Quantification of mineral behavior in four dimensions: Grain boundary and substructure dynamics in salt

Authors

  • V. E. Borthwick,

    1. Department of Geological Sciences, Stockholm University, Svante Arrhenius väg 8C, Stockholm SE-10691, Sweden
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  • S. Schmidt,

    1. Research Division, Risø DTU, Technical University of Denmark, Frederiksborgvej 399, PO Box 49, DK-4000 Roskilde, Denmark
    2. Department of Physics, DTU, Technical University of Denmark, Building 307-309-311-312, DK-2800 Kongens Lyngby, Denmark
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  • S. Piazolo,

    1. Department of Geological Sciences, Stockholm University, Svante Arrhenius väg 8C, Stockholm SE-10691, Sweden
    2. Australian Research Council Centre of Excellence for Core to Crust Fluid Systems/GEMOC National ARC Key Centre, Department of Earth and Planetary Sciences, Macquarie University, New South Wales 2109, Australia
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  • C. Gundlach

    1. European Synchrotron Radiation Facility, 6 Rue Jules Horowitz, F-38043 Grenoble CEDEX 9, France
    2. MaxLab IV, Lund University, PO Box 118, Lund SE-22100, Sweden
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Abstract

[1] Here we present the first four dimensional (time and three dimensional space resolved) experiment on a strongly deformed geological material. Results show that even complicated microstructures with large continuous and discontinuous changes in crystallographic orientation can be resolved quantitatively. The details that can be resolved are unprecedented and therefore the presented technique promises to become influential in a wide range of geoscientific investigations. Grain and subgrain scale processes are fundamental to mineral deformation and associated Earth Dynamics, and time resolved observation of these processes is vital for establishing an in-depth understanding of the latter. However, until recently, in situ experiments were restricted to observations of two dimensional surfaces. We compared experimental results from two dynamic, in situ annealing experiments on a single halite crystal; a 2D experiment conducted inside the scanning electron microscope and a 3D X-ray diffraction experiment. This allowed us to evaluate the possible effects of the free surface on grain and subgrain processes. The extent to which surface effects cause experimental artifacts in 2D studies has long been questioned. Our study shows that, although the nature of recovery processes are the same, the area swept by subgrain boundaries is up to 5 times larger in the volume than observed on the surface. We suggest this discrepancy is due to enhanced drag force on subgrain boundaries by thermal surface grooving. Our results show that while it is problematic to derive absolute mobilities from 2D experiments, derived relative mobilities between boundaries with different misorientation angles can be used.

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