Early weakening processes inside thrust fault

摘要: Observations from deep boreholes at several locations worldwide, laboratory measurements of frictional strength on quartzo-feldspathic materials, and earthquake focal mechanisms indicate that crustal faults are strong (apparent friction μ ≥ 0.6). However, experiments phyllosilicate-rich rocks some geophysical data have demonstrated major considerably weaker. This weakness is commonly considered to be characteristic mature in which altered by prolonged deformation fluid-rock interaction (i.e., San Andreas, Zuccale, Nankai Faults). In contrast, this study we document fault weakening occurring along a marly shear zone its infancy (<30 m displacement). Geochemical mass balance calculation microstructural show massive calcite departure (up 50 vol %) the facilitated concentration reorganization weak phyllosilicate minerals surfaces. Friction carried out intact foliated samples host marls structural lead significant incipient structure has slip behavior comparable previously documented. These results faults, especially those nucleating lithologies rich both clays high-solubility (such as calcite), might experience rapid mineralogical alteration become even early stages their activity.