Structural analysis of the Paint Lake Deformation Zone, Northern Ontario /

The Paint Lake Deformation Zone (PLDZ), located within the Superior Province of Canada, demarcates a major structural and lithological break between the Onaman-Tashota Terrane to the north and the Beardmore-Geraldton Belt to the south. The PLDZ is an east-west trending lineament, approximately 50 km in length and up to 1 km in width, comprised of an early ductile component termed the Paint Lake Shear Zone and a late brittle component known as the Paint Lake Fault. Structures associated with PLDZ development including S-, C- and C'-fabrics, stretching lineations, slickensides, C-C' intersection lineations, Z-folds and kinkbands indicate that simple shear deformation dominated during a NW-SE compressional event. Movement along the PLDZ was in a dextral sense consisting of an early differential motion with southside- down and a later strike-slip motion. Although the locus of the PLDZ may in part be lithologically controlled, mylonitization which accompanied shear zone development is not dependent on the lithological type. Conglomerate, intermediate and mafic volcanic units exhibit similar mesoscopic and microscopic structures where transected by the PLDZ. Field mapping, supported by thin section analysis, defines five strain domains increasing in intensity of deformation from shear zone boundary to centre. A change in the dominant microstructural deformation mechanism from dislocation creep to diffusion creep is observed with increasing strain during mylonitization. C'-fabric development is temporally associated with this change. A decrease in the angular relationship between C- and C'-fabrics is observed upon attaining maximum strain intensity. Strain profiling of the PLDZ demonstrates the presence of an outer primary strain gradient which exhibits a simple profile and an inner secondary strain gradient which exhibits a more complex profile. Regionally metamorphosed lithologies of lower greenschist facies outside the PLDZ were subjected to retrograde metamorphism during deformation within the PLDZ.

Determining rotational direction of rotation structures using prolate shaped grains within till

Micromorphology is used to analyze a wide range of sediments. Many microstructures have, as yet, not been analyzed. Rotation structures are the least understood of microstructures: their origin and development forms the basis of this thesis. Direction of rotational movement helps understand formative deformational and depositional processes. Twenty-eight rotation structures were analyzed through two methods of data extraction: (a) angle of grain rotation measured from Nikon NIS software, and (b) visual analyses of grain orientation, neighbouring grainstacks, lineations, and obstructions. Data indicates antithetic rotation is promoted by lubrication, accounting for 79% of counter-clockwise rotation structures while 21 % had clockwise rotation. Rotation structures are formed due to velocity gradients in sediment. Subglacial sediments are sheared due to overlying ice mass stresses. The grains in the sediment are differentially deformed. Research suggests rotation structures are formed under ductile conditions under low shear, low water content, and grain numbers inducing grain-to-grain interaction.

HG 186.9-187.0 D.E-2

Coarse grained sediment with small patches of a fine grained domain. The domain may contain organic material. Lineations and minor grain stack present throughout the section.

HG 186.9-187.0 D.E-3

Fractured and weathered grains throughout the section. Lineations and grain stacks throughout the section.

HG 186.9-187.0 D.E-4

Fine grained domain within a coarse grained domain. Lineations throughout the section. A few small patches of a clay domain seen towards the top left.

HG 186.15-186.25-3

Major grain crushing towards the centre of the section. A few lineations and grain stacks also present.

HG 186.55-186.75-1

Domain boundaries observed between the fine grained and coarse grained sediment. The coarse grained sediment contains lineations.

HG 186.15-186.25 Thin Section

Coarse grained sample with multiple fine grained domains. Clasts range from small to medium and sub-angular to sub-rounded. Mainly contains grain crushing (with grains crushed into one another) and short distance lineations. A few rotation structures are seen and fine grained sand domains can also be seen.

HG 186.80-186.85 Thin section

A coarse grained sample with clay rich domains. Grains range from small to medium and are sub-angular. Rotation structures can be seen around sub-rounded clasts. Lineations can be seen throughout the image, mainly short distance lineations. Small comet structures can also be seen throughout the images.

HG 186.9-187.0 D.E.

Coarse grained sediment with a few fine grained matrices. Brown sediment with small to medium sized clasts. Clasts range from sub-angular to sub-rounded. Organic material present. It contains rotation structures throughout as well as edge-to-edge grain crushing. Fine grained clay domains are present and lineations can also be seen. Minor amounts of grain stacking can also be seen.

HG 186.9-187.0 D.E. Thin Section

Coarse grained sample with grains varying from small to medium in size. They range from sub-angular to sub-rounded in shape. The sample is abundant in lineations and comet structures. Minor amounts of grain stacking are present. Inclusions of a clay rich, fine grained domain.

HG 187.45-187.65 Thin Section

Coarse grained sediment with fine grained domains throughout. The clasts in the coarse grained domain range from sub-angular to sub-rounded. Short distance lineations are present throughout the sample. Organic rich domains (darker) are prevalent alongside fractured grains.

HG 188.30-188.35

Very fine grained. Organic matter present. Lineations can also be seen throughout, mainly in one orientation suggesting a masepic fabric.

HG 188.60-188.70 Thin Section

Dark brown sediment with mainly small grains. Clasts are sub-angular. Abundant in lineations, grain stacking, and minor grain crushing. Lineations are oriented in multiple directions.

HG 195.45-195.55 Thin Section

Dark brown sediment with clasts ranging from small to large. The grains are sub-angular. Two main domains can be seen. Both are coarse grained, but one contains larger grains and potentially more clay material. Lineations are present throughout the sample in multiple directions. Minor rotation around a few larger clasts can be seen, as well as comet structures.