The availability of synchrotron radiation for research in geoscience opens new experimental possibilities by overcoming the former limitations such as detection limit and spatial resolution. Our group uses a broad energetic range of synchrotron radiation from high-energetic X-rays down to low-energetic infrared radiation for research mostly in-situ at high pressures. The very high brilliance X-rays available at the modern synchrotron sources, such as PETRA III at DESY in Hamburg, allows us to determine (by measuring X-ray diffraction, XRD) the compression behavior of geomaterials up to very high pressures relevant for the deep interior of the Earth.
Examples of in-situ X-ray diffraction in combination with the Multi-Anvil Press:
The P-T conditions of the transition of the silica polymorphs coesite (Coe) – stishovite (Sti) have been investigated in numerous experimental studies in the pure SiO2-system (e.g., Ono et al., 2017). However, Coe and Sti can incorporate significant amounts of Al and H in their structures by various substitution mechanisms. In this project we examine the influence of Al2O3 and H2O on the position of the Coe-Sti transition at P and T using the multi-anvil press at the synchrotron PETRA III, Hamburg, combined with in situ X‑ray diffraction measurements. As starting material, we use 100 % Sti which was formed in situ at 9 GPa and 900 °C prior to our equilibrium experiments from a mixture of amorphous SiO2 plus 1 wt % γ-Al2O3 plus 10 wt % H2O (filled in X-ray transparent Titanium-capsules).
Contact
Dr. Christian Lathe
Dr. Bernd Wunder
Prof. Monika Koch-Müller (Gast)
Partner
Dr. Robert Farla, Deutsches Elektronen-Synchrotron DESY, PETRA III Extension
The presence of water in the earth's crust and mantle has enormous effects on geodynamic processes, because the incorporated hydrogen changes the physical properties of the minerals such as the melting point, rheological behavior (hydrolytical weakening) and the transformation kinetics. Besides in nominally hydrous minerals such as amphibole, serpentine and talc, hydrogen may be stored in nominally anhydrous minerals (NAMs) such as coesite, pyroxene, garnet and olivine. The hydrogen in these minerals is structurally bound as point defects. An appropriate method for detecting traces of hydrogen in minerals is IR spectroscopy. However, Transmission electron microscope analyses of olivine (Khisina et al., 2001) and clinopyroxene (Koch-Müller et al., 2004) showed that the presence of nm-sized hydrous phase inclusions might influence the IR-spectra. Consequently, the amount of hydrogen solved in the crystal structure will be overestimated. Therefore, for correct interpretation of IR-spectra knowledge of the microstructure of the investigated grains is required.
Currently we investigate the incorporation mechanism and solubility of hydrogen into the following nominally anhydrous minerals:
olivine, pyroxene, garnet, kyanite, coesite, stishovite.
We apply transmission electron microscopy to check for nm-sized inclusions. To get insight into the location of hydrogen in the structure we apply linear polarized conventional as well as synchrotron IR radiation (Bessy II) at ambient condition and in-situ as a function of pressure and/or temperature.
Contacts
Dr. Bernd Wunder
Prof. Monika Koch-Müller
Partner
Dr. Ulrich Schade, Helmholtz Zentrum Berlin, Institut Methoden der Materialentwicklung
Breakdown of lawsonite to garnet, kyanite, coesite and H2O: kinetics, reaction mechanism, P/T stability
Lawsonite (CaAl2Si2O7(OH)2·H2O) is an important rockforming mineral containing 11.5 wt% H2O in its crystal structure. It occurs in blueschists and eclogites and therefore its dehydration plays an important role in subduction slabs. The most important dehydration reaction of lawsonite is its breakdown to garnet, kyanite, coesite and H2O in the pressure/temperature ranges 4 – 8 GPa/800 – 1000°C. However, the location of the reaction in the P/T space is not well constrained because of the limited dataset available in this range. Thus, the aim of this study is to fill these gaps in our knowledge by performing HP/HT experiments using the multi-anvil press at the synchrotron PETRA III, Hamburg, combined with in situ X‑ray diffraction measurements. Starting material is very pure natural lawsonite filled with water in excess into X-ray transparent Ti-capsules.
Contact
Prof. Monika Koch-Müller
Dr. Christian Lathe
Partner
Dr. Melanie Sieber, Universität Potsdam
Dr. Robert Farla, Deutsches Elektronen-Synchrotron DESY, PETRA III Extension
Experimental studies have shown that a number of dense hydrous silicates are stable at mantle pressures, corresponding to depths greater than 200 km: e.g. phase A, phase B, phase E, superhydrous phase B, phase Egg. If present in the Earth’s mantle these minerals are important hosts for H2O and their dehydration at much higher P and T may be responsible for deep focus earthquakes. To understand the Earth’s water cycle it is important to learn more about their stabilities and phase relations at P and T (e. g., dehydration reactions).
Contact
Dr. Bernd Wunder
Dr. Christian Lathe
Dr. Sergio Speziale
Prof. Monika Koch-Müller
Partner
Prof. Mainak Mookherjee, Florida State University, Tallahassee
Prof. Mark David Welch, The Natural History Museum, London
Dr. Hanns-Peter Liermann, Deutsches Elektronen-Synchrotron DESY, Hamburg
We investigate the melting behaviour of carbonates in the system CaCO3-MgCO3 at 6 and 9 GPa and high temperature in the Multi-Anvil press. We use the rocking mode of the press to determine the phase relations during melting of carbonates at the Mg-rich side of the system CaCO3-MgCO3 in the absence and in the presence of H2O. Previous studies report tremendous quenching problems as primary grown carbonates could not be distinguished from the quenched melt. We equilibrate the system at 6 GPa and T over six hours by continuously rocking the whole press and let the carbonates swim and grow in the melt. However, shortly before quenching the temperature we stopp the rotation and thus could separate the crystals from the melt as they sank down. Compared to the results of static experiments the corresponding phase diagram is significantly different.
Contact
Prof. Monika Koch-Müller
Dr. Hans Josef Reichmann
Partner
Dr. Melanie Sieber, Universität Potsdam
Dr. Robert Farla, Deutsches Elektronen-Synchrotron DESY, Hamburg
Funding
DFG, GFZ
Seismic observations indicate the presence of seismic anisotropy in several regions of the Earth’s upper and lower mantle. Seismic anisotropy is most likely caused by either crystallographic or shape preferred orientations of mantle phases, which in turn are caused by dynamic mass transport processes. The combination of laboratory constraints and seismic observations are, therefore, a promising avenue to unravel the dynamics of the deep Earth.
Deformation and Microtextures development in lower mantle materials
We are producing microstructures and crystallographic preferred orientation (CPO) in binary mixtures of perovskite and ferropericlase at relevant conditions of the lower mantle in a heated diamond-anvil cell. In-situ characterization using both axial and radial synchrotron x-ray diffraction in combination with ex-situ electron microscopy analyses allows for understanding the stress/strain-behavior in a typical lower mantle assemblage and its implications for seismic anisotropy observations and transport properties in the lower mantle.
Contact
Dr. Sergio Speziale
Dr. Hans Josef Reichmann
Partner
Dr. Hanns-Peter Liermann, Deutsches Elektronen-Synchrotron (DESY) Hamburg
Prof. Lowell M. Miyagi, Montana State University