The effects of fault orientation and fluid infiltration on fault rock assemblages at seismogenic depths

摘要: Abstract The factors controlling the development of different types fault rock assemblages and, more specifically, formation friction melts are still not fully understood. In this study we compared two exhumed strike–slip faults in Adamello batholith (Southern Alps): Gole Larghe and Passo Cercen zones, active at 9–11 km depth temperatures 250–300 °C. Each zone consists hundreds sub-parallel strands exploiting pre-existing joints. strikes N105 ± 5° is dextral; rocks cataclasites widespread, centimetre-thick pseudotachylytes. on average N130° formed by multiple horizons: segments striking N105°–N130° mainly dextral, whereas N135°–N140° sinistral. Microstructural, mineralogical geochemical investigations show that associated with thick epidote + K-feldspar + quartz veins rare, millimetre-thick Field evidence suggests both direction maximum horizontal stress σ 1 was N135°. about 30° to favourably oriented for reactivation. By contrast, low angles unfavourably reactivation, therefore requiring high pore pressures, as suggested occurrence extensive epidote veining hydraulic breccias. It proposed frictional melting inhibited pressures effective normal stresses.