Crustal evolution of the Laurentian continental margin from the Paleo- through Mesoproterozic: A zircon U–Pb and Hf transect through the western Grenville Province, Ontario, Canada
Bibliographic record
Abstract
The Great Proterozoic Accretionary Orogeny along the southern and southeastern margin of Laurentia is arguably the first long-lived, modern-style active plate margin on Earth, representing significant crustal growth and reworking. Here, we present new detrital zircon U–Pb and Hf data, along with zircon and monazite metamorphic ages, from tectonic domains in the southwestern Grenville Province that represent depositional basins formed and reworked during a series of events between 2.2 and 1.2 Ga. As such, the data allow a glimpse into the evolution and assembly of this extensive margin. The Nepewassi domain contains Archean basement overlain by mature sandstone characterized by near-unimodal, ca. 2.7–2.6 Ga detrital zircon peaks and likely correlative with Superior Province basement and its Huronian cover. The Nepewassi domain underwent both Archean (ca. 2.65 Ga) and Killarnean (ca. 1.76 Ga) metamorphism. In addition, all units preserve evidence of Grenvillian high-grade metamorphism between ca. 1.05 and 0.99 Ga. The structurally highest parts of the Nepewassi domain also contain younger sedimentary rocks that received detritus from Killarnean sources, with evolved Hf isotopic compositions indicative of reworked Archean crust. Sedimentary rocks in the Tomiko domain preserve detrital zircon of Penokean and Killarnean age (1.9–1.7 Ga) with evolved Hf compositions, along with Labradorian (1.7–1.6 Ga) grains of more juvenile composition. Detrital zircon from the Kiosk domain yield Penokean through Labradorian ages, with Hf compositions ranging from evolved to juvenile. In contrast to the sedimentary rocks found in these Laurentia-derived parautochthonous domains, similar rocks from younger, more allochthonous units, including the Shawanaga and basal Parry Sound domain, dominantly contain zircon ranging from Pinwarian (ca. 1.45 Ga) through ca. 1.20 Ga that show exclusively juvenile isotopic compositions. The data show that sedimentary basins received detritus from nearby active sources as well as from the nearby Superior continent, and that successively younger sources and basins became increasingly less influenced by continental input as the margin grew wider. The data add to a growing database of similar data from other parts of this several thousand-kilometer-long margin that seemingly displayed little along-strike variation in overall evolution, implying the existence of a vast, Pacific-scale ocean.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 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) | 0.002 | 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 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".