Fault Geometry, Fluid Flow and Earthquake Rupturing

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Granite-greenstone belts in the Canadian shield are tran- sected by Archean shear zones and by younger more brittle strike- slip fault systems. Over wide areas, the Archean shear zones are now exposed at a structural level representing the base of the seismogenic zone (brittle-ductile transition) when the shear zones were active. Vein systems are concentrate where fluid pressures apparently intermittently attained supralithostatic values. These localized vein systems may represent fossil rupture nucleation sites for large earthquakes initiated by rapid upwards release of pressure. This project will map structural features in surface and subsurface exposures in two locations - yellow-knife NWT and Val d'Or mining district of Quebec. Laboratory work will include petrography and fluid inclusion analysis of the hydrothermal veins and associated wall rock. Results, while aimed primarily towards fundamental fault mechanics should also be applicable to improved understanding of mineralization processes in deep fault zones.