Formation of Nanocrystalline and Amorphous Materials Causes Parallel Brittle‐Viscous Flow of Crustal Rocks: Experiments on Quartz‐Feldspar Aggregates
Name
Pec_AlNasser_JGR.pdf
Description
Submitted version
Size
5.47 MB
Format
Adobe PDF
Checksum (MD5)
08fd2734ac934b176396f10853a2a193
Author(s)
Pec, Matej
Al Nasser, Saleh Mohammed
Date Issued
May 2021
Journal
Journal of Geophysical Research: Solid Earth
Publisher
American Geophysical Union (AGU)
Citation
Pec, Matej and Saleh Al Nasser. "Formation of nanocrystalline and amorphous materials causes parallel brittle-viscous flow of crustal rocks: Experiments on quartz-feldspar aggregates." Journal of Geophysical Research: Solid Earth 126, 5 (May 2021): e2020JB021262. © 2021 American Geophysical Union
Version
Original manuscript
Abstract
The brittle-viscous transition in the lithosphere occurs in a region where many large earthquakes nucleate. To study this transition, we sheared bimineralic aggregates with varying ratio of quartz and potassium feldspar. We deformed the samples in a solid-medium deformation apparatus at temperature, T = 750°C and pressure, Pc = 800 MPa under either constant displacement rate or constant load boundary conditions. Under constant displacement rate, samples reach high shear stress (τ = 0.4–1 GPa depending on mineral ratio) and then weaken. Under constant load, the strain rate shows low sensitivity to stress below τ ≈ 400 MPa, followed by a higher stress sensitivity (stress exponent, n = 9–13) at higher stresses irrespective of mineral ratio. Strain is localized along “slip zones” in a C and C′ orientation. The material in the slip zones shows extreme grain size reduction and flow features. At peak strength, 1–2 vol% of the sample is composed of slip zones that are straight and short. With increasing strain, the slip zones become anastomosing and branching and occupy up to 9 vol%; this development is concomitant with strain-weakening of the sample. Slip zones delimit larger cataclastic lenses, which develop a weak foliation. Our results suggest that strain localization leads to microstructural transformation of the rocks from a crystalline solid to a fluid-like material in the slip zones. The measured rheological response is a combination of viscous flow in the slip zones and cataclastic flow in coarser-grained lenses and can be modeled as a frictional slider coupled in parallel with a viscous dashpot.
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
Terms of Use
Creative Commons Attribution-Noncommercial-Share Alike
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1029/2020jb021262
