STRUCTURAL CHARACTERISTICS AND DISTRIBUTION OF STRAIN ASSOCIATED WITH DEXTRAL TRANSPRESSION ALONG THE LARDER LAKE-CADILLAC DEFORMATION ZONE IN THE SOUTHERN ABITIBI SUBPROVINCE, CANADA

This study aimed to establish the structural characteristics and extent of strain associated with the Larder Lake-Cadillac deformation zone (LLCdz) in the southern Abitibi subprovince. The structural history along the regional scale east-trending LLCdz and its immediate splays is well-constrained, because orogenic gold deposits are spatially associated with these deformation zones. The purpose of this study was to characterize the distribution of strain away from the immediate deformation zones, in order to investigate potential structural controls on gold mineralization and to gain a better understanding of the regional deformation history.

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 (S_D) and an associated moderately to steeply NE-plunging mineral/elongation lineation (L_D). S_D/L_D 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, S_D 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 S_D displays mm- to cm-scale spacing and L_D is weakly developed. Both fabrics are parallel to those observed in the HSZs. Because L_D is best developed in the HSZs, and because no overprinting relationships exist between the dextral fabrics and L_D, we believe that L_D 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 L_D 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.