Pb Isotope Mapping of Paleoproterozoic Gneisses in the SW Grenville Province: Evidence for a Cryptic Continental Suture
Bibliographic record
Abstract
New whole-rock lead (Pb) isotope analyses are presented in this study for granitoid orthogneisses from the Southwest Grenville Province in Ontario and Western Quebec. These data are used to test the location of a cryptic Archean-Proterozoic suture proposed on the basis of neodymium (Nd) isotope mapping. Immediately south of the inferred suture boundary, Pb isotope results show a crustal component derived solely from a juvenile Paleoproterozoic mantle source. These data are distinctly different from the reworked Archean craton to the northwest and strongly support the boundary derived from Nd isotope data. Pb signatures in the Paleoproterozoic crust suggest a southerly increase in magmatic reworking due to intensive plutonism during the late Paleoproterozoic and early Mesoproterozoic periods. The accretion of a juvenile arc to the Archean margin during the Penokean event (ca. 1.85 Ga) would have triggered subduction-zone reversal and the development of a long-lived ensialic arc on the composite margin. This was expressed as a 1.75 Ga Killarnian magmatic event and subsequent early Mesoproterozoic magmatism. This tectonic model for the Southwest Grenville Province shows that its crustal evolution is consistent with the Paleoproterozoic Makkovik-Ketilidian Orogen of Labrador and Southern Greenland. Hence, the application of whole-rock Pb isotope data in conjunction with Nd model ages provides data useful for mapping the extent of crustal terranes of differing age, which is essential for modeling the tectonic evolution of complex ancient accretionary orogens.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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".