Abstract: In situ Hf-isotope zircon data from two Paleoproterozoic bimodal volcanic segments of the Aillik Group, Makkovik Province, Labrador
Bibliographic record
Abstract
The Makkovik Province of eastern Labrador is part of an accretionary orogenic belt that formed during the Paleoproterozoic Makkovikian orogeny. The Aillik domain of the Makkovik Province is largely composed of: a) the Aillik Group, a package of Paleoproterozoic, polydeformed, bimodal volcano-sedimentary rocks, and b) abundant variably deformed Paleoproterozoic intrusive suites that intrude the Aillik Group. Two areas are the focus of this study. Middle Head is dominated by lower amphibolite facies arkosic sandstone, felsic tuff, rhyolite and basalt. Pomiadluk Point is composed primarily of lower amphibolite to upper greenschist facies felsic tuff and polymictic conglomerate with lesser preserved rhyolite and basalt. Recent detailed 1:10 000 scale bedrock mapping in conjunction with in situ Hf-isotopic geochemistry of zircon illustrate that the Aillik Group was deposited on ca 2.5 Ga crust at Middle Head, and mainly on ca 2.8 Ga crust at Pomiadluk Point. Hf-isotope data was collected by LA-MC-ICPMS. eHfi in zircon from a ca. 1850 Ma felsic tuff range uniformly from -2.0 to -4.9 with crust formation ages of ca 2.4 to 2.6 Ga for their felsic crustal sources. In contrast, two felsic tuff samples at Pomiadluk Point with magmatic ages of ca. 1855 and 1860 Ma have eHfi values in zircon that range from -4.8 to -12.0 in 19 of 23 grains analyzed, giving (felsic) crust formation ages of 2.6 to 3.0 Ga. A third sample from Pomiadluk Point, a ca. 1863 Ma foliated, laminated, fine-grained tuffaceous sandstone that outcrops between two conglomerate beds contains magmatic zircons with eHfi that range from +3.7 to -2.0, and crust formation ages of 2.2 to 2.5 Ga. The new Hf-isotope data suggest that the Aillik Group was deposited on crust that had an age range of at least 800 Ma and included both Paleoproterozic and Late Archean components. None of the felsic volcanic rocks analyzed from the Aillik Group show Hf-isotope evidence of derivation from truly juvenile, 1.9-2.0 Ga crust with short residence times (<100 Ma), as might be expected for an intra-oceanic island arc origin.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".