Uivak II augen gneiss from the Saglek Block, Labrador: the current state of play
Bibliographic record
Abstract
Interpreting Archean geology is often challenging due to the rocks having obscure field relationships and polymetamorphic histories (Kusiak et al. 2019; Dunkley et al. 2020). In such circumstances, U-Pb isotopic analysis of zircon is crucial for revealing the geological history. This study investigates Archean gneisses from the Saglek Block in Canada, which record magmatic and metamorphic history between ca 3.9 Ga and 2.5 Ga. The predominant lithology is the Uivak gneiss which is primarily composed of tonalite-trondhjemite-granodiorite (TTG) with subordinate intermediate to mafic components. Uivak gneiss is traditionally divided into Uivak I and Uivak II, where Uivak I is grey gneiss and Uivak II is characterized by augen texture and Fe-rich geochemistry (Collerson and Bridgwater, 1979). Ages for the magmatic protoliths of Uivak I are >3.6 Ga, whereas Uivak II ages vary between ca 3.6-3.3 Ga (Sałacińska et al. 2019; Wasilewski et al. 2021 and references therein). This study presents geochemical and U-Pb zircon geochronology from Mentzel and Maidmonts Islands. Augen gneiss on Mentzel Island fits the definition of Uivak II augen gneiss and yield a U-Pb zircon age of ca 3.3 Ga. A similar age was reported for Maidmonts gneiss (Sałacińska et al. 2019) and Illuilik gneiss (Wasilewski et al. 2021). On Mentzel Island, granitic bodies intruded the augen gneiss at ca 2.7 Ga and 2.5 Ga during high-T metamorphism. New dating confirms that augen gneiss on Mentzel Island and elsewhere in the Saglek Block belongs to Uivak II gneisses of ca 3.3 Ga. Variations in rare earth element concentration between different ca 3.3 Ga rocks can be attributed to the involvement of different crustal components in the magmatic protolith. On Maidmonts Island, the augen gneiss intrudes grey gneiss with a protolith age of ca 3.7 Ga, which confirms deformation and metamorphism of Uivak I gneiss before ca 3.3 Ga. This research was funded by NCN grants UMO2019/34/H/ST10/00619 to MAK. References:Collerson, K.D. & Bridgwater, D. 1979. Metamorphic development of early Archaean tonalitic and trondhjemitic gneisses: Saglek area, Labrador. In: Barker, F. (Ed.), Trondhjemites, Dacites, and Related Rock. Elsevier, Amsterdam, 205–271.Dunkley et al. 2020. Journal of the Geological Society, 177 (1), 31–49.Kusiak et al. 2018. Chemical Geology, 484, 210–223.Sałacińska et al. 2019. International Journal of Earth Sciences, 108, 753-778.Wasilewski et al. 2021. Precambrian Research, 359, 106092.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.003 |
| Science and technology studies | 0.002 | 0.002 |
| Scholarly communication | 0.003 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 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".