Eoarchean–Paleoproterozoic Tectonothermal History of the Acasta Gneiss Complex Constrained by Titanite and Apatite Petrochronology
Bibliographic record
Abstract
Abstract Deciphering Earth's earliest geodynamic processes requires temporally constrained chemical and structural data from rare exposures of ancient rocks. One of the most well‐studied of these exposures is the Acasta Gneiss Complex (AGC) in the Northwest Territories, Canada, which contains the oldest known felsic rocks on Earth. Like other Archean terranes, the AGC has experienced billions of years of magmatism, metamorphism, and deformation, which make it difficult to tie chemical and structural information to specific events. To construct a reliable tectonothermal history, U‐Th‐Pb isotope and trace‐element data from titanite and apatite were collected from two mafic amphibolites and four felsic‐intermediate gneisses along a regional traverse through the AGC. The U‐Th‐Pb isotope data are augmented by petrography, backscattered electron and X‐ray element maps, and trace‐element compositions to better contextualize the polymetamorphic history preserved in these phases. Titanite records multiple metamorphic stages from ≥3.6 to 1.9 Ga, whereas apatite only preserves 1.9 Ga metamorphism. The ubiquity of ∼2.9 Ga titanite growth at amphibolite‐facies or higher temperatures suggests widespread metamorphism in response to early tectonism. Partial to complete recrystallization of titanite and apatite at ∼1.9 Ga in the AGC is coeval with metamorphism during the Calderian orogeny. The preservation of Archean titanite in most samples suggests that the influence of the Calderian orogeny was not pervasive across the AGC. Our accessory phase petrochronologic data present a more complete geologic history for the AGC and inform models for early Earth geodynamics, formation of cratons, and the evolution of tectonics in the Slave craton.
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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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".