Episodic tremor and slow slip (ETS) downdip of the subduction seismogenic zone are poorly understood slip behaviors of the seismic cycle. Talc, a common metasomatic mineral at the subduction interface, is suggested to host slow slip but this hypothesis has not been tested in the rock record. We investigate actinolite microstructures from talc‐bearing and talc‐free rocks exhumed from the depths of modern ETS (Pimu'nga/Santa Catalina Island, California). Actinolite deformed by dissolution‐reprecipitation creep in the talc‐free rock and dislocation creep ± cataclasis in the talc‐bearing rock. This contrast results from stress amplification in the talc‐bearing rock produced by high strain rates in surrounding weak talc. We hypothesize that higher strain rates in the talc‐bearing sample represent episodic slow slip, while lower strain rates in the talc‐free sample represent intervening aseismic creep. This work highlights the need to consider fluid‐mediated chemical change in studies of subduction zone deformation and seismicity.
- Award ID(s):
- 1827951
- NSF-PAR ID:
- 10397742
- Date Published:
- Journal Name:
- NEW SOLUTIONS: A Journal of Environmental and Occupational Health Policy
- Volume:
- 31
- Issue:
- 2
- ISSN:
- 1048-2911
- Page Range / eLocation ID:
- 152 to 169
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The hydrous mineral talc is stable over a relatively large P‐T field and can form due to fluid migration and metamorphic reactions in mafic and ultramafic rocks and in faults along plate boundary interfaces. Talc is known to be one of the weakest minerals, making it potentially important for the deformation dynamics and seismic characteristics of faults. However, little is known about talc's mechanical properties at high temperatures under confining pressures greater than 0.5 GPa. We present results of deformation experiments on natural talc cylinders exploring talc rheology under 0.5–1.5 GPa and 400–700°C, P‐T conditions simulating conditions at deep faults and subducted slab interface. At these pressures, the strength of talc is highly temperature‐dependent where the thermal weakening is associated with an increased tendency for localization. The strength of talc and friction coefficient inferred from Mohr circle analysis is between 0.13 at 400°C to ∼0.01 at 700°C. Strength comparison with other phyllosilicates highlights talc as the weakest mineral, a factor of ∼3–4 weaker than antigorite and a factor of ∼2 weaker than chlorite. The observed friction coefficients for talc are consistent with those inferred for subducted slabs and the San Andreas fault. We conclude that the presence of talc may explain the low strength of faults and of subducted slab interface at depths where transient slow slip events occur.
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Abstract Talc is commonly found in the cores of exhumed faults and may be important to the dynamics of slip in active fault zones. To understand the rheology of talc at conditions relevant to subduction zones, we conducted torsional deformation experiments at high pressure (1 GPa) and temperatures (450–500°C). Scanning Transmission Electron Microscope imaging revealed a marked decrease in grain size with increasing strain, in addition to the development of grain kinking and nanoporosity. The similarity of these microstructures to talc deformed in natural faults and low‐pressure experiments indicates that the dominant deformation mechanisms of talc are similar across a wide range of depths. We conclude that frictional processes remain an important control on talc rheology even under high normal stresses. However, deformation‐induced porosity could enhance the percolation of high‐pressure or reactive fluids through talc‐rich lithologies.
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T g). POLYM. COMPOS., 40:2946–2953, 2019. © 2018 Society of Plastics Engineers -
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Abstract Talc formation via silica‐metasomatism of ultramafic rocks is believed to play key roles in subduction zone processes. Yet, the conditions of talc formation remain poorly constrained. We used thermodynamic reaction‐path models to assess the formation of talc at the slab‐mantle interface and show that it is restricted to a limited set of pressure–temperature conditions, protolith, and fluid compositions. In contrast, our models predict that chlorite formation is ubiquitous at conditions relevant to the slab‐mantle interface of subduction zones. The scarcity of talc and abundance of chlorite is evident in the rock record of exhumed subduction zone terranes. Talc formation during Si‐metasomatism may thus play a more limited role in volatile cycling, strain localization, and in controlling the decoupling‐coupling transition of the plate interface. Conversely, the observed and predicted ubiquity of chlorite corroborates its prominent role in slab‐mantle interface processes that previous studies attributed to talc.
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1177/1048291121996645
