Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8914349 | Journal of Structural Geology | 2018 | 21 Pages |
Abstract
Shear experiments on quartz gouge were performed at elevated confining pressures (predominantly 1.5â¯GPa) and temperatures (500â¯Â°C - 1000â¯Â°C) at shear strain rates of 3.5·10â6 sâ1 to 2·10â3 sâ1 to study the brittle-to-viscous transition. An unsystematic temperature dependence of strength at low temperatures changes towards a clear temperature weakening dependence above 650â¯Â°C. The transition from a pressure strengthening to a pressure weakening relationship takes place continuously between 650â¯Â°C and 800â¯Â°C. Strain rate stepping experiments reveal power-law breakdown at low temperatures (â¼650â¯Â°C). Between 800â¯Â°C and 1000â¯Â°C, a stress exponent of nâ¯=â¯1.9â¯Â±â¯0.6 and an activation energy of Qâ¯=â¯170â¯Â±â¯72â¯kJ/mol indicate a combination of diffusion and dislocation creep. The Goetze criterion is confirmed as the upper stress limit for viscous deformation mechanisms. Localised deformation in the form of semibrittle shear bands with Riedel geometry at low temperatures changes to homogeneous deformation with a pervasive foliation accompanied by a continuous texture evolution between 700â¯Â°C and 1000â¯Â°C. Fracturing dominates at low temperatures accompanied by increasing amounts of dissolution and precipitation in fine-grained zones with increasing temperature. Above 650â¯Â°C, dislocation and diffusion creep are the dominating deformation processes, with dislocation creep being favoured in larger grains while dissolution-precipitation is active in the fine-grained fraction.
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Authors
Bettina Richter, Holger Stünitz, Renée Heilbronner,