Synaccretionary sedimentary and volcanic rocks in the Ordovician Tetagouche backarc basin, New Brunswick, Canada: Evidence for a transition from foredeep to forearc basin sedimentation
Bibliographic record
Abstract
Development of an Upper Ordovician to lower Silurian (Llandovery) accretionary wedge (Brunswick subduction complex) along the composite Laurentian margin accompanied subduction of the Tetagouche backarc basin and coincided with synaccretionary sedimentation in the Bathurst and Fournier supergroups in northern New Brunswick. These dominantly turbiditic synaccretionary units conformably to unconformably overlie Upper Ordovician pelagic shale and chert in the upper stratigraphic levels of several of the nappes that compose the imbricate thrust stack of the subduction complex. Local occurrences of tectonic mélange at the contacts between the turbidites and their pelagic substrate are consistent with deposition of at least some of the former during thrust-related deformation in the accretionary wedge. Detrital zircon data indicate maximum depositional ages ranging from 454 ± 3 to 459 ± 8 Ma, coeval with initiation of subduction of the Tetagouche backarc basin. In the Elmtree inlier, arc tholeiitic basalt disconformably or unconformably overlies Darriwilian MORB-type pillowed flows that constitute backarc oceanic crust of the Tetagouche basin. Sedimentary rocks immediately below and intercalated with the arc tholeiites contain detrital zircons ranging from 444 ± 6 Ma to 455 ± 10 Ma, suggesting that the tholeiites are related to backarc subduction. Detrital zircon age spectra from all sampled units exhibit a distinct Laurentian signature, indicating an abrupt change in provenance coeval with closure of the backarc basin and Ganderia -- Laurentia collision. The lithology and implied ages of the Bathurst and Fournier synaccretionary sedimentary rocks support a correlation with siliciclastic and carbonate-rich turbidites of the Matapedia cover sequence, which were deposited farther west in a forearc setting (Matapedia forearc) with respect to subduction of Tetagouche backarc oceanic lithosphere. The implication of Late Ordovician influx onto the accretionary wedge and foredeep of sediments having a Laurentian affiliation (like those in the Matapedia forearc), demonstrates trenchward migration of forearc sedimentation between *ca.* 450 and 430 Ma. This southeastward (present coordinates) expansion occurred in concert with episodic accretion of buoyant crustal blocks that populated the Tetagouche -- Exploits basin, and concomitant southeastward step-back of the subduction zone.
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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 | 0.003 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| 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".