To D or not to D: Re-evaluating the Role of Constrained Comminution in Cataclastic Deformation
Abstract
Cataclasis is a fundamental mechanical mechanism shaping fault-rock evolution which describes fracturing and particle size reduction during sliding along a fault interface. This process is recorded in part by the evolution of particle size distributions with continued slip, and controls fault-rock porosity, permeability, frictional resistance to sliding, and the formation of new surface area (which consumes a portion of the earthquake energy budget). Thus, mechanistic models of cataclastic deformation are essential for understanding the evolution of fault rocks in the brittle crust. The most accepted model for cataclasis is "constrained comminution", which predicts a power-law (fractal) distribution of grain sizes described by a scaling factor D. These D-values are routinely used to describe the evolution of particle size distributions with increasing strain. In this contribution, we test for the presence of power-law scaling in ~50 samples from previously published naturally and experimentally deformed fault rocks, thereby assessing the validity of the constrained comminution model. We employ a well-established statistical approach which determines a best-fit power-law function for a particular data set, and then compares that fit to other possible distributions. We find that power-law distributions are a poor fit to each data set. Thus, the examined fault rocks are not consistent with having formed through constrained comminution. Log-normal and stretched exponential distributions are generally a better fit to each data set. We examine possible mechanisms that could produce these alternative distributions, including the density of internal flaws and preferential fracturing of larger grains (protected fines), and discuss how these particle size distributions may evolve with increasing strain.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR44A..08P
- Keywords:
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- 5112 Microstructure;
- PHYSICAL PROPERTIES OF ROCKS;
- 7209 Earthquake dynamics;
- SEISMOLOGY;
- 8034 Rheology and friction of fault zones;
- STRUCTURAL GEOLOGY;
- 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICS