controlled by the permeability of the rock; thus, an accurate determination and prediction of its value is of crucial importance. For this reason, permeability has bee...

19/12/2019

New colleague: Lianjie Man comes from the University of science and technology of China where he received a MSc in Geosciences with an experimental thesis about the reaction between carbon and bridgmanite under the P,T conditions of the lower mantle. At BGI he will work on his PhD with Dan Frost investigating the composition of the Earth’s core with diamond anvil cell experiments.
Welcome to BGI and all the best, Lianjie !

19/12/2019

A new paper

Effect of Fe3+ on Phase Relations in the Lower Mantle: Implications for Redox Melting in Stagnant Slabs

Ryosuke Sinmyo Yoichi Nakajima Catherine A. McCammon Nobuyoshi Miyajima Sylvain Petitgirard Robert Myhill Leonid Dubrovinsky Daniel J. Frost

Journal of Geophysical Research: Solid Earth, 124. https://doi.org/10.1029/2019JB017704

Recent studies have revealed that Earth's deep mantle may have a wider range of oxygen fugacities than previously thought. Such a large heterogeneity might be caused by material subducted into the deep mantle. However, high‐pressure phase relations are poorly known in systems including Fe3+ at the top of the lower mantle, where the subducted slab may be stagnant. We therefore conducted high‐pressure and high‐temperature experiments using a multi‐anvil apparatus to study the phase relations in a Fe3+‐bearing system at 26 GPa and 1573–2073 K, at conditions prevailing at the top of the lower mantle. At temperatures below 1923 K, MgSiO3‐rich bridgmanite, an Fe3+‐rich oxide phase, and SiO2 coexist in the recovered sample. Quenched partial melt was observed above 1973 K, which is significantly lower than the solidus temperature of an equivalent Fe3+‐free bulk composition. The partial melt obtained from the Fe3+‐rich bulk composition has a higher iron content than coexisting bridgmanite, similar to the Fe2+‐dominant system. The results suggest that strong mantle oxygen fugacity anomalies might alter the subsolidus and melting phase relations under lower mantle conditions. We conclude that (1) a small amount of melt may be generated from an Al‐depleted region of a stagnant slab, such as subducted former banded‐iron‐formation, and (2) Fe3+ is not transported into the deep part of the lower mantle because of its incompatibility during melting.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JB017704

11/12/2019

A new article

Imbrium Age for Zircons in Apollo 17 South Massif Impact Melt Breccia 73155

Bidong Zhang, Yangting Lin, Desmond E. Moser, The Apollo 17 poikilitic impact melt breccias were initially interpreted to be directly related to the Serenitatis basin formation. Here we present petrological, geochemical, and U-Pb geochronological investigations of the poikilitic impact melt of Apollo 73155,69 which was sampled from the South Massif of the Taurus-Littrow valley. Nanoscale secondary ion mass spectrometry analyses of well-preserved poikilitic zircons from sample 73155,69 yield a uniform Pb-207/Pb-206 age population with a weighted mean age of 3921 +/- 14 Ma. The zircons have distinctly high concentrations of Y (3279-6347 ppm) and Th (254-302 ppm) compared with other Apollo 17 zircons. These characteristics, together with their textures, are remarkably similar to those of zircons from high-Th melt breccias from Apollo 12 samples and lunar meteorite Sayh al Uhaymir 169 attributed to the formation of the high-Th deposits of the Imbrium basin. We therefore propose an Imbrium provenance for melt component in 73155,69. Our results provide new evidence for components of Imbrium-type ejecta occurring among the South Massif breccias. Consequently, the Apollo 17 poikilitic impact melt breccias may not represent Serenitatis ejecta.Jialong Hao, Sean R. Shieh, Audrey Bouvier
First published: 15 November 2019

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2019JE005992

Impact‐grown poikilitic zircons are found in Apollo 17 breccia 73155 from the South Massif The 73155 zircons have age, texture, and trace element concentrations identical to the zircons from repres...

04/12/2019

New colleague:

Liang Yuan has completed his Ph.D. as an associate member of the IRTG at Tohoku University with a thesis on the mineral physics of volatile bearing phases in the Earth's mantle. In his research he has combined diamond anvil cell experiments and ab initio simulations. For his postdoctoral work he wants to focus on simulations on melting of mineral phases in the Earth's lower mantle and conditions of super-Earth interiors, working with Gerd Steinle-Neumann. Welcome to BGI and all the best, Liang!

04/12/2019

Article

Mantle plumes are oxidised
Moussallam, Y; Longpre, MA; McCammon, C; Gomez-Ulla, A; Rose-Koga, EF; Scaillet, B; Peters, N; Gennaro, E; Paris, R; Oppenheimer, C
EARTH AND PLANETARY SCIENCE LETTERS
Volume: 527 Published: DEC 1 2019
DOI: 10.1016/j.epsl.2019.115798

From oxic atmosphere to metallic core, the Earth's components are broadly stratified with respect to oxygen fugacity. A simple picture of reducing oxygen fugacity with depth may be disrupted by the accumulation of oxidised crustal material in the deep lower mantle, entrained there as a result of subduction. While hotspot volcanoes are fed by regions of the mantle likely to have incorporated such recycled material, the oxygen fugacity of erupted hotspot basalts had long been considered comparable to or slightly more oxidised than that of mid-ocean ridge basalt (MORB) and more reduced than subduction zone basalts. Here we report measurements of the redox state of glassy crystal-hosted melt inclusions from tephra and quenched lava samples from the Canary and Cape Verde Islands, that we can independently show were entrapped prior to extensive sulphur degassing. We find high ferric iron to total iron ratios (Fe3+/Sigma Fe) of up to 0.27-0.30, indicating that mantle plume primary melts are significantly more oxidised than those associated with mid-ocean ridges and even subduction zone. These results, together with previous investigations from the Erebus, Hawaiian and Icelandic hotspots, confirm that mantle upwelling provides a return flow from the deep Earth for components of oxidised subducted lithosphere and suggest that highly oxidised material accumulates or is generated in the lower mantle. The oxidation state of the Earth's interior must therefore be highly heterogeneous and potentially locally inversely stratified. (C) 2019 Elsevier B.V. All rights reserved.

From oxic atmosphere to metallic core, the Earth's components are broadly stratified with respect to oxygen fugacity. A simple picture of reducing oxy…

15/11/2019

Weekly seminar: "Subduction & Water: from the surface to the deep Earth" by Valentina Magni (Centre for Earth Evolution and Dynamics University of Oslo)