Syntexis and the genesis of lower oceanic crust
Why this work is in the frame
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Bibliographic record
Abstract
We propose that the term syntexis be revived and expanded to encompass all of the processes, mechanical and chemical, by which magmas react with and assimilate their host rocks. Synkinematic sills (≤50 m thick) make upthe dominant proportion of the crust of the North Arm Mountain massif of the Bay of Islands ophiolite, Newfoundland. Field, textural, and geochemical evidence implies that at North Arm, most near-monomineralic rocks (chromitites, anorthosites, and pyroxenites) are products of syntectic assimilation reactions, and a substantial proportion of wehrlites, feldspathic peridotites, and olivine gabbros are syntectic hybrids. Chromitites formed by incongruent dissolution of pyroxene or feldspar into olivine + chromite-saturated melts. Such reaction-derived chromites associated with gabbroic protoliths are systematically more aluminous than those associated with pyroxenitic protoliths; this fact suggests that the composition of the Cr-spinel in crustal chromitites at North Arm is controlled by the nature of the phases being assimilated, not by the composition of the magma. Pyroxenite and anorthosite reaction rims are interpreted to have formed through pore-scale hybridization between invading primitive magmas and partial melts of gabbroic hosts. Most feldspathic peridotites and olivine gabbros display textures suggesting that they are mixtures of invading primitive magmas and disaggregated gabbroic hosts and do not represent simple cotectic cumulates. The data from North Arm suggest that the lower ophiolitic (and oceanic) crust may act as a reactive filter and that the chemical evolution of primary magmas owes as much to assimilation and reaction with older cumulates as it does to fractional crystallization.
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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) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.005 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.032 | 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 it