Timing and kinematics of post-Timiskaming deformation within the Larder Lake-Cadillac deformation zone, southwest Abitibi greenstone belt, Ontario, Canada~1

摘要

The Larder Lake-Cadillac deformation zone is oneof several anastomosing zones of high strain within the Abitibigreenstone belt. In the Kirkland Lake area, Ontario, the LarderLake-Cadillac deformation zone is characterized by extensivecarbonate and chlorite alteration, strong south-dipping foliations,and steep lineations. These features formed during two ductiledeformation increments, D_2 and D_3, that occurred afterdeposition of Timiskaming assemblage sediments. D_2 strainaccumulation and greenschist facies metamorphism and alterationwere localized within the deformation zone, facilitated bychannelling of hydrothermal fluids within a preexisting structure,possibly formed during early D_1 terrane accretion. During D_2north-south shortening, east-west-trending sectors of thedeformation zone accumulated bulk coaxial strains, whilesoutheast-and northeast-trending sectors experienced, respectively,dextral and sinistral transpressive deformations. Preservation ofTimiskaming assemblage sediments in the footwall of thedeformation zone indicates a component of south-over-north(reverse) displacement that is not recorded by D_2 fabrics.Northwest-southeast D_3 compression resulted in the formationof a regional, northeast-striking cleavage formed under regionalgreenschist facies conditions, and local dextral reactivation ofsuitably oriented sections of the Larder Lake-Cadillac deformationzone. The Murdoch Creek and Lebel stocks abut the Larder Lake-Cadillac deformation zone. Their internal structure andemplacement are interpreted to be a consequence of D_2 north-south shortening. Magmetic zircon and titanite in the MurdochCreek and Lebel stocks yield U-Pb geochronology ages of 2672+－2 and 2673+－2 Ma, providing a maximum age forD_2deformation. Hydrothermal titantite associated with S_3foliation in the Murdoch Creek stock gives an U－Pb age of2665+－4 Ma, the maximum age of D_3 deformation. Plutonemplacement, deformation, and coincident metamorphismoccurred over a span of 1 Ma (from 2670 to 2669 Ma) to over 14Ma (from 2675 to 2661 Ma), during a regime of north-south,followed by northwest-southeast, regional shortening.