Biotite supports long-range diffusive transport in dissolution–precipitation creep in halite through small porosity fluctuations

janvier 10, 2022

Berit Schwichtenberg (1), Florian Fusseis (1), Ian B. Butler (1), Edward Andò (2)
Solid Earth. Volume 13, Issue 1 (10 January 2022). DOI: https://doi.org/10.5194/se-13-41-2022


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 and 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 (4-D) microtomographic data to capture the dynamic evolution of the porosity in layered NaCl–NaCl/biotite samples over 1619 and 1932 h 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 complemented 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 hundred micrometres and several grain diameters. Such a mechanism was first postulated by Merino et al. (1983).


How Our Software Was Used

Dragonfly’s Deep Learning Segmentation tool was applied to discretely segment the NaCl. The resulting binarised image stacks were used for image analysis to quantify the porosity evolution and NaCl migration.


Author Affiliation

(1) The University of Edinburgh, School of Geosciences, Edinburgh, UK
(2) Université des Alpes, CRNS, Laboratoire 3SR, Grenoble, France