TY - JOUR A1 - Spallanzani, Roberta A1 - Koga, Kenneth T. A1 - Cichy, Sarah B. A1 - Wiedenbeck, Michael A1 - Schmidt, Burkhard C. A1 - Oelze, Marcus A1 - Wilke, Max T1 - Lithium and boron diffusivity and isotopic fractionation in hydrated rhyolitic melts JF - Contributions to mineralogy and petrology N2 - Lithium and boron are trace components of magmas, released during exsolution of a gas phase during volcanic activity. In this study, we determine the diffusivity and isotopic fractionation of Li and B in hydrous silicate melts. Two glasses were synthesized with the same rhyolitic composition (4.2 wt% water), having different Li and B contents; these were studied in diffusion-couple experiments that were performed using an internally heated pressure vessel, operated at 300 MPa in the temperature range 700-1250 degrees C for durations from 0 s to 24 h. From this we determined activation energies for Li and B diffusion of 57 +/- 4 kJ/mol and 152 +/- 15 kJ/mol with pre-exponential factors of 1.53 x 10(-7) m(2)/s and 3.80 x 10(-8) m(2)/s, respectively. Lithium isotopic fractionation during diffusion gave beta values between 0.15 and 0.20, whereas B showed no clear isotopic fractionation. Our Li diffusivities and isotopic fractionation results differ somewhat from earlier published values, but overall confirm that Li diffusivity increases with water content. Our results on B diffusion show that similarly to Li, B mobility increases in the presence of water. By applying the Eyring relation, we confirm that B diffusivity is limited by viscous flow in silicate melts. Our results on Li and B diffusion present a new tool for understanding degassing-related processes, offering a potential geospeedometer to measure volcanic ascent rates. KW - stable isotopes KW - diffusion KW - isotopic fractionation KW - hydrated silicate KW - melts Y1 - 2022 U6 - https://doi.org/10.1007/s00410-022-01937-2 SN - 0010-7999 SN - 1432-0967 VL - 177 IS - 8 PB - Springer CY - New York ER - TY - JOUR A1 - Krstulović, Marija A1 - Rosa, Angelika D. A1 - Ferreira Sanchez, Dario A1 - Libon, Lélia A1 - Albers, Christian A1 - Merkulova, Margarita A1 - Grolimund, Daniel A1 - Irifune, Tetsuo A1 - Wilke, Max T1 - Effect of temperature on the densification of silicate melts to lower earth's mantle conditions JF - Physics of the earth and planetary interiors N2 - Physical properties of silicate melts play a key role for global planetary dynamics, controlling for example volcanic eruption styles, mantle convection and elemental cycling in the deep Earth. They are significantly modified by structural changes at the atomic scale due to external parameters such as pressure and temperature or due to chemistry. Structural rearrangements such as 4- to 6-fold coordination change of Si with increasing depth may profoundly influence melt properties, but have so far mostly been studied at ambient temperature due to experimental difficulties. In order to investigate the structural properties of silicate melts and their densification mechanisms at conditions relevant to the deep Earth's interior, we studied haplo basaltic glasses and melts (albite-diopside composition) at high pressure and temperature conditions in resistively and laser-heated diamond anvil cells using X-ray absorption near edge structure spectroscopy. Samples were doped with 10 wt% of Ge, which is accessible with this experimental technique and which commonly serves as a structural analogue for the network forming cation Si. We acquired spectra on the Ge K edge up to 48 GPa and 5000 K and derived the average Ge-O coordination number NGe-O, and bond distance RGe-O as functions of pressure. Our results demonstrate a continuous transformation from tetrahedral to octahedral coordination between ca. 5 and 30 GPa at ambient temperature. Above 1600 K the data reveal a reduction of the pressure needed to complete conversion to octahedral coordination by ca. 30 %. The results allow us to determine the influence of temperature on the Si coordination number changes in natural melts in the Earth's interior. We propose that the complete transition to octahedral coordination in basaltic melts is reached at about 40 GPa, corresponding to a depth of ca. 1200 km in the uppermost lower mantle. At the core-mantle boundary (2900 km, 130 GPa, 3000 K) the existence of non-buoyant melts has been proposed to explain observed low seismic wave velocity features. Our results highlight that the melt composition can affect the melt density at such extreme conditions and may strongly influence the structural response. KW - Silicate melts KW - Densification KW - High pressure and high temperature; KW - XANES KW - Coordination number KW - Ultra-low velocity zones Y1 - 2022 U6 - https://doi.org/10.1016/j.pepi.2021.106823 SN - 0031-9201 SN - 1872-7395 VL - 323 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Blanchard, Ingrid A1 - Petitgirard, Sylvain A1 - Laurenz, Vera A1 - Miyajima, Nobuyoshi A1 - Wilke, Max A1 - Rubie, David C. A1 - Lobanov, Sergey S. A1 - Hennet, Louis A1 - Morgenroth, Wolfgang A1 - Tucoulou, Rémi A1 - Bonino, Valentina A1 - Zhao, Xuchao A1 - Franchi, Ian T1 - Chemical analysis of trace elements at the nanoscale in samples recovered from laser-heated diamond anvil cell experiments JF - Physics and chemistry of minerals N2 - High pressure and high temperature experiments performed with laser-heated diamond anvil cells (LH-DAC) are being extensively used in geosciences to study matter at conditions prevailing in planetary interiors. Due to the size of the apparatus itself, the samples that are produced are extremely small, on the order of few tens of micrometers. There are several ways to analyze the samples and extract physical, chemical or structural information, using either in situ or ex situ methods. In this paper, we compare two nanoprobe techniques, namely nano-XRF and NanoSIMS, that can be used to analyze recovered samples synthetized in a LH-DAC. With these techniques, it is possible to extract the spatial distribution of chemical elements in the samples. We show the results for several standards and discuss the importance of proper calibration for the acquisition of quantifiable results. We used these two nanoprobe techniques to retrieve elemental ratios of dilute species (few tens of ppm) in quenched experimental molten samples relevant for the formation of the iron-rich core of the Earth. We finally discuss the applications of such probes to constrain the partitioning of trace elements between metal and silicate phases, with a focus on moderately siderophile elements, tungsten and molybdenum. KW - NanoSIMS KW - Nano-XRF KW - Diamond anvil cell KW - Focused ion beam Y1 - 2022 U6 - https://doi.org/10.1007/s00269-022-01193-7 SN - 0342-1791 SN - 1432-2021 VL - 49 IS - 6 PB - Springer CY - New York ER - TY - JOUR A1 - Kaa, Johannes M. A1 - Sternemann, Christian A1 - Appel, Karen A1 - Cerantola, Valerio A1 - Preston, Thomas R. A1 - Albers, Christian A1 - Elbers, Mirko A1 - Libon, Lelia A1 - Makita, Mikako A1 - Pelka, Alexander A1 - Petitgirard, Sylvain A1 - Plückthun, Christian A1 - Roddatis, Vladimir A1 - Sahle, Christoph J. A1 - Spiekermann, Georg A1 - Schmidt, Christian A1 - Schreiber, Anja A1 - Sakrowski, Robin A1 - Tolan, Metin A1 - Wilke, Max A1 - Zastrau, Ulf A1 - Konopkova, Zuzana T1 - Structural and electron spin state changes in an x-ray heated iron carbonate system at the Earth's lower mantle pressures JF - Physical review research N2 - The determination of the spin state of iron-bearing compounds at high pressure and temperature is crucial for our understanding of chemical and physical properties of the deep Earth. Studies on the relationship between the coordination of iron and its electronic spin structure in iron-bearing oxides, silicates, carbonates, iron alloys, and other minerals found in the Earth's mantle and core are scarce because of the technical challenges to simultaneously probe the sample at high pressures and temperatures. We used the unique properties of a pulsed and highly brilliant x-ray free electron laser (XFEL) beam at the High Energy Density (HED) instrument of the European XFEL to x-ray heat and probe samples contained in a diamond anvil cell. We heated and probed with the same x-ray pulse train and simultaneously measured x-ray emission and x-ray diffraction of an FeCO3 sample at a pressure of 51 GPa with up to melting temperatures. We collected spin state sensitive Fe K beta(1,3) fluorescence spectra and detected the sample's structural changes via diffraction, observing the inverse volume collapse across the spin transition. During x-ray heating, the carbonate transforms into orthorhombic Fe4C3O12 and iron oxides. Incipient melting was also observed. This approach to collect information about the electronic state and structural changes from samples contained in a diamond anvil cell at melting temperatures and above will considerably improve our understanding of the structure and dynamics of planetary and exoplanetary interiors. Y1 - 2022 U6 - https://doi.org/10.1103/PhysRevResearch.4.033042 SN - 2643-1564 VL - 4 IS - 3 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Schultze, Dina A1 - Wirth, Richard A1 - Wunder, Bernd A1 - Loges, Anselm A1 - Wilke, Max A1 - Franz, Gerhard T1 - Corundum-quartz metastability BT - the influence of a nanometer-sized phase on mineral equilibria in the system Al2O3-SiO2-H2O JF - Contributions to mineralogy and petrology N2 - The metastable paragenesis of corundum and quartz is rare in nature but common in laboratory experiments where according to thermodynamic predictions aluminum-silicate polymorphs should form. We demonstrate here that the existence of a hydrous, silicon-bearing, nanometer-thick layer (called "HSNL") on the corundum surface can explain this metastability in experimental studies without invoking unspecific kinetic inhibition. We investigated experimentally formed corundum reaction products synthesized during hydrothermal and piston-cylinder experiments at 500-800 degrees C and 0.25-1.8 GPa and found that this HSNL formed inside and on the corundum crystals, thereby controlling the growth behavior of its host. The HSNL represents a substitution of Al with Si and H along the basal plane of corundum. Along the interface of corundum and quartz, the HSNL effectively isolates the bulk phases corundum and quartz from each other, thus apparently preventing their reaction to the stable aluminum silicate. High temperatures and prolonged experimental duration lead to recrystallization of corundum including the HSNL and to the formation of quartz + fluid inclusions inside the host crystal. This process reduces the phase boundary area between the bulk phases, thereby providing further opportunity to expand their coexistence. In addition to its small size, its transient nature makes it difficult to detect the HSNL in experiments and even more so in natural samples. Our findings emphasize the potential impact of nanometer-sized phases on geochemical reaction pathways and kinetics under metamorphic conditions in one of the most important chemical systems of the Earth's crust. KW - Experimental KW - Metastability KW - Corundum KW - Quartz KW - Nanolayers KW - Aluminium– silicates Y1 - 2021 U6 - https://doi.org/10.1007/s00410-021-01786-5 SN - 0010-7999 SN - 1432-0967 VL - 176 IS - 4 PB - Springer CY - Berlin ; Heidelberg ER - TY - JOUR A1 - Klemme, Stephan A1 - Feldhaus, Michael A1 - Potapkin, Vasily A1 - Wilke, Max A1 - Borchert, Manuela A1 - Louvel, Marion A1 - Loges, Anselm A1 - Rohrbach, Arno A1 - Weitkamp, Petra A1 - Welter, Edmund A1 - Kokh, Maria A. A1 - Schmidt, Christian A1 - Testemale, Denis T1 - A hydrothermal apparatus for x-ray absorption spectroscopy of hydrothermal fluids at DESY JF - Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques N2 - We present a new autoclave that enables in situ characterization of hydrothermal fluids at high pressures and high temperatures at synchrotron x-ray radiation sources. The autoclave has been specifically designed to enable x-ray absorption spectroscopy in fluids with applications to mineral solubility and element speciation analysis in hydrothermal fluids in complex compositions. However, other applications, such as Raman spectroscopy, in high-pressure fluids are also possible with the autoclave. First experiments were run at pressures between 100 and 600 bars and at temperatures between 25 degrees C and 550 degrees C, and preliminary results on scheelite dissolution in fluids of different compositions show that the autoclave is well suited to study the behavior of ore-forming metals at P-T conditions relevant to the Earth's crust. Y1 - 2021 U6 - https://doi.org/10.1063/5.0044767 SN - 0034-6748 SN - 1089-7623 VL - 92 IS - 6 PB - AIP Publishing CY - Melville ER - TY - JOUR A1 - Krstulović, Marija A1 - Rosa, Angelika D. A1 - Biedermann, Nicole A1 - Irifune, Tetsuo A1 - Wilke, Max T1 - Structural changes in aluminosilicate glasses up to 164 GPa and the role of alkali, alkaline earth cations and alumina in the densification mechanism JF - Chemical geology : official journal of the European Association for Geochemistry N2 - Pressure induced structural changes in silicate melts have a great impact on their physico-chemical properties and hence on their behaviour in the deep Earth's interior. In order to gain a deeper understanding we have studied the densification mechanism in multicomponent aluminosilicate glasses (albitic and albit-diopside composition) by means of extended X-ray absorption fine structure spectroscopy coupled to a diamond anvil cell up to 164 GPa. We have monitored the structural modifications from the network-former Ge as well as the network-modifier Sr. Notably, we tracked the evolution of Ge-O and Sr-O bond lengths (RGe-O, RSr-O) and their coordination number with pressure. We show that RGe-O increases strongly up to about 32 GPa, whereas RSr-O increases only slightly up to similar to 26 GPa. We assign these extensions to the increase of the coordination number from 4 to 6 (Ge) and from similar to 6 to at least 9 (Sr). Upon further compression RGe-O and RSr-O exhibit a continuous decrease to the highest probed pressure. These bond contractions, notably of RGe-O, that are continuous and exceed the one observed in pure SiO2 and GeO2, reflect a higher structural flexibility of multi-component glasses compared to those simple systems. Particularly, the high fraction of non-bridging oxygen atoms due to the presence of Na, Sr, Ca, Mg in the studied glasses, favours the simple compression of the highly-coordinated polyhedra of Si and Ge at pressure greater than 30 GPa. This is in strong contrast to pure oxides where cation polyhedral distortions govern the densification mechanism of the glass. The results of this study demonstrate that low field-strength alkali and alkaline earth cations, ubiquitous in deep Earth's melts, have a profound influence on the densification mechanism of glasses. Our results provide important constrains for interpreting the observed low velocity anomalies at the Earth's core-mantle boundary that have been, beyond others, referred to the presence of high-density melts. The hypothesis that non-buoyant melts at the Earth's core-mantle boundary can be formed by peculiar structural transformations in melts leading to higher coordination numbers compared to their crystalline equivalents is not supported from the present observations. The present results rather suggest that if velocity anomalies are to be explained by melts, these likely have considerable differences in chemical composition to the surrounding crystalline phase assemblage. Y1 - 2020 U6 - https://doi.org/10.1016/j.chemgeo.2020.119980 SN - 0009-2541 SN - 1872-6836 VL - 560 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Cerantola, Valerio A1 - Wilke, Max A1 - Kantor, Innokenty A1 - Ismailova, Leyla A1 - Kupenko, Ilya A1 - McCammon, Catherine A1 - Pascarelli, Sakura A1 - Dubrovinsky, Leonid S. T1 - Experimental investigation of FeCO3 (siderite) stability in Earth's lower mantle using XANES spectroscopy JF - American mineralogist : an international journal of earth and planetary materials N2 - We studied FeCO3 using Fe K-edge X-ray absorption near-edge structure (XANES) spectroscopy at pressures up to 54 GPa and temperatures above 2000 K. First-principles calculations of Fe at the K-edge in FeCO3 were performed to support the interpretation of the XANES spectra. The variation of iron absorption edge features with pressure and temperature in FeCO3 matches well with recently reported observations on FeCO3 at extreme conditions, and provides new insight into the stability of Fe-carbonates in Earth's mantle. Here we show that at conditions of the mid-lower mantle, ~50 GPa and ~2200 K, FeCO3 melts and partially decomposes to high-pressure Fe3O4. Carbon (diamond) and oxygen are also inferred products of the reaction. We constrained the thermodynamic phase boundary between crystalline FeCO3 and melt to be at 51(1) GPa and ~1850 K. We observe that at 54(1) GPa, temperature-induced spin crossover of Fe2+ takes place from low to high spin such that at 1735(100) K, all iron in FeCO3 is in the high-spin state. A comparison between experiment and theory provides a more detailed understanding of FeCO3 decomposition observed in X-ray absorption spectra and helps to explain spectral changes due to pressure-induced spin crossover in FeCO3 at ambient temperature. KW - Deep carbon cycle KW - siderite KW - decomposition KW - melting KW - spin transition KW - Earth in Five Reactions: A Deep Carbon Perspective Y1 - 2019 U6 - https://doi.org/10.2138/am-2019-6428 SN - 0003-004X SN - 1945-3027 VL - 104 IS - 8 SP - 1083 EP - 1091 PB - Mineralogical Society of America CY - Chantilly ER - TY - JOUR A1 - Taran, Michail N. A1 - Nunez Valdez, Maribel A1 - Efthimiopoulos, Ilias A1 - Müller, J. A1 - Reichmann, Hans-Josef A1 - Wilke, Max A1 - Koch-Müller, Monika T1 - Spectroscopic and ab initio studies of the pressure-induced Fe2+ high-spin-to-low-spin electronic transition in natural triphylite-lithiophilite JF - Physics and Chemistry of Minerals N2 - Using optical absorption and Raman spectroscopic measurements, in conjunction with the first-principles calculations, a pressure-induced high-spin (HS)-to-low-spin (LS) state electronic transition of Fe2+ (M2-octahedral site) was resolved around 76-80GPa in a natural triphylite-lithiophilite sample with chemical composition (LiFe0.7082+Mn0.292PO4)-Li-M1-Fe-M2 (theoretical composition (LiFe0.52+Mn0.5PO4)-Li-M1-Fe-M2). The optical absorption spectra at ambient conditions consist of a broad doublet band with two constituents (1) (similar to 9330cm(-1)) and (2) (similar to 7110cm(-1)), resulting from the electronic spin-allowed transition (T2gEg)-T-5-E-5 of octahedral (HSFe2+)-Fe-M2. Both (1) and (2) bands shift non-linearly with pressure to higher energies up to similar to 55GPa. In the optical absorption spectrum measured at similar to 81GPa, the aforementioned HS-related bands disappear, whereas a new broadband with an intensity maximum close to 16,360cm(-1) appears, superimposed on the tail of the high-energy ligand-to-metal O2-Fe2+ charge-transfer absorption edge. We assign this new band to the electronic spin-allowed dd-transition (1)A(1g)(1)T(1g) of LS Fe2+ in octahedral coordination. The high-pressure Raman spectra evidence the Fe2+ HS-to-LS transition mainly from the abrupt shift of the P-O symmetric stretching modes to lower frequencies at similar to 76GPa, the highest pressure achieved in the Raman spectroscopic experiments. Calculations indicated that the presence of Mn-M2(2+) simply shifts the isostructural HS-to-LS transition to higher pressures compared to the triphylite Fe-M2(2+) end-member, in qualitative agreement with our experimental observations. KW - Phosphates KW - Triphylite KW - Raman KW - Infrared KW - Optical absorption spectroscopy KW - High pressure KW - Spin transition KW - DFT Y1 - 2019 U6 - https://doi.org/10.1007/s00269-018-1001-y SN - 0342-1791 SN - 1432-2021 VL - 46 IS - 3 SP - 245 EP - 258 PB - Springer CY - New York ER - TY - JOUR A1 - Petitgirard, Sylvian A1 - Sahle, C. J. A1 - Weis, C. A1 - Gilmore, K. A1 - Spiekermann, Georg A1 - Tse, J. S. A1 - Wilke, Max A1 - Cavallari, C. A1 - Cerantola, V A1 - Sternemann, Christian T1 - Magma properties at deep Earth’s conditions from electronic structure of silica JF - Geochemical perspectives letters N2 - SiO(2 )is the main component of silicate melts and thus controls their network structure and physical properties. The compressibility and viscosities of melts at depth are governed by their short range atomic and electronic structure. We measured the O K-edge and the Si L-2,L-3-edge in silica up to 110 GPa using X-ray Raman scattering spectroscopy, and found a striking match to calculated spectra based on structures from molecular dynamic simulations. Between 20 and 27 GPa, Si-[4] species are converted into a mixture of Si-[5] and Si-[6] species and between 60 and 70 GPa, Si-[6] becomes dominant at the expense of Si-[5] with no further increase up to at least 110 GPa. Coordination higher than 6 is only reached beyond 140 GPa, corroborating results from Brillouin scattering. Network modifying elements in silicate melts may shift this change in coordination to lower pressures and thus magmas could be denser than residual solids at the depth of the core-mantle boundary. Y1 - 2019 U6 - https://doi.org/10.7185/geochemlet.1902 SN - 2410-339X SN - 2410-3403 VL - 9 SP - 32 EP - 37 PB - Association of Geochemistry CY - Paris ER -