Geochemistry and SrNd isotopic composition of Eocene lamphrophyre dykes, southeastern British Columbia
Bibliographic record
Abstract
Mineral compositions, geochemical analyses, and SrNd isotopic compositions are reported for alkaline and calc-alkaline lamprophyres collected along the southern margin of the Valhalla Complex, southeastern British Columbia. The lamprophyres were emplaced during Eocene extension and lithospheric thinning associated with tectonic denudation of the Valhalla Complex. SiO2 contents range from 44.451.6 wt.%, K2O from 1.33.7 wt.%, and volatile contents (H2O + CO2 + SO3) from 0.84.6 wt.%. MgO and Cr contents are 9.57.6 wt.% and 540130 ppm, respectively, for samples with Mg#s between 0.69 and 0.65. Chrondrite-normalized rare-earth element patterns are strongly fractionated with Cen = 120375 and Ybn = 8.412.7. Alkaline lamprophyres contain biotite ± kaersutite ± calcic plagioclase and exhibit a limited range in initial 87Sr/86Sr (0.70510.7057), initial εNd (3.7 to 4.3), and TDM (766796 Ma). Calc-alkaline lamprophyres contain F-rich phlogopite and sodic plagioclase, and exhibit a wider range in initial 87Sr/86Sr (0.70640.7090), initial εNd (6.3 to 11.9), and TDM (9171,614 Ma). Alkaline lamprophyres are interpreted as uncontaminated melts derived from a long-term, volatile, and incompatible element-enriched mantle reservoir. Mantle enrichment coincided with continental rifting of western North America (ca. 760 Ma). The enriched mantle reservoir remained isolated for ~700 Ma. Lamprophyres were generated by partial melting of the mantle reservoir in response to adiabatic decompression and lithospheric thinning during Eocene extension.
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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 | 0.002 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 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 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".