2.4–2.3 Ga granitoids of the Arrowsmith orogeny, southwestern Rae craton, Canada: Syn- and post-orogenic magmatism during a global tectono-magmatic lull
Bibliographic record
Abstract
Constraints on the tectonic and magmatic processes that occurred during the 2.4–2.2 Ga tectono-magmatic lull are limited by the relative paucity of 2.4–2.2 Ga magmatic rocks available for study. One place with a substantial record of 2.4–2.3 Ga magmatism is the western Rae craton. We present whole-rock geochemical and Nd isotope data, and zircon U-Pb-Hf isotope and trace-element data for granitoids in an understudied portion of the southwestern Rae craton. Two groups of granitoids are documented, ca. 2.43–2.38 Ga leucogranitoids and ca. 2.32–2.31 Ga biotite granites. All of the granitoids are peraluminous and silica rich (>69 wt% SiO 2 ), and have negative initial εNd and εHf values. The ca. 2.43–2.38 Ga leucogranitoids have comparatively low high-field strength element contents, zircon saturation temperatures (677–828 °C) and Ti-in-zircon temperatures (medians = 707–798 °C), and some of them contain abundant inherited zircon. Their generation was in part coeval with ca. 2.38 Ga migmatization of local metasedimentary and mafic metaigneous rocks. The ca. 2.32–2.31 Ga granites have elevated high-field strength and light rare earth element contents, relatively high zircon saturation (785–905 °C) and Ti-in-zircon (medians = 724–899 °C) temperatures, strongly negative initial εNd (−5 to −11) and εHf (−10 to −18) values, and little-to-no inherited zircon. These granites were produced via high-temperature (>900 °C) melting of tonalitic-granodioritic rocks, including a significant proportion > 3.0 Ga rocks that must be widespread at depth in the study area. Evidence of ca. 2.35–2.30 Ga mafic magmatism that could have supplied heat for this high-temperature melting has not been identified in the study area, but has been documented elsewhere in the western Rae craton. We propose that the ca. 2.43–2.38 Ga leucogranitoids reflect anatexis in response to one or more episodes of collisional orogenesis and the ca. 2.32–2.31 Ga granites formed in a post-orogenic setting. Comparisons with ca. 1.85–1.75 Ga syn- and post-orogenic granitoids associated with the Trans-Hudson orogen support these tectonic interpretations and indicate that the 2.4–2.3 Ga granitoids were produced through “modern-style” tectonic processes, similar to those that occurred during the Trans-Hudson orogeny.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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 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".