Middle Cambrian to Ordovician arc-backarc development on the leading edge of Ganderia, Newfoundland Appalachians
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Bibliographic record
Abstract
The evolution of many modern intra-oceanic and continental arc systems is exemplified by cycles of arc construction, rifting, and separation of remnant and active arcs by a backarc basin floored by oceanic crust. Rifted arc complexes and backarc basins are inherently subductable, and hence only a fragmentary record of rifting and arc construction is preserved in the ancient record. In this contribution, we synthesize available geochronological, geochemical, isotopic, and stratigraphic data in order to discuss the evolution of the Cambrian to Ordovician Penobscot-Victoria Arc, which developed on the leading edge of Ganderia, a peri-Gondwanan microcontinent. Although the Penobscot and Victoria stages of arc-backarc development occurred in a predominantly extensional suprasubduction-zone setting, they each display a distinctly different character of magmatism and sedimentation. These stages are separated by an orogenic episode marked by the obduction of backarc ophiolites onto the Ganderian passive margin. The Cambrian to Lower Ordovician Penobscot Arc is characterized by the continuous migration of the magmatic front and development of multiple volcanically active rift zones. The rift basins display a variety of characteristics, including bimodal calc-alkaline magmatism, felsic-dominated incipient rift magmatism, and formation of rifts floored by tholeiitic to boninitic suprasubduction-zone ophiolite. Comparison to modern analogues suggests that part of the Penobscot Arc area developed in a similar setting to the volcanically active Havre Trough and Taupo volcanic zone. In contrast, the Victoria Arc phase was dominated by multiple epiclastic rich, volcano-sedimentary basins overlying tectonically modified Penobscot basement. Igneous rocks are sparse, typified by calc-alkaline felsic volcanic and tholeiitic to alkaline backarc basin basalts. The change in character of the backarc volcanic rocks over time is interpreted to reflect multiple tectonic factors, including the variation of slab retreat rate, degree of extension in the arc (Cambrian Penobscot Arc) versus the backarc basin (Ordovician Exploits-Tetagouche backarc), reactivation of inverted Penobscot extensional faults during Middle Ordovician rifting, and/or depletion of fertile components by the Middle Ordovician.
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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) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.010 | 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 it