Precambrian Turbidites of Eqe Bay, Baffin Island: Stratigraphic, Structural and Geochronological Constraints on the Evolution of Canada's Arctic Greenstone Belts
Bibliographic record
Abstract
The Archean greenstone belts of the Mary River Group (2865-2706 Ma), or MRG, occur in northern Baffin Island and remain poorly understood in terms of structure, stratigraphy and metallogeny. The Eqe Bay greenstone belt is the least deformed and metamorphosed exposure of the MRG, and is divisible into a stratigraphically lower metavolcanic sequence and an overlying metasedimentary sequence. The upper sequence of the Eqe Bay belt consists mainly of a large turbiditic formation that unconformably overlies the lower volcanic and volcaniclastic sequence. Two primary units make up the metasedimentary sequence: (U1) a jointed polygenic conglomerate with a variable thickness between 100 and 250 m, that stratigraphically overlies the lower volcanic domain along the main unconformity; and (U2) an turbiditic formation with a maximum thickness of 6.5 km consisting mainly of wackes and graywackes including siltstone, argillites and meter-scale beds of granular polygenic conglomerate interbedded with sandstone. Two subunits are recognized within the turbidite succession: (U2.1) a distinctive 5 to 10m thick quartzite layer located near the base of the U2 turbidite sequence layer located near the base of the U2 turbidite sequence; and (U2.2) a thin iron formation interbedded with phyllite and garnet-rich schist. The unconformity at the base of the metasedimentary sequence is coincident with a major NE-SW trending, mylonitic shear zone that extends along the length of the Eqe Bay belt. We distinguish three deformation events affecting the metasedimentary belt: the first deformation is represented by a penetrative bedding-parallel foliation (S1) that is assumed to have developed during isoclinal folding. The second (S2) records is a penetrative fabric oblique to S1 associated with local F2 folds. The third event is recorded in localized strongly deformed zones that are characterized by a shallowly dipping crenulation cleavage (S3). U-Pb geochronological work on magmatic and detrital zircons provides an update on the stratigraphy and formation age of the greenstone belt as well as for the entire MRG. Meta-rhyolite from the volcanic sequence were dated at 2865 Ma, now the oldest age reported for the MRG. The youngest fraction of detrital zircons from a sample of the quartzite subunit (U2.2) located near the stratigraphic base of the turbidite unit yield an age of 2213 Ma. CL- 53 imagery and U/Th ratios are inconsistent with a metamorphic origin for these grains; instead they indicating post-Archean deposition. The metasedimentary sequence was likely deposited during the Paleoproterozoic and represents part of the Piling group, thereby expanding the regional footprint of this proto-Trans-Hudson basin sedimentary succession. Our results suggest that significant revision of the stratigraphy of the MRG and coeval greenstone belts of the Rae Craton may be required.
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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 | 0.002 | 0.001 |
| Scholarly communication | 0.002 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".