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Rheology and the evolution of physical properties with increasing temperature and strain: in illite+quartz and muscovite+quartz systems

English title Rheology and the evolution of physical properties with increasing temperature and strain: in illite+quartz and muscovite+quartz systems
Applicant Burg Jean-Pierre
Number 116153
Funding scheme Project funding (Div. I-III)
Research institution Geologisches Institut ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geology
Start/End 01.10.2007 - 30.09.2010
Approved amount 566'390.00
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All Disciplines (2)


Keywords (13)

experimental rock deformation; experimental petrophysics; rheology of two-phase rocks; seismic properties; anisotropy; clay; Rheology; experimental deformation; metapelite; quartz; mica; physical properties; torsion

Lay Summary (English)

Lay summary
This proposal deals with the role of phyllosilicates namely clay and mica, and their interaction with quartz during rock deformation. Experiments conducted so far contradict the common assumption that clay-bearing fault gouges are weak zones that undergo strain weakening during deformation. Instead, clay displays strain hardening up to shear strains of gamma = 5. It has been argued that weakening may occur at larger strains or may result from the build up of pore pressure in extremely low permeability clay. It also has been proposed that most of deformation in natural clay-bearing faults is localized on very thin and flat surfaces parallel to the gouge boundary, the so-called Y-fractures. These have never been fully reproduced experimentally, because until the advent of torsion deformation, the strain achievable in laboratory was too small compared to nature. The same concern exists at higher metamorphic grade for mica-rich, strain-localizing zones.
We will experimentally study rock deformation/seismic property up to very large torsion/shear strain on two-phase synthetic aggregates ranging in composition from pure illite to pure quartz at increasing temperature until melting under controlled water pressure conditions. The strain level that we were able to achieve in our laboratory is one order of magnitude larger than that obtained previously with other techniques; this amount of deformation should permit reaching weakening in the phyllosilicate-rich aggregates and to reproduce Y-fractures. Measuring seismic properties will serve to monitor the anisotropy build up during deformation and to correlate strain with anisotropy. This information will provide new constraints on the interpretation of seismic signals that detect the natural anisotropy of rocks. We will span a wide metamorphic range, from sub-diagenetic to melting conditions, for constant bulk compositions of rocks. Clay minerals and micas undergo successive dehydration reactions with increasing temperature, a key process increasing pore pressure, hence reducing normal stress. In addition, we will analyse the reaction products at high temperature, where metastable phases (aluminosilicates and even melt) are produced at the onset of dehydration reactions of muscovite and quartz.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants


Associated projects

Number Title Start Funding scheme
132722 Rheology and evolution of physical properties with increasing temperature and strain in illite+quartz and muscovite+quartz systems 01.10.2010 Project funding (Div. I-III)