U-Pb zircon geochronology of Archean greenstone belts (Mary River Group) and surrounding Archean to Paleoproterozoic rocks, northern Baffin Island, Nunavut
Bibliographic record
Abstract
Prior to 1:100,000-scale geological mapping conducted in 2017-2018, northern Baffin Island remained a major knowledge gap in the understanding of the northern Rae craton and the tectonic assembly of northeastern Laurentia. Geochronological data in the region was sparse; only four published U-Pb dates existed in the mapping area (~67,000 km2). Resolving the geology and age of the Archean Mary River Group - host to the Mary River iron mine - and the surrounding felsic-to-intermediate gneiss has key implications for the regional tectonic history and mineral prospectivity. In this study, we present new U-Pb zircon ages for 16 samples, including: 3 metavolcanic rocks and a quartzite from the Mary River Group; 2 psammite samples from newly discovered strata near Pond Inlet; 8 felsic-to-intermediate metaplutonic rocks; and 2 mafic metaplutonic rocks. Gneissic granodiorite to quartz diorite that forms the basement to the Mary River Group is dated herein at ca. 2901-2892 Ma. Taking into account previously published data, the age of gneissic basement beneath the Mary River Group is considered to be ca. 2901-2775 Ma. New ages of felsic-intermediate metavolcanic rocks from the Mary River Group define two phases of volcanism at ca. 2830 Ma and ca. 2760-2718 Ma, whereas quartzite from the Mary River Group has a maximum depositional age of ca. 2705 Ma. Psammite from the Pond Inlet area has a similar maximum depositional age of ca. 2720 Ma. Monzogranite and granodiorite and, less commonly, tonalite define an extensive ca. 2731-2706 Ma felsic plutonic suite. Mafic metaplutonic rocks near Pond Inlet, including a layered maficultramafic intrusion, yielded ages of ca. <2720 and >2655 Ma. Late, post-kinematic syenogranite was emplaced at ca. 1792 Ma. U-Pb dates of metamorphic zircon indicate that portions of northern Baffin Island experienced metamorphism during ca. 2.6-2.5 Ga, ca. 1926-1878, and 1850-1820 Ma. The new U-Pb zircon data reinforces lithological and tectonic correlations between northern Baffin Island and the Rae craton in Arctic Canada and West Greenland. Metamorphic U-Pb zircon data also suggest that northern Baffin Island may record tectonothermal activity associated with the Arrowsmith, Ellesmere-Inglefield, and/or Trans-Hudson orogens.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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 teacher head, 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".