Mafic sills in the Meguma terrane, southwestern Nova Scotia, Canada: petrology, tectonic setting, and ages
Bibliographic record
Abstract
In the western part of the Meguma terrane from Wolfville to Yarmouth the Cambrian to Silurian Goldenville, Halifax, and Rockville Notch groups are intruded by mafic sills. The sills are divided into type I and type II based on field relations, textures, and alteration. Type I sills are likely contemporaneous with their host rocks and display vesicular or pepperitic textures near convolute top margins, making them ideal way-up indicators for the host sedimentary rocks. They are usually 1–5 m wide and are folded with their host rocks. They also have more extensive carbonate, and silicic alteration than type II sills. The type II sills are much thicker (up to 100 m) having sharp contacts on the top and bottom margins and have less alteration containing intact clinopyroxene. The two types of sills have similar geochemical signatures, and all were formed in a within-plate environment with compositions that are mainly alkalic. Chemical analyses of about 120 samples show a range in SiO2 from about 35% to 51% with Fe2O3 Total from 9% to 16%, MgO from 3% to 11%, and CaO from 2% to 11% (CaO > MgO for all samples). Alteration is variable as shown by LOI values ranging from 1% to 15% and Sr values of 250–1300 ppm which suggest extensive fluid migration and alteration, complicating the use of chemical data in these sills. Additional geochemical analysis with trace element and rare earth element may reveal subtle differences between sills. Laser ablation ICP-MS U–Pb analysis indicate that the Type 1 sills cooled through apatite closure (350 - 500°C) at ca. 430 Ma ± 71 which is broadly consistent with previous interpretations that they formed penecontemperaneously with their host rocks but the exact age is still unknown because of the large error range.
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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 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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".