Semi-brittle deformation of granitoid gouges in shear experiments at elevated pressures and temperatures

Matej Pec, Holger Stünitz, Renée Heilbronner

Research output: Contribution to journalArticle

30 Scopus citations

Abstract

The physical and chemical processes acting in the 'brittle-to-plastic' transition are of great interest for a better understanding of fault rheology. We performed a series of experiments on granitoid gouge material under high confining pressures (Pc = 500-1500 MPa), temperatures (T = 300 °C and 500 °C) and fast shear strain rates (∼1.8 × 10 -4 s -1) where the material deforms by semi-brittle flow. Samples deformed at 500 °C are systematically weaker than samples deformed at 300 °C over the whole examined confining pressure range indicating a non-frictional component of the deformation. All samples develop an S-C' fabrics and deformation localizes in slip zones containing 'amorphous' feldspar material with an intermediate composition (Na, Ca and K-rich). Further, we observe changes in composition of feldspars (enrichment in the albite component) in the highly fragmented - but crystalline - regions with increasing finite shear strain. Our results indicate that mass-transfer processes keep pace with frictional deformation even at high strain rates and together with viscous flow of the 'amorphous' material are responsible for the observed strength difference.

Original languageEnglish (US)
Pages (from-to)200-221
Number of pages22
JournalJournal of Structural Geology
Volume38
DOIs
StatePublished - May 1 2012

Keywords

  • Brittle-plastic transition
  • Fault rocks
  • Microstructures
  • Rock deformation
  • Semi-brittle flow

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