Project Abstract
|
We investigate the deformation mechanisms and slip processes at high temperature conditions, either in the presence of water [hydrothermal conditions] or at frictional heat melt conditions. At the intersection of the NNW-trending Elsinore fault and the inactive West Salton detachment fault we show that damage along the Elsinore ranges in thickness from a narrow slip plane to > 100 m along the eastern flank of the Tierra Blanca Mountains. Thermal fluids (~30°C) emerge at the intersection of the West Salton detachment and Elsinore faults actively alter the host rock, already fractured and crushed during fault slip. Fault cores contain thin chlorite ± epidote zones. The NW-striking West Salton detachment fault (WSDF) is a low-angle normal fault that formed and slipped at a low-angle (<30°). We document the presence of 0.1 cm to 2 m-thick, aphanitic, fault-related rocks. Microstructural and electron beam methods established a melt origin for these fault-rocks. In the cored rocks from the Cajon Pass, deformation and alteration of fault-related rocks adjacent to the steeply dipping Cleghorn fault span the brittle to semi-brittle deformational regime at hydrothermal conditions. Fault frequency increases with depth, and fracture densities are greater around fault zones. This fault correlates well with the left-lateral steeply dipping Cleghorn fault, and reflects the interaction between hydrothermal and deformation processes at depth. The data also show that damage zones are a long-lived presence of the deformed and altered zones of reduced elastic moduli associated with faults, and that semi-brittle distributed shearing may occur at depths as shallow as 3-4 km. |
