‘Subduction Style’ Magmatism in a Non-subduction Setting: the Colville Igneous Complex, NE Washington State, USA
Bibliographic record
Abstract
The Colville Igneous Complex is located within the Eocene Magmatic Belt of the North American Cordilleran interior. It straddles the US–Canadian border in northeast Washington and southern British Columbia. The complex consists of three intrusive and two extrusive phases, the first extrusive phase being contemporaneous with the latter two intrusive phases. As a consequence of sub-solidus re-equilibration in the plutonic rocks, this study concentrates on the two extrusive phases, the Sanpoil Volcanic Formation and the Klondike Mountain Formation. The Sanpoil Volcanic Formation consists of andesites, dacites and rare trachyandesites (SiO2 = 55–70 wt %) exhibiting a slight decrease in total alkalis (Na2O + K2O) with increasing silica. The Klondike Mountain Formation consists of basalts, basaltic andesites, andesites, dacites and rhyolites (SiO2 = 51–75 wt %) with total alkalis increasing with increasing silica. The calc-alkaline affinity of the rocks of the Colville Igneous Complex, coupled with the presence of a 'subduction signature' of enriched large ion lithophile elements (LILE) and depleted high field strength elements (HFSE), has traditionally been attributed to petrogenesis in a subduction-related magmatic arc, the 'Challis Arc'. New trace and rare earth element and isotopic data (87Sr/86Sri, ϵNdi, δ18O), however, suggest that this explanation is no longer tenable. We propose that the magmas of the Sanpoil Volcanic Formation were generated by mid-crustal partial melting of a mid-Proterozoic source and that the Klondike Mountain Formation was formed by varying degrees of mixing between two distinct late-Proterozoic lower-crustal sourced magmas and a mantle-derived magma. In all cases, the subduction or calc-alkaline signature was inherited from the Proterozoic crustal sources. The only magmas that can confidently be attributed to a mantle source are the basalts of the Klondike Mountain Formation, which show no decoupling of the LILE and HFSE, i.e. no subduction signature, precluding the presence of a subduction slab beneath this part of the North American Cordillera during the Eocene. We propose the alternative model: that the Colville Igneous Complex formed as a result of decompression melting of crust and mantle during post-Laramide orogenic collapse of an overthickened crust.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 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".