Sm‐Nd Geochemistry and U‐Pb Geochronology of the Mont Rigaud Stock, Quebec, Canada: A Late Magmatic Event Associated with the Formation of the Iapetus Rift
Bibliographic record
Abstract
The Mont Rigaud Intrusion is a syeno‐granitic stock located in the St. Lawrence River–Ottawa River Graben and surrounded by sedimentary rocks of the St. Lawrence Lowlands. The intrusion is circular and divided into three units: an outer ring of hornblende syenite, an inner ring of feldspar‐hornblende syenite, and an inner core of quartz syenite and granite. Geochemical, U‐Pb, and Nd isotopic data gathered from the stock indicate that all three units are comagmatic and were intruded within a short period of time. Rock samples from the intrusion have a geochemical profile typical of within‐plate A‐type granites. The pluton is enriched in high field strength elements and rare earth elements and is characterized by negative Eu anomalies in the more fractionated units. The εNd values from the two syenitic units range from +1.5 to +2.2, while the granite yields values of about +0.5. The Nd isotopic data lie below depleted mantle values but above those of the underlying Grenville crust (−2.5). Thus, the initial syenitic magma probably did not form by crustal melting but may be a mantle‐derived melt that has undergone an assimilation–fractional crystallization process. U‐Pb zircon studies of the granite unit yielded an age of 564 +10/−8 Ma, consistent with the ages of other rift‐related intrusions. Magmatism associated with the St. Lawrence River–Ottawa River Rift falls into two major periods. The first, from 615 to 588 Ma, is characterized by intrusion of mafic dike swarms of tholeiitic affinity. The second, from 577 to 554 Ma, is mostly characterized by alkaline, silica‐undersaturated intrusions with minor oversaturated syenitic intrusions, such as the Mont Rigaud Stock. Rift‐related magmatic activity ended with the extrusion of the Tibbit Hill volcanics in the Mont Sutton area of southwestern Quebec.
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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) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| 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) | 0.002 | 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 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".