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Our Research Projects

PUBLICATIONS OF THE RESEARCH GROUPS

DFG

  • Oxidation-induced Weathering of Primary Iron-rich Silicates: Scale-dependent Rates and their Controls
    For the understanding of weathering processes in silicate rocks and soils, the determination of weathering rates and their controls is of great importance. A principal weathering process is the oxidation of Fe(II) in primary Fe-rich silicates. It is generally believed that this process initiates and enhances the weathering of these minerals, as it creates new pathways for weathering agents. Despite the importance of structural Fe(II) oxidation for bedrock weathering and soil formation, comparative bulk and in situ (micro- to nanometer-scale) investigations on oxidation-induced chemical and structural transformations (e.g., cation release, lattice distortion, micro fractures) of primary Fe(II)-bearing silicates during weathering are missing. Therefore, the overall aim of this project is to explore the oxidation-induced weathering of biotite, olivine, and pyroxene at the bulk and in situ scale and to elucidate abiotic controls of this process. Specific objectives are to (1) determine bulk mineral and in situ Fe(II) oxidation and cation-release rates, (2) elucidate the role of low molecular weight organic acid anions and reactive oxygen species (ROS) in oxidative silicate weathering, (3) study oxidation-related structural changes, and (4) explore the spatial extent of in situ Fe(II) oxidation. These objectives will be achieved by performing abiotic flow-through and batch reactor experiments. Bulk mineral dissolution, bulk Fe(II) oxidation, and ROS formation will be assessed by wet-chemical analyses, including inductively coupled plasma-optical emission spectrometry, high-performance liquid chromatography, and UV-Vis spectrophotometry. For in situ analyses, a combination of transmission electron microscopy techniques will be employed (high-resolution imaging, energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy, selected area electron diffraction). In summary, the project will integrate bulk and in situ observations and provide the first comprehensive quantitative information on abiotic oxidative weathering of important primary Fe(II)-bearing silicates. The project will thus contribute to a significant advance in the mechanistic understanding of critical-zone weathering reactions.
    Led by: Dr. Ricarda Behrens
    Year: 2022
    Funding: DFG
    Duration: 2 years
  • Abundance and composition of inorganic X-ray amorphous materials in soils
    "X-ray amorphous" solids are characterized by extremely small crystal sizes, pronounced lattice distortions or atomic short-range order. In comparison to crystalline solids, "X-ray amorphous" solids possess diffuse X-ray diffraction patterns and thus remain "visible" as elevated signal background in X-ray diffractograms. In soils, inorganic X-ray amorphous materials (iXAMs) exist as vitreous phases, minerals whose crystals have too few repeating structural units to diffract X-rays ("poorly crystalline" or "nanocrystalline" minerals), and solids of variable chemical composition possessing exclusively atomic short-range order ("mineraloids"). Due to their large specific surface areas and reactive surface groups, iXAMs control important soil processes such as carbon turnover, mineral weathering, and sorption reactions of nutrients and pollutants. Despite their ecological significance, soil iXAMs are still poorly understood. Knowledge gaps exist particularly with regard to their nature, total contents, chemical composition, and distribution in soils as well as their quantifiability using wet chemical extraction methods. To fill these knowledge gaps, we quantify iXAMs in the fine earth (<2 mm) and in particle-size fractions of four soil types (Cambisol, Chernozem, Luvisol, Podsol) by quantitative X-ray diffraction (Rietveld method). The chemical composition of the iXAMs is determined by mass balances based on the Rietveld results and chemical analyses of the soil samples ("balance sheet method"). On this basis, we investigate the suitability of common selective extraction methods for the determination of "X-ray amorphous" soil solids to quantitatively determine their absolute contents and chemical composition in soils. In addition, we explore the nature and composition of iXAMs (<1 µm) from selected particle-size fractions using analytical transmission electron microscopy. Overall, the research project provides basic information (1) on total iXAM contents in soils, their nature and chemical composition as well as depth-dependent distribution and (2) on the quantification of iXAMs by selective extraction methods. Thus, this project forms the basis for a detailed investigation of the influence of iXAMs on soil functions and properties in the future.
    Led by: Professor Dr. Christian Mikutta (LUH), Dr. Reiner Dohrmann (BGR)
    Team: M. Sc. Sileola Joseph Akinbodunse
    Year: 2021
    Funding: DFG
    Duration: 2021-2023
  • The mafic magma plumbing system in the Snake River Plain Province (Yellowstone hotspot, USA): Contribution from the analysis of crystal cargoes and melt inclusions in basaltic lavas from the Kimama drilling core.
    The ICDP drilling in the Snake River Plain (SRP) volcanic province (western United States) was aimed at understanding the interaction of a hotspot with the continental lithosphere. This understanding requires information on the evolution of chemistry, sources, differentiation and storage conditions of both the rhyolitic and basaltic magmas that have been produced over the last 17 Ma years.The major objective of this project is to construct a model of magma plumbing system for the Snake River Plain (SRP) mafic to intermediate magmas. Using the information provided by the crystal cargoes in basaltic volcanic rocks from the Kimama ICDP bore hole (~ 1800 meters of more than 500 basaltic lava flows) the storage conditions of magma reservoirs, magma ascent pathways and transcrustal magmatic processes will be described. We will achieve this by coupling two types of investigations: 1) by linking textural and compositional information from zoned crystals and 2) by the analysis of the composition of re-homogenized melt inclusions in the mineral phases. The originality of the approach is the combination of the detailed analysis of different types of mineral phases (olivine, plagioclase, clinopyroxene and spinel) together with the analysis of melt inclusions in those minerals. Thermobarometric constraints and the origin of compositional zoning (e.g., textures related to different magmatic processes such as decompression melting, magma replenishment or convective processes) will be used to identify different populations of crystals and different magmatic environments. When present, diffusion profiles will be used to constrain time scales of magmatic processes (e.g., time that a crystal spent in a specific reservoir or environment).Since all basalts have a partially or fully crystallized groundmass, the composition of melts coexisting with the crystal cargo will be determined from re-homogenized glass inclusions. Re-homogenization will be performed at realistic temperatures (~ 1100 -1200 °C) in high pressure vessels (up to 500 MPa) which is necessary to avoid diffusive transfer of volatiles (mainly water) out of the inclusions (at least for olivine). The analysis of re-homogenized inclusions will provide the possibility to reconstruct the composition of melts (major elements, trace elements, amount of volatiles), to trace the melt compositions in the different environments, and to discuss the differentiation processes (as a complement to mineral compositions, see above). Using solubility models of H2O and CO2 in silicate melts, the estimations of volatile contents (H2O and CO2) will provide an additional tool to constrain the pressure of entrapment and will complement the thermobarometric information. Since primitive undifferentiated basaltic samples are not represented in the SRP, the major and trace element analysis of glass inclusions in olivine may also be useful to characterize the geochemical signature of the source region.
    Led by: Professor Dr. Francois Holtz, Ph.D.
    Team: Dr. Clara Waelkens
    Year: 2021
    Funding: DFG
    Duration: 2021-2023
  • Carbon recycling by arc magmatism: an assessment from experimentally homogenized melt inclusions in olivine
    Led by: Prof. Dr. Francois, Holtz(LUH), Prof. Dr. Roman Botcharnikov (Johannes Gutenberg-Universität Mainz)
    Team: M.Sc. Stepan Petrovich Krashenninnikov
    Year: 2020
    Funding: DFG
    Duration: 2020-2023
  • Understanding the crust-mantle transition from fast-spreading mid-ocean ridges: experiments and analytical studies using ICDP OmanDP drill core samples
    Led by: Prof. Dr. Francois Holtz, Prof. Dr. Jürgen Koepke (LUH), Dr. Carl-Dieter Garbe-Schönberg (Christian-Albrechts-Universität zu Kiel)
    Year: 2020
    Funding: DFG
    Duration: 2020-2023
  • "Rare-metal enrichment in carbonatite-bearing magmatic systems: Part B. Understanding the role of fractional crystallization and liquid immiscibility by experimental simulations of silicate-carbonatite systems" as part of the priority programm "SPP 2238:
    Led by: Prof. Dr. Francois Holtz (LUH), Prof. Dr. Roman Botcharnikov (Johannes Gutenberg-Universität Mainz), Prof. Dr. Marion Tichomir (Technische Universität Bergakademie Freiberg)
    Team: M. Sc. Antonia Simon
    Year: 2020
    Funding: DFG
    Duration: 3 years
  • Transport and reactions of light elements (Li, B) in pegmatitic systems under thermal disequilibrium - implications for magmatic/hydrothermal ore deposits
    Led by: Prof. Dr. Harald Behrens, Prof. Dr. Stefan Weyer
    Team: M. Sc. Christian Ronny Singer
    Year: 2020
    Funding: DFG
    Duration: 2020-2023
  • Chronometry in plutonic rocks: cooling rates of ancient oceanic crust
    Led by: Dr. Maria Kirchenbaur (LUH), Dr. Kathrin Faak (Ruhr-Universität Bochum )
    Year: 2020
    Funding: DFG
    Duration: 3 Jahre
  • Diffusion-driven Fe-Mg and Li isotope fractionation in olivine: An experimental investigation and new modeling approach
    In this project of the proposed research unit, we aim to experimentally investigate isotope fractionation in magmatic crystals, generated by chemical diffusion. In the first funding period, we aim to focus on olivine and Fe and Mg isotope fractionation, driven by Fe-Mg exchange diffusion, as well as diffusion-driven Li isotope fractionation. In a second funding period such investigations may be extended to other magmatic minerals, such as pyroxene and plagioclase, for which the diffusion rate will be investigated in other projects (# 1 and #2) of the research unit, during the first funding period.The use of isotopic zoning has recently been developed as an additional complementary tool in diffusion chronology, including Fe-Mg and Li isotope zoning in olivine. The advantage of isotopes is that at magmatic temperatures isotopes only significantly fractionate during diffusion, while equilibrium isotope fractionation is small. Isotopic zoning can thus be used to unequivocally identify diffusion-driven zoning and furthermore, in combination with chemical zoning to resolve complex magmatic scenarios in which magmatic crystals experienced several growth and diffusion stages. However, the extend of diffusion-driven isotopic zoning is yet barely known and isotopic profiles observed in natural olivines are only fitted to assumed models of isotopic fractionation during diffusion modelling. We propose the precise experimental determination of diffusion-driven isotope fractionation and its dependence on parameters such as temperature, oxygen fugacity, chemical composition and crystallographic orientation of the olivine. This will result in much better constraints on the initial boundary conditions that are assumed for the diffusion model, and consequently lead to the determination of more accurate constraints on the duration of magmatic processes. It will also help to improve estimates of diffusion-driven chemical fluxes (during partial melting or metasomatic events), based on mineral- or even bulk rock isotopic data.We will furthermore develop 3D models to predict the anisotropy of isotope fractionation profiles that should allow to identify sectioning effects in natural crystals zoning. This model and all findings on diffusion-driven isotope fractionation will be implemented into the user friendly software for diffusion modelling, which will be developed in project #6. In cooperation with project #8, we will already apply the experimentally calibrated isotope zoning, as determined in this project, for the investigation of natural olivine.
    Led by: Prof. Dr. Stefan Weyer (LUH), Dr. Ralf Dohmen (RUB)
    Team: Dr. Martin Oeser-Rabe
    Year: 2020
    Funding: DFG
    Duration: 2020-2023
  • Chronometry in plutonic rocks: cooling rates of ancient oceanic crust
    Since the onset of plate tectonics the formation of new oceanic crust at mid-ocean ridges is a principal mechanism of cooling of the Earth's interior. However, one of the central unsolved problems is how heat is efficiently transferred during the formation of the plutonic section of the oceanic crust. Several models for the generation of the plutonic section of oceanic ridges have been put forward, which mainly revolve around cooling of the oceanic crust by conduction vs. advection of fluids through the crust. Prominent end-member models include the gabbro-glacier model and the sheeted sill model. Attempts to test the models have led to inconclusive results so far. For example, while evidence of deep hydrothermal flow is found in the rocks, cooling of the overall crust appears to be more compatible with conductive cooling. Therefore, it is necessary to map out the distribution of cooling rates as a function of distance from documented fluid pathways, while simultaneously quantifying the fluid flux. We propose to address this problem with a comprehensive, multiscale approach, combining diffusion chronometry and isotope geochemistry on samples from focused fluid flow zones (FFFZ) within the layered gabbros of the Wadi Gideah reference profile in the Oman ophiolite. If such zones have the potential for an effective cooling of the deep crust, we expect strong cooling of layered gabbros at the contact of the FFFZs. Moreover, if such fluid flow is capable of enhancing the cooling rate of the surrounding crust as a whole, such high cooling rates would be recorded even in the far field region with respect to the FFFZ. Alternatively, if high cooling rates are obtained only in the near-field region, it may explain why signatures of conductive cooling for the crust as a whole are obtained even when evidence of fluid flow is present.Therefore, we aim to quantify cooling rates in multiple profiles beginning at the contact to a FFFZ and progressing away into the massive layered gabbro. Cooling rates will be determined on olivine, plagioclase and pyroxenes in various gabbro samples using multiple diffusion chronometers. These include, for example, the well-established Ca-in-olivine geospeedometer together with the recently developed geospeedometers based on trace element diffusion in plagioclase (Mg, Ba, Sr, La, Ce) as well as any possible chronometers using pyroxenes (e.g. Fe-Mg, Sr or Li diffusion in clinopyroxene). Additionally, we propose to apply the fast-diffusing stable Li isotope system, which is a highly suitable tool for the determination of hydrothermally promoted fast cooling rates in the system olivine-pyroxene-plagioclase and can as such be used to simultaneously determine cooling rates as well as fluid fluxes. In addition to providing insights into the cooling mechanism of the oceanic crust, the study would enable us to check the consistency and robustness of different diffusion chronometers applied on the same samples.
    Led by: Dr. Kathrin Faak (Ruhr-Universität Bochum), Dr. Maria Kirchenbaur (LUH)
    Team: Dr. Kathrin Faak (Ruhr-Universität Bochum), Dr. Maria Kirchenbaur (LUH)
    Year: 2020
    Funding: DFG
    Duration: 2021-2024
  • New insights into the interplay between water diffusion and viscosity in magma fragmentation
    Led by: Prof. Dr. Harald Behrens
    Team: M. Sc. Florian Pohl
    Year: 2019
    Funding: DFG
    Duration: 2019-2020
  • Interactions between manganese oxides and dissolved organic matter in soil
    Led by: Prof. Dr. Christian Mikutta, Dr. Ricarda Behrens (Leibniz Universität Hannover), Robert Mikutta, Klaus Kaiser (Martin-Luther-Universität Halle-Wittenberg)
    Team: M. Sc. Lena Brüggenwirth
    Year: 2019
    Funding: DFG
    Duration: 2019-2022
  • Auswirkung der Schneidkanteneigenspannungen auf das Verschleißverhalten PVD-beschichteter Zerspanwerkzeuge
    Residual stresses in hard material layers have a large influence on the tool life. Measurement at the cutting edge is not possible with the established methods. Raman spectroscopy shows high potential for this measurement task. The measurement method is calibrated by X-ray diffraction in the scattering vector mode.
    Led by: Prof. Breidenstein, Bernd (breidenstein@ifw.uni-hannover.de), Prof. Behrens, Harald (h.behrens@mineralogie.uni-hannover.de)
    Team: Dipl.-Geow. Marcel Dietrich, m.dietrich@mineralogie.uni-hannover.de
    Year: 2018
    Funding: DFG
    Duration: 2018-2020
  • Reconstruction of Seawater Carbonate chemistry during the last Glacial-Interglacial transition from Boron isotopic ratios and concentrations in foraminifera
    Led by: Dr. Ingo Horn, Prof. Dr. Jelle Bijma, Alfred-Wegener-Institut Bremerhaven
    Team: Dr. Markus Raitzsch
    Year: 2016
    Funding: DFG
    Duration: 2016-2021
  • Differentiation processes in magma chambers – convective vs. diffusive crystal dissolution
    [Translate to Englisch:]
    Led by: Prof. Behrens H.
    Team: Quetscher A.
    Year: 2012
    Funding: DFG
    Duration: 3 Jahre

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