Date of Award

May 2014

Degree Type

Thesis

Degree Name

Master of Science

Department

Geosciences

First Advisor

Dyanna M. Czeck

Committee Members

Barry I. Cameron, Julie A. Bowles

Keywords

Archean, Structural Geology, Tectonics

Abstract

The Rice Bay and Northeast Bay gneiss domes (RBD and NEBD) are two tonalitic rock units located in the Archean Rainy Lake zone of the Superior Province. The Rainy Lake zone acts as a boundary between two subprovinces, accommodating transpression, significant shortening and dextral motion in its lithologic assemblage. This study contributes to understanding how deformation is partitioned in heterogeneous terranes, and also demonstrates a practical method of kinematic analysis. Foliations, lineations, shear zones, tension gashes, quartz veins, mafic enclaves, and folded and boudined veins were all utilized in the kinematic analysis. Foliation orientations in both domes are consistent with the overall foliation of the region, but the lineation orientations are less steeply plunging than most of the surrounding area. Shear zones in the RBD indicate shortening through sets of sinistral and dextral shears, while in the NEBD only dextral shear zones are observed. Strain analysis of mafic enclaves in the RBD indicate plane strain at lower magnitudes, while folded and boudined veins in the NEBD indicate slightly higher plane strain. Tension gashes related to late stage exhumation exhibit some sense of rotation, indicating that transpression was still occurring during the final stages of deformation. Models of triclinic transpression with oblique simple shear and extrusion directions were fit to the lineation and strain data observed in both units. The shear obliquity angle is similar for both units (approximately 20° E) and the angle of extrusion is subvertical for both. The kinematic vorticity estimates differ between the two units indicating that the bulk rock in the RBD was accommodating mostly dextral shear whereas the bulk rock in the NEBD was accommodating mostly shortening. The set of triclinic models previously determined for the rest of the Rainy Lake area are similar, but the amount of partitioning between pure shear and simple shear and the extrusion angle differ in other rock units.

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