Isotopic and petrologic constraints on intracontinental deformation and metamorphism, Churchill Province, Nunavut
Bibliographic record
Abstract
The Canadian Churchill Province was the locus of repeated, regional reworking in the Paleoproterozoic associated with five major orogenic events that ultimately resulted in the formation of Earth’s first supercontinent, Nuna. Tectonic models for the Archean and Paleoproterozoic evolution of the Churchill Province have been formulated at the broadest scale, and consequently, the timing, nature and regional extent of deformation and metamorphism associated with these collisional events are poorly constrained. In this thesis, the metamorphic and deformation histories of two relatively unexplored regions in Nunavut were characterized in order to contribute to the understanding of the processes that reworked the boundaries and interior of the Churchill Province during development of Nuna. Aeromagnetic data and geological mapping on Boothia Peninsula, Nunavut, revealed the presence of a ~165 km long, 5-10 km wide high-strain zone, named the Sanagak Lake shear zone (SLsz), that marks the transition from dominantly N-trending Thelon-related structures in the north to SW-trending Trans-Hudson-related structures in the south. Field, microstructural, petrologic and isotopic data indicated that the SLsz is a south-dipping, strike-slip (sinistral) shear zone that formed in the mid-crust (~ 0.52 GPa) at 1804 ± 6 Ma. The timing, geometry and kinematics of high-strain deformation is consistent with north-directed compression associated with far-field stresses derived from the Trans-Hudson orogeny, and marks the northern limit of Trans-Hudson related deformation. Geologic mapping, phase equilibria modelling, and multi-mineral geochronology coupled with previously collected petrological and isotopic data from the Baker Lake area outline four lithotectonic domains named the Woodburn Lake and Ketyet River groups, Quoich River domain, Kramanituar Complex and the Thirty Mile domain. Each of these domains experienced distinct pressure – temperature – time – deformation (P-T-t-d) histories and are separated by shear zones that facilitated differential burial-exhumation in the Paleoproterozoic. All domains were buried and reworked, to varying degrees, between ca. 1.93 and 1.90 Ga during the Snowbird Orogeny. The Kramanituar Complex was exhumed rapidly following ca. 1.9 Ga metamorphism, whereas the Quoich River and Thirty Mile domains exhumed between ca. 1.87 and 1.85 Ga during the accretionary phases of the Trans-Hudson Orogeny.
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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 | 0.002 | 0.002 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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".