TY - JOUR A1 - Wilke, Max T1 - Fe in magma : an overview N2 - The strong influence of physical conditions during magma formation on Fe equilibria offers a large variety of possibilities to deduce these conditions from Fe-bearing phases and phase assemblages found in magmatic rocks. Conditions of magma genesis and their evolution are of major interest for the understanding of volcanic eruptions. A brief overview on the most common methods used is given together with potential problems and limitations. Fe equilibria are not only sensitive to changes in intensive parameters (especially T and fO(2)) and extensive parameters like composition also have major effects, so that direct application of experimentally calibrated equilibria to natural systems is not always possible. Best estimates for pre-eruptive conditions are certainly achieved by studies that relate field observations directly to experimental observations for the composition of interest using as many constraints as possible (phase stability relations, Fe-Ti oxides, Fe partitioning between phases, Fe oxidation state in glass etc.). Local structural environment of Fe in silicate melts is an important parameter that is needed to understand the relationship between melt transport properties and melt structure. Assignment of Fe co-ordination and its relationship to the oxidation state seems not to be straightforward. In addition, there is considerable evidence that the co- ordination of Fe in glass differs from that in the melt, which has to be taken into account when linking melt structure to physical properties of silicate melts at T and P. Y1 - 2005 ER - TY - JOUR A1 - Nabelek, Peter I. A1 - Labotka, Theodore C. A1 - Helms, Thomas S. A1 - Wilke, Max T1 - Fluid-mediated mineral consumption and growth in polymetamorphosed metapelites of the Black Hills, South Dakota Y1 - 2005 SN - 0016-7037 ER - TY - THES A1 - Wilke, Max T1 - Untersuchungen zur Eisenspeziation in Mineralphasen unter besonderer Berücksichtigung der Röntgenabsorptionsspektroskopie (XAFS) Y1 - 2006 CY - Potsdam ER - TY - JOUR A1 - Wilke, Max A1 - Appel, Karen A1 - Vincze, Laszlo A1 - Schmidt, Christian A1 - Borchert, Manuela A1 - Pascarelli, Sakura T1 - A confocal set-up for micro-XRF and XAFS experiments using diamond-anvil cells N2 - A confocal set-up is presented that improves micro-XRF and XAFS experiment with high-pressure e diamond-anvil cells (DACs) In this experiment a probing volume is defined by the focus of the incoming synchrotron radiation beam and that of a polycapillary X-ray half-lens with a very long working distance, which is placed in front of the fluorescence detector This set-up enhances the quality of the fluorescence and XAFS spectra, and thus the sensitivity for detecting elements at low concentrations. It efficiently suppresses signal from outside the sample chamber, which stems from elastic and inelastic scattering of the incoming beam by the diamond anvils as well as from excitation of fluorescence from the body of the DAC Y1 - 2010 UR - http://journals.iucr.org/s/journalhomepage.html U6 - https://doi.org/10.1107/S0909049510023654 SN - 0909-0495 ER - TY - JOUR A1 - Nabelek, Peter I. A1 - Labotka, Theodore C. A1 - Helms, Thomas S. A1 - Wilke, Max T1 - Fluid-mediated polymetamorphism related to proterozoic collision of Archean Wyoming and Superior Provinces in the Black Hills, South Dakota Y1 - 2006 ER - TY - JOUR A1 - Wilke, Max A1 - Schmidt, Christian A1 - Farges, Francois A1 - Malavergne, Valerie A1 - Gautron, Laurent A1 - Simionovici, Alexandre A1 - Hahn, Matthias A1 - Petit, Pierre-Emanuel T1 - Structural environment of iron in hydrous aluminosilicate glass and melt-evidence from X-ray absorption spectroscopy N2 - The iron speciation in hydrous haplotonalitic and haplogranitic silicate glasses was studied using XAFS spectroscopy and transmission electron microscopy (TEM). Spectral features occurring at the main crest of the XANES at the iron K-edge of hydrous glasses indicate contributions to the spectra by iron-moieties present in a more ordered structural environment than found in the dry glass. These differences are also suggested by analysis of the EXAFS. These effects are not completely suppressed even for those samples that were quenched with a higher cooling rate. Strongest differences to the dry glass are observed for a sample that was quenched slowly through the temperature of glass transformation. Crystals (60 to 1500 nm in size) of magnetite, maghemite and another unidentified phase were observed in this sample by TEM, whereas no crystals were found in samples quenched with regular or high cooling rates. In-situ XANES measurements up to 700 degrees C and 500 MPa were performed to reveal the origin (i.e., during synthesis or quench) of the structural differences for those hydrous glasses that do not display any detectable crystallization. The comparison of XANES spectra collected on Fe2+ in water-saturated haplogranitic melt at 700 degrees C and 500 MPa and on Fe2+ in dry melt at 1150 degrees C shows that the local structural environment of Fe2+ in both systems is similar. This indicates that there is no detectable and direct influence of water on the local structure around iron in this type of melt. Hence, the differences observed between hydrous and dry glasses can only be related to artefacts formed during the quench process. (c) 2006 Elsevier B.V. All rights reserved Y1 - 2006 U6 - https://doi.org/10.1016/j.chemgeo.2006.01.017 ER - TY - JOUR A1 - Wilke, Max A1 - Partzsch, G. M. A1 - Welter, E. A1 - Farges, Francois T1 - Redox Reaction In Silicate Melts Monitored By Static In-Situ Fe K-edge XANES Up To 1180 C Y1 - 2007 ER - TY - JOUR A1 - Wilke, Max A1 - Farges, Francois A1 - Partzsch, G. M. A1 - Schmidt, C. A1 - Behrens, Harald T1 - Speciation of Fe in silicate glasses and melts by in-situ XANES spectroscopy Y1 - 2007 ER - TY - JOUR A1 - Farges, Francois A1 - de Wispelaere, S. A1 - Rossano, Stephanie A1 - Munoz, Manuel A1 - Wilke, Max A1 - Flank, Anne-Marie A1 - Lagarde, Pierre T1 - Local structures around Si, Al, and Na in hydrated silicate glasses Y1 - 2008 ER -