| dc.description.abstract | Normally conditions in the forearc mantle wedge would cause stick-slip behaviour. However, the
forearc mantlewedge shows aseismic behaviour. Sections of the San Andreas fault also showaseismic
behaviour. Previous work suggested that serpentine was the cause of this aseismic behaviour,
in both forearc mantle wedges and the San Andreas fault. However, serpentine normally experiences
temperature strengthening and causes stick-slip in laboratory experiments, which means that
other weakening mechanisms are causing the aseismic behaviour.D E Moore et al., 2013 showed
that when serpentine is sheared against quartz it experiences decreasing friction with increasing
temperature. One explanation for this decrease could be the formation of talc due to its low friction
in comparison to serpentine. A reaction of serpentine with silica rich sources will form talc
which is stable over a wide range of temperature–pressure conditions and has a very low friction
coefficient. A second explanation is the activation of pressure solution which is activated by the
presence of quartz. Up till now, research on this topic has only been done up to temperatures of
350°C and few experiments have been conducted with quartz incorporated in the antigorite gouge.
In this research I show the effect of different weight percentages of quartz on the friction of antigorite
at temperatures up to 500°C. Experiments were conducted with the rotary shear aparatus at
different velocities. The experiments may give an insight in the frictional strength, expressed using
the rate and state parameters (a-b). Microstructural data of the experiments can give an insight in
the active deformation mechanisms in antigorite mixed with quartz during shearing. Experiments
conducted with antigorite containing quartz, show a significant decrease in friction and positive
(a-b) values which suggests that shearing is aseismic. Results from the microprobe, EDX and FTIR
prove the formation of talc during the experiments at temperatures of 500°C and the presence of
pressure-solution by pressure shadows and the dependence on grain size. In nature, these two
processes could be the cause of the aseismic behaviour within forearc mantle wedges and the San
Andreas fault. | |
