Mesoproterozoic Oaxaquia-type basement in peri-Gondwanan terranes of Mexico, the Appalachians, and Europe: <i>T</i> <sub>DM</sub> age constraints on extent and significance
Bibliographic record
Abstract
The basement of most peri-Gondwanan terranes in Mexico, the Appalachians, the Caledonides, and the Variscides is buried beneath younger Ediacaran arc, Palaeozoic passive margin, and/or Mesozoic–Cenozoic platformal carbonates. However, it is exposed in the Oaxaquia terrane of Mexico (Oaxacan, Novillo, Huiznopala, and Guichicovi complexes), where it is characterized by ca. 1.0–1.3 billion year protolith ages and igneous rocks with depleted mantle model ages (T DM) of 1.35–1.77 billion years. The T DM ages represent a bulk average composition of the source and can be used as a tracer; these T DM ages overlap with those in ca. 546 Ma arc clasts from the 65.5 Ma Chicxulub bolide breccia, suggesting that the northern Maya block is also underlain by Oaxaquia-type basement. Similar T DM ages occur in Ediacaran arc rocks in Suwannee (Florida), NW Avalonia, Ganderia, Iberia, Armorica, and Bohemia, and in lower Palaeozoic plutons cutting adjacent Palaeozoic passive margin rocks (Acatlán Complex, Gander Group), suggesting that Oaxaquia-type basement underlies these regions. These T DM ages are intermediate between those of SE Avalonia/Carolinia (0.75–1.1 billion years) and the ca. 2.0 Ga basement typical of NW Africa and the Channel Islands of the United Kingdom. The lateral extent of this Oaxaquia-type basement suggests that it formed a Precambrian rim around the periphery of northern Gondwana (Amazonia and NW Africa). The Oaxaquia-type basement beneath Ganderia and northwestern Avalonia suggests that these terranes were derived from the Oaxaquia margin of Amazonia. The polarity of the T DM ages in Avalonia (younger to the SE) suggests that, rather than being transferred orthogonally across Iapetus, these peri-Gondwanan terranes rotated clockwise through ∼90° before accretion to Laurentia.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".