The frictional strength of talc gouge in high‐velocity shear experiments

Abstract

Talc is present in several large‐scale fault zones worldwide and is mineralogically stable at temperature of the upper crust. It is therefore necessary to gain a better understanding of the frictional behavior of talc under a wide range of slip velocity conditions occurring during the seismic cycle. We analyzed the frictional and structural characteristics of room‐dry and water‐saturated talc gouge by shear experiments on a confined gouge layer at slip velocity range of 0.002–0.66 m/s and normal stress up to 4.1 MPa. Room‐dry talc showed a distinct slip‐strengthening with the initial friction coefficient of μ ~ 0.4 increased systematically to μ ~ 1 at slip distance D > 1 m. Room‐dry talc also displayed velocity‐strengthening at slip distances shorter than 1 m. The water‐saturated talc gouge displayed systematic low frictional strength of μ = 0.1–0.3 for the entire experimental range, with clear velocity‐strengthening behavior with positive (a‐b) values (rate dependence parameter of rate and state friction) of 0.01–0.04. The microstructural analyses revealed distributed shear and systematic dilation (up to 50%) for the room‐dry talc, in contrast to the extreme slip localization and strong shear compaction for water‐saturated talc. We propose that talc frictional strength is controlled by lubrication along cleavage surfaces that is facilitated by adsorbed water (room‐dry) and surplus water (water‐saturated). This mechanism can explain our experimental observations of slip‐strengthening and velocity‐strengthening for both types of talc gouge, as well as other clay minerals. It is thus expected that talc presence in fault zones would enhance creep and inhibit unstable slip.

Mantle exhumation at magma-poor rifted margins controlled by frictional shear zones

“…While we have not included this additional complexity, it may provide an explanation for reduced effective strain weakening in mantle materials. Alternatively higher fault healing as suggested by Püthe and Gerya 16 or different fault dynamics at a short time scale (velocity-strengthening of talc gouge 59 ) may explain reduced effective strain weakening in mantle materials.…”

Weak phases production and heat generation control fault friction during seismic slip

“…For serpentine rocks and clay-rich (smectite) gouges, the increase of temperature with velocity induces a dehydration of the material that can be evidenced by the presence of talc or illite. Yet, dry illite has a higher shear strength than dry smectite 26 and pure dry talc is a weak phase at low velocities but not for high velocities 27 . However, the phase transformation in these two cases involves also the release of water.…”

“…However, the phase transformation in these two cases involves also the release of water. The mixture of talc with water presents a friction coefficient of 0.2, almost independently of the velocity 27 . Also, the large amount of water produced by smectitedehydration induces the illite to present a large water content, which lowers the apparent friction coefficient 3 .…”

A new column collapse apparatus for the characterisation of the flowability of granular materials

“…Table 1 shows material properties of the selected materials. We report poured bulk density ρ p values corresponding Additionally, we present values of the friction coefficient µ s for the oats from published results in a review of properties of seeds and grains in [65]; values for fertiliser are estimated from measurements on copper oxide films exposed to air tested at short reaction times after their formation in [66]; and values for dry talc samples are also taken from experiments with slip distances of the order 10 −2 to 1 m [67], at the same scale of our run-out observations. Furthermore, we extract the particle sizes of these powders and bulk solids from the sieve analyses presented in Fig.…”