Chemistry dependence of the grain boundary character distribution (GBCD) of olivine

• Applicant: Dr. Marcel Thielmann, since 12/2018
• Subject Area: Mineralogy, Petrology and Geochemistry ; Physical Chemistry of Solids and Surfaces, Material Characterisation ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2016 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 321722160

• Final Report Year: 2021

Final Report Abstract

Generally, a better understanding of processes occurring at the grain scale is necessary for increased confidence in extrapolating from the lab to Earth, and therefore will improve knowledge of large-scale geodynamic process and interpretations of geophysical observations such as electrical conductivity and seismic anisotropy. We studied the distribution of the grain boundary character and its evolution during experimental deformation and their role in deformation in the dislocation-accommodated grain-boundary sliding (DisGBS) regime. Previous studies suggest that DisGBS is the main deformation mechanism for olivine in most of Earth’s upper mantle. We used electron backscattered diffraction and transmission electron microscopy data to investigate the micromechanics involved in DisGBS, with a focus on the interactions between dislocations and grain boundaries. These interactions in minerals are to date only poorly understood and not yet quantitatively investigated in olivine. The results presented here suggest that grain boundaries play a major role in moderating deformation in the disGBS regime. We present evidence that the rate of deformation is influenced by assimilation of dislocations into grain boundaries and show that dynamic deformation in this specific zsenario creates specific grain boundaries, which evolve as deformation progresses. The effective contribution of grain-boundary processes on the rheology of the upper mantle is correlated to the amount of grain boundaries in upper mantle rocks, that is, their grain-size distribution and evolution. The grain- size distribution in the Earth’s mantle is controlled by the balance between damage (recrystallization under a stress field) and healing (grain growth) processes. However, grain growth, one of the main processes controlling grain size, is still poorly constrained for olivine at conditions of the upper mantle. Experimental data on grain growth kinetics of olivine is to date restricted to pressures of up to 1.2 GPa. To evaluate the effects of pressure on grain growth of olivine, we performed grain growth experiments at pressures ranging from 1 to 12 GPa using piston-cylinder and multi-anvil apparatuses. We found that the olivine grain growth rate is reduced as pressure increases. The results presented here suggest that grain-boundary diffusion is the main process behind grain growth at high pressure. Our results indicate that under deep upper-mantle conditions (depths of 200-400 km), the effect of pressure on inhibiting grain growth counteracts the effect of increasing temperature with increasing depth. Our resluts indicate that the viscosity is approximately constant at the deep upper mantle conditions and are in good agreement with geophysical observations that suggest viscosities on the order of 1021 Pa∙s at the deep upper mantle. Beyond the envisioned outcome of the project our work initiated further ongoing studies: (i) Thermal fracturing during material up-rise in the Earth mantle. (ii) How do grain boundaries mediate deformation? Bicrystal deformation studies. (iii) What is the viscosity of a grain boundary? Bicrystal grain boundary sliding studies.

Publications

• (2017) Quantitative electron backscatter diffraction (EBSD) data analyses using the dictionary indexing (DI) approach: Overcoming indexing difficulties on geological materials. Am. Mineral. 102, 1843–1855
  Marquardt, K. et al.
  
• (2018) A transmission x-ray microscopy and NEXAFS approach for studying corroded silicate glasses at the nanometre scale. Phys. Chem. Glas. 59, 11–26
  Kutzschbach M., Guttmann P., Marquardt K., Werner S., Henzler K. D. and Wilke M.
  
• (2018) Mg lattice diffusion in iron-free olivine and implications to conductivity anomaly in the oceanic asthenosphere. Earth Planet. Sci. Lett. 484, 204–212
  Fei H., Koizumi S., Sakamoto N., Hashiguchi M., Yurimoto H., Marquardt K., Miyajima N. and Katsura T.
  
• (2018) Seismically invisible water in Earth’s transition zone? Earth Planet. Sci. Lett. 498, 9–16
  Schulze K., Marquardt H., Kawazoe T., Boffa Ballaran T., McCammon C., Koch-Müller M., Kurnosov A. and Marquardt K.
  
• (2018) The structure and composition of olivine grain boundaries: 40 years of studies, status and current developments. Phys. Chem. Miner. 45, 139–17
  Marquardt, K. & Faul, U. H.
  
• (2018) Weathering of Bibearing tennantite. Chem. Geol. 499, 1–25
  Keim M. F., Staude S., Marquardt K., Bachmann K., Opitz J. and Markl G.
  
• (2019) Intragranular plasticity vs. grain boundary sliding (GBS) in forsterite: Microstructural evidence at high pressures (3.5–5.0 GPa). Am. Mineral. 104, 220–231
  Bollinger, C., Marquardt, K. & Ferreira, F.
  
• (2019) Lead diffusion in CaTiO3: A combined study using Rutherford backscattering and TOF-SIMS for depth profiling to reveal the role of lattice strain in diffusion processes. Am. Mineral. 104, 557–568
  Beyer, C., Dohmen, R. Rogalla, D.; Becker, H.-W., Marquardt, K.; Vollmer, Chr.
  
• (2020) Evidence for complex iron oxides in the deep mantle from FeNi(Cu) inclusions in superdeep diamond
  Anzolini C., Marquardt K., Stagno V., Bindi L., Frost D. J., Pearson D. G., Harris J. W., Hemley R. J. and Nestola F.
  
• (2020) Role of inclination dependence of grain boundary energy on the microstructure evolution during grain growth. Acta Mater. 188, 641–651
  Salama H., Kundin J., Shchyglo O., Mohles V., Marquardt K. and Steinbach I.
  
• (2021). Grain boundary diffusion and its relation to segregation of multiple elements in Yttrium Aluminum Garnet
  Polednia, J., Dohmen, R., Marquardt, K.