The Black Bay Shear Zone, northwestern Saskatchewan, lies within the Rae Province of the Canadian Shield. It is one of several major, northeast trending, steeply dipping shear zones that were active during the Paleoproterozoic Trans-Hudson or Thelon Orogenies. For part of its exposed length of approximately 50 km it separates Archean supracrustal gneisses of the Tazin Group to the northwest, from the unconformably overlying Paleoproterozoic, red-bed sequence of the Martin Group to the southeast. Deformation fabrics along the Black Bay Shear Zone indicate the sequential development of early ductile to late brittle episodes of movement. The early ductile episode (D<sub><font size=1>1</font></sub>, pre-Martin Gp) is characterized by a 1 km-wide mylonite belt in the Tazin gneisses, with mylonitic lamination (C-fabric), dextral ä-asymmetric winged porphyroclasts, stretch lineation (L<ub><font size=1>1</font></sub>) and rare sheath folds.
This was followed by a ductile to brittle transition (D<sub><font size=1>2</font></sub>, also pre-Martin Gp) characterized by small asymmetric folds in C, and small post-C compressional and extensional shear bands (SB) ranging from thin ductile shear zones to brittle fractures commonly vein filled. The late brittle phase (D<sub><font size=1>3</font></sub>, post-Martin Gp), to which uranium vein mineralization is related, included the formation of a major brittle fault zone along the southeastern side of the mylonitic shear zone, and several sets of vein filled joints. Movement directions during D<sub><font size=1>1</font></sub> to D<sub><font size=1>3</font></sub> are reflected by various shear sense indicators. The D<sub><font size=1>1</font></sub> dextral ä-asymmetrical winged porphyroclasts, combined with the gently NE and SW plunging L<sub><font size=1>1</font></sub>, stretch lineation, indicate sub-horizontal dextral displacement during the ductile phase of deformation. Predominantly NE-verging and steeply dipping SW plunging minor D<sub><font size=1>2</font></sub> folds, along with the predominantly dextral-verging, post-C shear bands, indicate that oblique dextral SE-side-up slip occurred during the ductile to brittle transition. Brittle movement (D<sub><font size=1>3</font></sub>)resulted in the preservation of an approximately 8-km thick succession of Martin Group on the SE-side of the fault, indicating a SE-side-down vertical throw of at least 8 km. The local presence of poorly preserved, down-dip slickenlineations suggests that at least some of this movement was dip slip. Time constraints on deformation are poor, tentatively all of the Black Bay Structure deformational history took place between 2300 Ma and 1700 Ma.
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-07242009-133017 |
| Date | 28 July 2009 |
| Creators | Bergeron, Julie |
| Contributors | Stauffer, Mel |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-07242009-133017/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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