Geochemical constraints on the petrogenesis of Eocene volcanic rocks from the Terrace Mountain volcanic complex, south-central British Columbia: Tectonic implications
Bibliographic record
Abstract
ABSTRACT The Terrace Mountain volcanic complex in south-central British Columbia is hosted in an elongated half graben, which is >40 km long and 2–4 km wide. The volcanic pile, ~900 m thick, is part of a discontinuous Eocene volcanic chain that stretches in a north-northwest direction for >2000 km from the northwestern United States to the interior of central British Columbia. The volcanic chain is made up mainly of high- to medium-K calc-alkaline rocks, typical of rifted continental margin arcs. The rocks were emplaced during a time of regional transtensional tectonics in the North American Cordillera. The Terrace Mountain complex extruded within a short magmatic episode ca. 52 Ma in four distinct magmatic pulses. The rocks are unusually diverse in their isotopic composition relative to other volcanic complexes of the chain. Two older pulses, which are composed of basanites, trachybasalts, basaltic trachyandesite, and trachyandesite (with negative εNd[t] and high initial 87Sr/86Sr values), were derived from a parent magma that was sourced from subduction-modified subcontinental lithospheric mantle enriched during the Proterozoic, like volcanic rocks of the part of the chain that overlies ancestral cratonal North America. The overlying third pulse is composed of rhyolitic rocks, which were derived from heterogeneous continental crust by partial melting triggered by an intrusion of the mafic magma. Compared to the underlying mafic and intermediate rocks, the youngest pulse, composed of basaltic trachyandesite and trachyandesite, was derived from an isotopically different source (with positive εNd[t] and low 87Sr/86Sr values), enriched during the early Paleozoic, like many other volcanic rocks of the belt that lie on top of the Intermontane superterrane. These geochemical characteristics suggest that the parent magmas of the three pulses composed of mafic and intermediate rocks were formed by slab failure (slab break-off) at a subduction zone, where the rising asthenospheric mantle initiated melting.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.003 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.002 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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".