Archean crustal growth and reworking in the Superior Province, Canada: Insights from whole-rock geochemistry and Nd isotopic data of the La Grande, Nemiscau and Opatica subprovinces
Bibliographic record
Abstract
The southeastern Superior Province contains Meso- to Neoarchean (2952–2677 Ma) tonalite-trondhjemite-granodiorite (TTG) suites, volcanic (2773–2703 Ma) and sedimentary (<2724 Ma) supracrustal sequences, and granitoid intrusions (2708–2598 Ma). The region is a key crustal cross-section for understanding the growth, evolution, and stabilization of Archean cratons. Whole-rock geochemistry and Nd isotopic analyses have been performed on TTG suites, volcanic assemblages and granitoid plutons of the La Grande, Nemiscau and Opatica subprovinces. These analyses, combined with existing structural and U-Pb geochronological data, have been used to investigate the extend of the basement within the three subprovinces, their interaction, and the degree of crustal reworking in the southeastern Superior Province. Nd isotope data and zircon inheritance indicate that the TTG suites were generated from: (i) an old crustal domain with Nd model ages at 3.5–3.2 Ga that may represent the southern extension of the Langelier Complex, (ii) a ca. 3.0 Ga domain with isotopically juvenile signatures, and (iii) the reworking of < 3.0 Ga Nd model age TTG suites from the Opatica subprovince. The Nd juvenile signatures of the mafic to ultramafic volcanism at ca. 2773–2756 and ca. 2723–2703 Ma suggest continuous or multiple mantle plume events beneath the southeastern Superior Province, whereas interlayered felsic volcanic rocks were formed from anatectic melting at high pressure. Subsequent magmatism was related to sanukitoid suites (2704–2693 Ma) emplacement that record mantle-TTG melt interactions. Based on a common tectonometamorphic evolution of the three subprovinces from ca. 2756 Ma, previous studies argued that the Mesoarchean TTG suites exposed in the La Grande and Opatica subprovinces represent a single crustal block. The sedimentary belts of the area were deposited in sagduction-type basins formed at ca. 2724–2706 Ma and, within less than 15–20 myr, were buried and metamorphosed up to granulite facies at 2697–2685 Ma during dip-slip-dominated D2. The burial and the following exhumation of these rocks from ca. 2677 Ma may be attributed to the delamination of lower crustal residues, favoring interaction between mantle and TTG melts, and the formation of sanukitoids and anatectic S-type granites. Nd signatures of the 2646–2598 Ma I-type granitic intrusions indicate extensively reworking of TTGs due to crustal thickening during the D3-D4 events. Our study suggests that the Archean tectonic regime recorded in the southeastern Superior Province is the result of mantle plume tectonics. We conclude that the La Grande-Opatica boundary does not represent a major suture zone but rather but rather a fossil boundary within an older extensively reworked crustal block over which the metasedimentary rocks of the Nemiscau and La Grande subprovinces were deposited.
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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 | 0.000 |
| Science and technology studies | 0.000 | 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) | 0.000 | 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".