Iron-rich alkaline magmatism in the Archean Schreiber-Hemlo greenstone belt, Ontario, Canada
Bibliographic record
Abstract
The finding of Fe-rich picritic basalts in the Gusev Crater on Mars has stimulated interest in Fe-rich magmatism on the early Earth. A significant number of occurrences of ferropicrite magmatism have been identified in Archean terranes, and a study of their mineralogy and setting may provide insights into the petrogenesis of Martian ferropicrites. One of the best exposed of these terrestrial ferropicrites occurs in the Pulpwood Harbour sequence of the Heron Bay volcanics (~2.6-2.7Ga) in the Schreiber-Hemlo Greenstone Belt of the Superior Province of Canada. The ferropicrite bodies consist largely of cumulate rocks, overlain by minor Fe-rich lavas. The compositions of the cumulate rocks can be explained by progressive crystal accumulation of olivine (~Fo76) followed by clinopyroxene and then Fe-Ti oxides, in a relatively closed system, and with increasing proportions of interstitial liquid contained in the cumulate rocks. The overlying Fe-rich lavas represent very Fe-rich liquids, with up to ~17 wt.% FeO*, which appear to be comagmatic with the cumulate rocks below them. Although the compositions of the chilled margins and the Fe-rich lavas are similar to those of Martian lavas from Gusev crater, the Pulpwood Harbour ferropicrites liquids appear to have been mildly Silica-undersaturated, in contrast to the strongly orthopyroxene- normative compositions of the Gusev Crater ferropicrites, and have enriched incompatible trace element profiles characteristic of modern mildly alkaline OIB-type basalts. Inconsistencies between trace elements and major element modeling suggest, however, that the original parental magma may have had a significant carbonate component that was largely lost from the volcanic rocks upon eruption, but partially retained in the cumulate ferropicritic rocks of Pulpwood Harbour.
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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 | 0.003 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.001 | 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".