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High‐strain creep of feldspar rocks: Implications for cavitation and ductile failure in the lower crust
Author(s) -
Rybacki Erik,
Wirth Richard,
Dresen Georg
Publication year - 2008
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2007gl032478
Subject(s) - materials science , porosity , cavitation , feldspar , superplasticity , strain hardening exponent , quartz , mineralogy , nucleation , grain size , composite material , geology , microstructure , physics , mechanics , chemistry , organic chemistry
Cavitation damage and ductile fracturing is a common phenomenon observed in high‐temperature, ambient pressure deformation of superplastic metals and ceramics, but hardly described for geological materials. We performed high‐pressure, high‐temperature (400 MPa, 950°C–1200°C) torsion experiments on fine‐grained (size ≈4 μ m, aspect ratio ≈2.5) synthetic feldspar aggregates containing <3 vol% residual glass. Samples deformed at constant strain rates (≈2 × 10 −5 – 2 × 10 −4 s −1 ) to high strain (≈2.8–5.6) reveal strain hardening at the lower strain rates. Microstructures show pronounced cavitation and formation of porosity bands containing redistributed glass, presumably associated with grain boundary sliding and shape‐preferred orientation of high‐aspect ratio feldspar grains. Sudden failure by strain‐induced nucleation, growth and coalescence of the cavities occurred in one‐third of the samples before deformation was terminated. In natural mylonites cavitation damage may produce increased porosity enhancing fluid flow in high‐temperature shear zones.