STRUCTURAL CHARACTERISTICS AND DISTRIBUTION OF STRAIN ASSOCIATED WITH DEXTRAL TRANSPRESSION ALONG THE LARDER LAKE-CADILLAC DEFORMATION ZONE IN THE SOUTHERN ABITIBI SUBPROVINCE, CANADA
We present new structural data from a ~7x15 km area around the LLCdz in Kirkland Lake, Ontario. The dominant structural fabric is a steeply NNW- or SSE-dipping penetrative foliation (SD) and an associated moderately to steeply NE-plunging mineral/elongation lineation (LD). SD/LD is best developed in ENE-trending high-strain zones (HSZs) that are <1m to >100m in width, spaced at ~500 m, and occur up to 15 km from the LLCdz. Within the HSZs, SD is associated with dextral shear sense indicators such as Z-folds and sigma clasts and is commonly defined by sericite- and/or iron-carbonate mineral-rich folia. In the low strain domains SD displays mm- to cm-scale spacing and LD is weakly developed. Both fabrics are parallel to those observed in the HSZs. Because LD is best developed in the HSZs, and because no overprinting relationships exist between the dextral fabrics and LD, we believe that LD developed during dextral shear and is indicative of a subvertical extension component. This is consistent with earlier interpretations of dextral transpression along the LLCdz. The fact that LD in the HSZs is parallel to those in the low strain domains implies that the subvertical extension component was substantial in these zones, either because the kinematic vorticity number was low and/or because strain was high. The association between alteration and deformation in the transpressional HSZs suggests that they may be prospective relatively distal to the LLCdz in the Kirkland Lake area. The evidence for substantial subvertical extension may imply that significant crustal thickening occurred during dextral transpression.