Preprints
https://doi.org/10.5194/se-2021-83
https://doi.org/10.5194/se-2021-83

  21 Jun 2021

21 Jun 2021

Review status: this preprint is currently under review for the journal SE.

Biotite supports long-range diffusive transport in dissolution-precipitation creep in halite

Berit Ina Schwichtenberg1, Florian Fusseis1, Ian B. Butler1, and Edward Andò2 Berit Ina Schwichtenberg et al.
  • 1The University of Edinburgh, Edinburgh, United Kingdom
  • 2Université des Alpes, Grenoble, France

Abstract. Phyllosilicates are generally regarded to have a reinforcing effect on chemical compaction by dissolution-precipitation creep (DPC) and thereby influence the evolution of hydraulic rock properties relevant to groundwater resources, geological repositories as well as fossil fuel reservoirs. We conducted oedometric compaction experiments on layered NaCl-biotite samples to test this assumption. In particular, we aim to analyse slow chemical compaction processes in the presence of biotite on the grain scale and determine the effects of chemical and mechanical feedbacks. We used time-resolved (4D) microtomographic data to capture the dynamic evolution of the transport properties in layered NaCl-NaCl/biotite samples over 1619 and1932 hours of compaction. Percolation analysis in combination with advanced digital volume correlation techniques showed that biotite grains influence the dynamic evolution of porosity in the sample by promoting a reduction of porosity in their vicinity. However, the lack of preferential strain localisation around phyllosilicates and a homogeneous distribution of axial shortening across the sample suggests that the porosity reduction is not achieved by pore collapse but by the precipitation of NaCl sourced from outside the NaCl/biotite layer. Our observations invite a renewed discussion of the effect of phyllosilicates on DPC, with a particular emphasis on the length scales of the processes involved. We propose that, in our experiments, the diffusive transport processes invoked in classical theoretical models of DPC are superseded by chemo-mechanical feedbacks that arise on longer length scales. These feedbacks drive NaCl diffusion from the marginal pure NaCl layers into the central NaCl-biotite mixture over distances of several hundredμm and several grain diameters. Such a mechanism was first postulated by Merino et al. (1983)

Berit Ina Schwichtenberg et al.

Status: open (until 04 Aug 2021)

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Berit Ina Schwichtenberg et al.

Berit Ina Schwichtenberg et al.

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Short summary
Hydraulic rock properties such as porosity and permeability are relevant factors that have an impact on groundwater resources, geological repositories and fossil fuel reservoirs. We investigate the influence of chemical compaction upon the porosity evolution in salt-biotite mixtures and related transport length scales by conducting laboratory experiments in combination with 4D analysis. Our observations invite a renewed discussion of the effect of sheet silicates on chemical compaction.