A QUANTITATIVE ANALYSIS OF STRAIN IN THE SEINE RIVER METACONGLOMERATES, RAINY LAKE REGION, NORTHERN ONTARIO, CANADA

The Seine River metaconglomerates were deformed shortly after deposition during the 2.7 Ga granite-greenstone forming orogeny of the central Superior Province. These rocks contain clasts of various compositions including granitoids, felsic volcanics, mafic volcanics, porphyritic volcanics, quartzites, and banded iron formations. The major fabric-forming deformation throughout the region can best be described as transpression with variable extrusion directions. The heterogeneous nature of the metaconglomerates results in competence contrasts, or variations in the resistance to deformation. Each of the clast types within the Seine responds to deformation differently, which is manifested through heterogeneous strain at the outcrop scale. The lithological role in the creation of competence contrasts was analyzed by utilizing the information contained in the heterogeneous strain data. These data were then used to quantify the heterogeneity of strain throughout the region.

Strain analyses were conducted separately for each clast type and the matrix using established methods (i.e. Fry and Rf/f). Preliminary strain analysis results allow us to rank clast “strength,” or ability to resist deformation. The “strengths” of the major clast types from lowest to highest are: metavolcanics, granitoids, and quartzites. When data from two outcrops are compared, the strain for each clast type varied, indicating that there is also a significant strain gradient on the overall regional scale. Parts of the Seine have undergone significant flattening, while others have undergone lesser flattening or plane strain.