Testing the TTG–Metabasite Connection in the Southern Superior Province: an Integrated Geochemical, Isotopic, and Petrogenetic Modelling Approach
Bibliographic record
Abstract
Abstract Archean cratons are dominated by tonalite–trondhjemite–granodiorite (TTG) suites, the products of crustal differentiation that formed early continental crust. These rocks may have been primarily generated by partial melting of hydrated basaltic crust in a variety of settings including subduction zones or the deep lithosphere. Sources are mainly inferred from examination of TTGs alone, as potential source rocks are rarely exposed. In the southern Superior Province, Canada, the Kapuskasing Uplift exposes an important crustal cross-section with upper- to middle-crustal TTGs and lower-crustal metabasites, which show evidence of having produced trondhjemitic anatectic melt. Here, we test the hypothesis that these metabasites were the source of the Mesoarchean to Neoarchean TTGs in the Kapuskasing Uplift by combining phase equilibrium and melt trace element modelling with whole-rock and zircon Lu–Hf isotope analysis and geochronology (garnet Lu–Hf and zircon U–Pb) of metabasic samples. By comparison of the results with existing data from TTGs in the Kapuskasing Uplift, we determined that the metabasites are plausible source rocks for the TTGs. The Lu–Hf systematics of the metabasites and TTGs are the most robust evidence of a genetic connection. Modelling results support an increase in TTG source depth over time. New geochronological data constrain partial melting of metabasite and crystallization of anatectic melt between ca. 2685 Ma and ca. 2600 Ma, coeval with crystallization of only the youngest TTGs. Overall, these results indicate a complex history of intracrustal differentiation in the Kapuskasing Uplift, with partial melting of two isotopically distinct lower-crustal metabasic sources at different times and depths.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 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 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".