SEISMIC SUPPRESSION VS SEISMIC EXPRESSION: EVIDENCE FROM THE MINAS FAULT ZONE, NOVA SCOTIA, CANADA

Crustal-scale faults, whether megathrusts or transcurrent zones, exhibit a broad range of material heterogeneities at different scales. On a macroscopic scale, juxtaposed rock units and faulting allow for widely differing mechanical behaviours over short distances, while at the microscopic scale, the addition of a weak phase (eg: phyllosilicates, graphite) can greatly influence the frictional strength of a fault. Seismic slip is anticipated to have occurred within exhumed examples of such faults by comparison with currently active tectonic regimes. Likewise evidence of rupture would be expected; however, discrete slip can be masked by interseismic aseismic creep and ductile flow at shallow crustal levels. Within the Greville Bay region of the transpressive Minas Fault Zone, Nova Scotia, Canada, a distinctive shear band domain is hosted within a black, chlorite rich phyllite, bounded on one side by a discrete fault followed by a folded variant of the same unit, and on the other side by a brecciated rhyolite containing seams of foliated cataclasite. Seismic slip is not evident in this unit, yet brittle rupture is clearly visible in the adjacent rhyolite . These material heterogeneities and their contrasting deformation mechanisms are examined at varying scales using optical microscopy, SEM, TEM, and XRD, to extract the interplay of processes that allow for seismic suppression versus seismic expression in the rock record.