TY - JOUR
T1 - Coseismic recrystallization during shallow earthquake slip
AU - Smith, S. A.F.
AU - Di Toro, G.
AU - Kim, S.
AU - Ree, J. H.
AU - Nielsen, S.
AU - Billi, A.
AU - Spiess, R.
N1 - Copyright:
Copyright 2013 Elsevier B.V., All rights reserved.
PY - 2013/1
Y1 - 2013/1
N2 - Solidifi ed frictional melts, or pseudotachylytes, remain the only unambiguous indicator of seismic slip in the geological record. However, pseudotachylytes form at >5 km depth, and there are many rock types in which they do not form at all. We performed low- to high-velocity rock friction experiments designed to impose realistic coseismic slip pulses on calcite fault gouges, and report that localized dynamic recrystallization may be an easy-to-recognize microstructural indicator of seismic slip in shallow, otherwise brittle fault zones. Calcite gouges with starting grain size <250 μm were confi ned up to 26 MPa normal stress using a purpose-built sample holder. Slip velocities were between 0.01 and 3.4 m s-1, and total displacements between 1 and 4 m. At coseismic slip velocities ≥0.1 m s-1, the gouges were cut by refl ective principal slip surfaces lined by polygonal grains <1 μm in size. The principal slip surfaces were fl anked by <300 μm thick layers of dynamically recrystallized calcite (grain size 1-10 μm) containing well-defi ned shape- and crystallographic-preferred orientations. Dynamic recrystallization was accompanied by fault weakening and thermal decomposition of calcite to CO2 + CaO. The recrystallized calcite aggregates resemble those found along the principal slip surface of the Garam thrust, South Korea, exhumed from <5 km depth. We suggest that intense frictional heating along the experimental and natural principal slip surfaces resulted in localized dynamic recrystallization, a microstructure that may be diagnostic of seismic slip in the shallow crust.
AB - Solidifi ed frictional melts, or pseudotachylytes, remain the only unambiguous indicator of seismic slip in the geological record. However, pseudotachylytes form at >5 km depth, and there are many rock types in which they do not form at all. We performed low- to high-velocity rock friction experiments designed to impose realistic coseismic slip pulses on calcite fault gouges, and report that localized dynamic recrystallization may be an easy-to-recognize microstructural indicator of seismic slip in shallow, otherwise brittle fault zones. Calcite gouges with starting grain size <250 μm were confi ned up to 26 MPa normal stress using a purpose-built sample holder. Slip velocities were between 0.01 and 3.4 m s-1, and total displacements between 1 and 4 m. At coseismic slip velocities ≥0.1 m s-1, the gouges were cut by refl ective principal slip surfaces lined by polygonal grains <1 μm in size. The principal slip surfaces were fl anked by <300 μm thick layers of dynamically recrystallized calcite (grain size 1-10 μm) containing well-defi ned shape- and crystallographic-preferred orientations. Dynamic recrystallization was accompanied by fault weakening and thermal decomposition of calcite to CO2 + CaO. The recrystallized calcite aggregates resemble those found along the principal slip surface of the Garam thrust, South Korea, exhumed from <5 km depth. We suggest that intense frictional heating along the experimental and natural principal slip surfaces resulted in localized dynamic recrystallization, a microstructure that may be diagnostic of seismic slip in the shallow crust.
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U2 - 10.1130/G33588.1
DO - 10.1130/G33588.1
M3 - Article
AN - SCOPUS:84872165734
VL - 41
SP - 63
EP - 66
JO - Geology
JF - Geology
SN - 0091-7613
IS - 1
ER -