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https://doi.org/10.5194/se-2020-170
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2020-170
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  08 Oct 2020

08 Oct 2020

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This preprint is currently under review for the journal SE.

Frictional properties and microstructural evolution of dry and wet calcite-dolomite gouges

Matteo Demurtas1, Steven A.F. Smith2, Elena Spagnuolo3, and Giulio Di Toro3,4 Matteo Demurtas et al.
  • 1Physics of Geological Processes, The Njord Centre, Department of Geosciences, University of Oslo, Oslo, Norway
  • 2Department of Geology, University of Otago, Dunedin 9054, New Zealand
  • 3Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome 00143, Italy
  • 4Dipartimento di Geoscienze, Università degli Studi di Padova, 35131 Padova, Italy

Abstract. Calcite and dolomite are the two most common minerals in carbonate-bearing faults and shear zones. Motivated by field examples from exhumed seismogenic faults in the Italian Central Apennines, we investigated the frictional and microstructural evolution of gouge mixtures consisting of 50 wt % calcite and 50 wt % dolomite using a rotary-shear apparatus. The gouges were sheared at a range of slip rates (30 µm s−1–1 m s−1), displacements (0.05–0.4 m), and normal loads (17.5–26 MPa), under both room humidity and water-dampened conditions. The frictional behaviour and microstructural evolution of the gouges were strongly influenced by the presence of water. At room humidity, slip strengthening behaviour was observed up to slip rates of 0.01 m s−1, which was associated with gouge dilation and the development of a 500–900 µm wide slip zone cut by Y-, R-, and R1-shear bands. Above a slip rate of 0.1 m s−1, dynamic weakening accompanied the development of a localised <100 µm thick principal slip zone preserving microstructural evidence for calcite recrystallization and dolomite decarbonation, while the bulk gouges developed a well-defined foliation consisting of organized domains of heavily fractured calcite and dolomite. In water-dampened conditions, evidence of gouge fluidization within a fine-grained principal slip zone was observed at a wide range of slip-rates from 30 µm s−1 to 0.1 m s−1, suggesting that caution is needed when relating fluidization textures to seismic slip in natural fault zones. Dynamic weakening in water-dampened conditions was observed at 1 m s−1, where the principal slip zone was characterised by patches of recrystallized calcite. However, local fragmentation and reworking of recrystallized calcite suggests a cyclic process involving formation and destruction of a heterogeneous slip zone. Our microstructural data show that development of a well-defined gouge foliation at these experimental conditions is limited to high-velocity (>0.1 m s−1) and room humidity, supporting the notion that some foliated gouges and cataclasites may form during seismic slip in natural carbonate-bearing faults.

Matteo Demurtas et al.

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Matteo Demurtas et al.

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