Silurian mafic magmatism related to post-collisional extension, Appalachian orogen, western Newfoundland
Bibliographic record
Abstract
Gabbroic intrusions provide direct evidence of magmatic processes operating within the lithosphere and at the lithosphere–asthenosphere boundary, offering insights into magmatic differentiation, crustal growth, mantle–crust interaction, and tectonic evolution. The Taylor Brook Gabbro Suite (TBGS) is the northwesternmost expression of middle Silurian magmatism in the northern Appalachians. The petrogenesis and geochemical characteristics of the TBGS and crosscutting silicic magmatism are explored through U–Pb geochronology, mineral chemistry, lithogeochemistry, and Sr–Nd isotopic analyses, illustrating a complex history of mantle-derived mafic magmatism. The U–Pb zircon sensitive high-resolution ion microprobe ages indicate that, although the intrusive history is complex, the TBGS represents a magmatic event at 431.0 ± 2.7/4.3 Ma that was subsequently intruded by silicic magmatism at 419.7 ± 3.0/4.5 Ma. The mineral chemistry and lithogeochemistry of the TBGS suggest fractional crystallization of a magmatic system as the primary differentiation mechanism. The TBGS is tholeiitic and transitional to calc-alkaline and consists of non-arc-like, continental magmas derived from an enriched mid-ocean ridge basalt-like source. The silicic samples are granitic, magnesian, and alkali calcic in composition. The isotopic signatures of the TBGS are mostly juvenile with εNd (430 Ma) ranging from −1.1 to +6.4 and 87 Sr/ 86 Sr (i) values ranging from 0.703373 to 0.708250, with one sample having an εNd (430 Ma) of −8.6, indicating a minor role of crustal contamination by Mesoproterozoic to Neoproterozoic basement rocks. Magma ascent may have utilized inherited deep crustal structures, such as the precursor to the Doucers Valley Fault/Long Range-Cabot Fault systems. Lithospheric extension likely caused by slab rollback created a window that allowed for asthenospheric upwelling, inducing partial melting and generation of the TBGS magmas.
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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 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".