Evidence for deep crustal seismic rupture in a granulite-facies, intraplate, strike-slip shear zone, northern Saskatchewan, Canada
Bibliographic record
Abstract
Research Article| September 24, 2018 Evidence for deep crustal seismic rupture in a granulite-facies, intraplate, strike-slip shear zone, northern Saskatchewan, Canada Omero F. Orlandini; Omero F. Orlandini † 1Department of Geological Sciences, University of Colorado, UCB 399, Boulder, Colorado 80309-0399, USA †orlandin@colorado.edu Search for other works by this author on: GSW Google Scholar Kevin H. Mahan; Kevin H. Mahan 1Department of Geological Sciences, University of Colorado, UCB 399, Boulder, Colorado 80309-0399, USA Search for other works by this author on: GSW Google Scholar Michael J. Williams; Michael J. Williams 2Department of Geosciences, University of Massachusetts, 627 North Pleasant Street, 233 Morrill Science Center, Amherst, Massachusetts 01003-9297, USA Search for other works by this author on: GSW Google Scholar Sean P. Regan; Sean P. Regan 2Department of Geosciences, University of Massachusetts, 627 North Pleasant Street, 233 Morrill Science Center, Amherst, Massachusetts 01003-9297, USA Search for other works by this author on: GSW Google Scholar Karl J. Mueller Karl J. Mueller 1Department of Geological Sciences, University of Colorado, UCB 399, Boulder, Colorado 80309-0399, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Omero F. Orlandini † 1Department of Geological Sciences, University of Colorado, UCB 399, Boulder, Colorado 80309-0399, USA Kevin H. Mahan 1Department of Geological Sciences, University of Colorado, UCB 399, Boulder, Colorado 80309-0399, USA Michael J. Williams 2Department of Geosciences, University of Massachusetts, 627 North Pleasant Street, 233 Morrill Science Center, Amherst, Massachusetts 01003-9297, USA Sean P. Regan 2Department of Geosciences, University of Massachusetts, 627 North Pleasant Street, 233 Morrill Science Center, Amherst, Massachusetts 01003-9297, USA Karl J. Mueller 1Department of Geological Sciences, University of Colorado, UCB 399, Boulder, Colorado 80309-0399, USA †orlandin@colorado.edu Publisher: Geological Society of America Received: 05 Sep 2017 Revision Received: 11 May 2018 Accepted: 27 Jun 2018 First Online: 24 Sep 2018 Online Issn: 1943-2674 Print Issn: 0016-7606 © 2018 Geological Society of America GSA Bulletin (2019) 131 (3-4): 403–425. https://doi.org/10.1130/B31922.1 Article history Received: 05 Sep 2017 Revision Received: 11 May 2018 Accepted: 27 Jun 2018 First Online: 24 Sep 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Omero F. Orlandini, Kevin H. Mahan, Michael J. Williams, Sean P. Regan, Karl J. Mueller; Evidence for deep crustal seismic rupture in a granulite-facies, intraplate, strike-slip shear zone, northern Saskatchewan, Canada. GSA Bulletin 2018;; 131 (3-4): 403–425. doi: https://doi.org/10.1130/B31922.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Pseudotachylyte veins are solidified frictional melt generated by localized high-strain-rate deformation, and they are commonly considered to be reliable geological indicators of seismic slip. While originally thought to occur primarily in the upper crust, field studies suggest pseudotachylyte can also form far below the frictional-viscous transition. This implies a more complex interplay between brittle and crystal-plastic deformation in crustal-scale fault systems. We report a new example of deep pseudotachylyte from the Paleoproterozoic granulite-facies strike-slip Cora Lake shear zone in northern Saskatchewan, Canada. Multiple generations of pseudotachylyte have been variably overprinted by plastic deformation and growth of high-grade metamorphic mineral assemblages (including garnet, orthopyroxene, and/or clinopyroxene). Undeformed pseudotachylyte generation surfaces locally display sinistral offsets, and deformed pseudotachylyte shows unambiguous shear sense indicators compatible with left-lateral Cora Lake shear zone kinematics. The vein networks are commonly proximal to and inherit kinematically compatible semibrittle shear fractures. Thermobarometry and modeling of mineral stability fields for the overprinted pseudotachylyte suggest vein generation between 0.7 and 0.8 GPa and 700 °C and 800 °C (corresponding to depths from 24 to 28 km). Combined with the kinematic compatibility and the well-constrained regional exhumation history, this suggests that the Cora Lake pseudotachylyte formed contemporaneously with the waning stages of deformation in the shear zone and constitutes one of the deepest examples of fault-related pseudotachylyte yet reported in North America. Evidence exists for several possible formation mechanisms, including in situ generation via ductile shear heating–induced plastic instabilities, as well as from interaction with earthquakes nucleating in the overlying brittle fault system. All of these possible mechanisms ultimately suggest a more rheologically complex environment than might typically be expected for these lower-crustal pressure and temperature conditions. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.010 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".