Magmatic and Inherited Zircon Ages from a Diorite Xenolith of the Popes Harbour Dyke, Nova Scotia: Implications for Late Ediacaran Arc Magmatism in the Avalon Terrane of the Northern Appalachians
Bibliographic record
Abstract
The Meguma terrane is a unique unit of the Northern Appalachians as it is only identified in Nova Scotia. It was thrust over the Avalon terrane during the Early Devonian Acadian Orogeny. The Avalon and Meguma terranes are exotic to North America and likely originated along the margin of Gondwana. The precise relationship between the terranes is uncertain and very little is known about the basement rocks of each terrane. Hosted within the Late Devonian lamprophyric Popes Harbour dyke of the Meguma terrane are xenoliths of meta-sedimentary and meta-igneous rocks that are from the basement of the Avalon terrane. The xenoliths offer a glimpse into the nature of the lower crust of the Northern Appalachians. In this study, we present in situ zircon U-Pb age dates from a rare dioritic xenolith in order to assess its origin. The results show that the majority of zircons ages are between ~580 Ma and ~616 Ma with smaller groups at 750–630 Ma, ~2100 Ma, and <570 Ma. The zircon 206Pb/238U weighted-mean age of the rock is 603 ± 5.3 Ma and contemporaneous, with granitic intrusions of the Avalon terrane located within the Antigonish and Cobequid highlands of Nova Scotia. The diorite is compositionally similar to granitoids from an active continental margin. The discovery of Early Paleoproterozoic (~2100 Ma) zircons and the absence of Late Paleoproterozoic (1900–1700 Ma) and Mesoproterozoic (1600–1000 Ma) zircons suggests that the parental magma either encounters only Early Paleoproterozoic and Late Neoproterozoic rocks during emplacement or is derived by the melting of Paleoproterozoic rocks and/or the melting and mixing of Paleoproterozoic and Late Neoproterozoic rocks. Therefore, it is possible that Paleoproterozoic rocks may exist within the basement of the Avalon terrane.
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How this classification was reachedexpand
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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 teacher head, 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".