Thermomechanics of an extensional shear zone, Raft River metamorphic core complex, NW Utah

Raphaël Gottardi, Christian Teyssier

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27 Scopus citations


A detailed structural and microstructural analysis of the Miocene Raft River detachment shear zone (NW Utah) provides insight into the thermomechanical evolution of the continental crust during extension associated with the exhumation of metamorphic core complexes. Combined microstructural, electron backscattered diffraction, strain, and vorticity analysis of the very well exposed quartzite mylonite show an increase in intensity of the rock fabrics from west to east, along the transport direction, compatible with observed finite strain markers and a model of "necking" of the shear zone. Microstructural evidence (quartz microstructures and deformation lamellae) suggests that the detachment shear zone evolved at its peak strength, close to the dislocation creep/exponential creep transition, where meteoric fluids played an important role on strain hardening, embrittlement, and eventually seismic failure. Empirically calibrated paleopiezometers based on quartz recrystallized grain size and deformation lamellae spacing show very similar results, indicate that the shear zone developed under stress ranging from 40MPa to 60MPa. Using a quartzite dislocation creep flow law we further estimate that the detachment shear zone quartzite mylonite developed at a strain rates between 10-12 and 10-14s-1. We suggest that a compressed geothermal gradient across this detachment, which was produced by a combination of ductile shearing, heat advection, and cooling by meteoric fluids, may have triggered mechanical instabilities and strongly influenced the rheology of the detachment shear zone.

Original languageEnglish (US)
Pages (from-to)54-69
Number of pages16
JournalJournal of Structural Geology
StatePublished - Aug 2013

Bibliographical note

Funding Information:
We gratefully acknowledge research support from the Swiss Science Foundation ( FNS-117694 ) and the US-National Science Foundation ( EAR-0838541 ). Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program. Finally, we thank JSG editor Joao Hippertt and reviewers R. Weinberg and W. Sullivan for their detailed reviews and constructive advice.


  • Deformation lamellae
  • Extensional detachment
  • Metamorphic core complex
  • Paleopiezometry
  • Quartz deformation
  • Rheology
  • Thermomechanics


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