Rutile Ages and Thermometry Along a Grenville Anorthosite Pathway
Bibliographic record
Abstract
Abstract The Grenville Orogen, in North America, contains a belt of Proterozoic anorthosite massifs with an episodic emplacement history. These distinctive magmas reflect extensive fractional crystallization of plagioclase from a mafic magma and contain layers dominated by Ti‐bearing minerals including ilmenite and rutile. U‐Pb geochronology and Zr‐in‐rutile analyses from the Lac Malbaie complex in the Saint Urbain area of Quebec help to constrain the tectonothermal history of repeated anorthosite emplacement into the crust. Geologically significant dates were obtained from low‐U (<2 ppm) rutile in anorthosite drill cores and a boulder. Rutile ages of c. 1158, 1069–1056, and 936–910 Ma are interpreted to reflect variable modification of cooling ages during later intrusion and fluid mobilization events. Zr‐in‐rutile temperatures track higher apparent temperatures of >800°C in earlier events. Apparently younger rutile grains, and those influenced by fast pathway diffusion, record lower apparent temperatures. The Grenville Orogen comprises major trans‐lithospheric structures that facilitate the repeated bottom‐up transit of mantle‐derived magmas. At depth this led to the emplacement of anorthositic magmas whose thermal pathway is tracked by rutile passing through their Pb blocking temperature during crustal unroofing. This same broad crustal architecture, in the comparatively shallow crust, provided a favorable pathway for top‐down hydrothermal fluids to interact with younger rutile as successive anorthosites were emplaced. Rutile demonstrates that the current crustal section represents the juxtaposition of minerals preserving information from different thermal regimes, retaining vestiges of a protracted history due to incomplete re‐equilibration with subsequent chemical or thermal conditions.
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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 | 0.000 | 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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; both teacher heads agree on what is shown here.
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".