Comparisons Between Tethyan Anorthosite‐Bearing Ophiolites and Archean Anorthosite‐Bearing Layered Intrusions: Implications for Archean Geodynamic Processes
Bibliographic record
Abstract
Abstract Elucidating the petrogenesis and geodynamic setting(s) of anorthosites in Archean layered intrusions and Tethyan ophiolites has significant implications for crustal evolution and growth throughout Earth history. Archean anorthosite‐bearing layered intrusions occur on every continent. Tethyan ophiolites occur in Europe, Africa, and Asia. In this contribution, the field, petrographic, petrological, and geochemical characteristics of 100 Tethyan anorthosite‐bearing ophiolites and 155 Archean anorthosite‐bearing layered intrusions are compared. Tethyan anorthosite‐bearing ophiolites range from Devonian to Paleocene in age are variably composite, contain anorthosites with highly calcic (An44–100) plagioclase and magmatic amphibole. These ophiolites formed predominantly at convergent plate margins, with some forming in mid‐ocean ridge, continental rift, and mantle plume settings. The predominantly convergent plate margin tectonic setting of Tethyan anorthosite‐bearing ophiolites is indicated by negative Nb and Ti anomalies and magmatic amphibole. Archean anorthosite‐bearing layered intrusions are Eoarchean to Neoarchean in age, have megacrystic anorthosites with highly calcic (An20–100) plagioclase and magmatic amphibole, and are interlayered with gabbros and leucogabbros and intrude pillow basalts. These Archean layered intrusions are interpreted to have predominantly formed at convergent plate margins, with the remainder forming in mantle plume, continental rift, oceanic plateau, postorogenic, anorogenic, mid‐ocean ridge, and passive continental margin settings. These layered intrusions predominantly crystallized from hydrous Ca‐ and Al‐rich tholeiitic magmas. The field, petrographic, and geochemical similarities between Archean and Tethyan anorthosites indicate that they were produced by similar geodynamic processes mainly in suprasubduction zone settings. We suggest that Archean anorthosite‐bearing layered intrusions and spatially associated greenstone belts represent dismembered subduction‐related Archean ophiolites.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".