Structural and thermal evolution of an infant subduction shear zone: Insights from sub-ophiolite metamorphic rocks recovered from Oman Drilling Project Site BT-1B
Bibliographic record
Abstract
The thermal structure of the subduction interface changes drastically within the first few million years following subduction initiation (i.e. subduction infancy ), resulting in changing metamorphic conditions and degree of mechanical coupling. Metamorphic soles beneath ophiolites record snapshots of subduction infancy. Beneath the Samail Ophiolite (Oman), the sole comprises structurally higher high-temperature (HT) and lower low-temperature (LT) units. This apparent inverted metamorphic gradient has been attributed to metamorphism under different Pressure-Temperature (P-T) conditions along the interface. However, peak P-T and timing of LT sole subduction are poorly constrained. Samples from Oman Drilling Project core BT-1B (104 m of metamorphic rocks) reveal that the LT sole subducted to similar peak P as the HT sole, but experienced ~300˚C lower peak T. Prograde fabrics in meta-sedimentary and meta-mafic rocks record Si-in-phengite values and amphibole chemistries consistent with peak P-T of ~8-12 kbar and ~450-550˚C in the epidote-amphibolite facies. Retrograde fabrics record a transition from near pervasive ductile to localized brittle strain under greenschist facies conditions. Titanite U-Pb ages (two samples) constrain timing of peak LT sole subduction to 95.7 ± 1.1 Ma, which may post-date the HT sole by ~6-8 Myr. In light of previous HT sole thermobarometry and geochronology, these new results support a model of protracted subduction and accretion while the infant subduction zone cooled at rates of ~100˚C/Myr for ~1-5 Myr. Temporal overlap of LT sole metamorphism and ophiolite crust formation suggests that underthrusting and cooling may lead to interface weakening, facilitating upper plate extension and forearc spreading.
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".