Timing of ophiolite obduction in the Grampian orogen
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Bibliographic record
Abstract
This study addresses the timing and pressure-temperature (P-T) conditions of ophiolite obduction, one of the proposed causes of the ca. 470 Ma Grampian orogeny of Scotland and Ireland. This event gave rise to the main structural and metamorphic characteristics of the Grampian terrane-the type area for Barrovian metamorphism, the cause of which remains enigmatic despite a century of research. Zircons from the Highland Border ophiolite, Scotland, define a 499 ± 8 Ma U-Pb concordia age, which is interpreted as dating magmatism. Its metamorphism is dated by a 490 ± 4 Ma 40Ar-39Ar hornblende age, and a 488 ± 1 Ma 40Ar-39Ar muscovite age from a metasedimentary xenolith within it, from which P-T estimates of 5.3 kbar and 580 °C relate to ophiolite obduction. Meta-morphism of the Deerpark complex ophiolitic mélange (Irish correlative of the Highland Border ophiolite) is constrained by a 514 ± 3 Ma 40Ar-39Ar hornblende age, while mica schist slivers within it yield detrital zircon U-Pb ages consistent with Laurentian provenance and Rb-Sr and 40Ar-39Ar muscovite ages of ca. 482 Ma. P-T values of 3.3 kbar and 580°C for the mica schist constrain the conditions of ophiolite obduction. Metamorphic mineral ages from the Grampian terrane (Dalradian Supergroup) are substantially younger (ca. 475-465 Ma) than those from the ophiolites. If conductive heating in overthickened crust was the cause of Barrovian metamorphism, then collisional thickening must have started soon after ophiolite obduction at ca. 490 Ma in order to generate the ca. 470 Ma metamorphic peak in the Grampian terrane. © 2010 Geological Society of America.
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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) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.019 | 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