CZECK, Dyanna M. and HUDLESTON, Peter J., Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Drive SE, Minneapolis MN, 55455, firstname.lastname@example.org
The Superior Province is comprised of approximately east - west trending subprovinces that are defined by lithological contrasts, metamorphic grade, and structural boundaries (Card and Ciesielski, 1986). A popular tectonic model for this province is the successive accretion of island arcs and their associated sediments (Hoffman, 1989). This study focuses on the boundary between the metavolcanic Wabigoon and the metasedimentary Quetico subprovinces near Mine Centre, Ontario. The Quetico contains mostly amphibolite facies metasediments, and the Wabigoon contains greenschist facies metavolcanics. Distinctive rocks found along this boundary are the Seine River Metasedimentary Group including the polymictic Seine River conglomerates. From stratigraphic evidence, the Seine River conglomerates formed late following the deposition of the volcanic sequences (Poulsen et al., 1980). Preliminary attempts at absolute dating have confirmed this (Davis et al., 1989). Previous structural work along this boundary described a dominant subvertical foliation transecting large folds (Poulsen, 1986; Tabor and Hudleston, 1991). These features are interpreted to have formed during dextral transpression.
The term "transpression" was first introduced by Harland (1971) to describe motion that is obliquely convergent, or motion partitioned into both convergent and strike-slip. In Harlandıs original paper, he described the development of folds and strike-slip structures due to oblique convergence. A specialized case of transpression was introduced by Sanderson and Marchini (1984). This idealized definition of transpression has been used to describe homogeneous deformation consisting of orthogonal simple shear and pure shear components with constant volume and confined deformation boundaries, possibly corresponding to the strain in deep ductile shear zones that accommodate oblique convergence. The dominant foliation along the Wabigoon - Quetico boundary seems to be related to this more specific type of transpression based on the flattening fabrics and asymmetric features indicating simple shear in the subhorizontal plane. One of the questions addressed by this study is the relationship between the folds and the dominant foliation. Clearly, it has been demonstrated that folds can form in transpression Harland (1971). Are the folds at this boundary consistent with the rest of the transpression fabric, or are they an earlier structural feature?
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