Delineating the lithospheric architecture of the Rae cratons using Hf and O isotopes and trace elements in zircon
Bibliographic record
Abstract
Characterizing the internal lithospheric architecture of Archean cratons is key to establishing the large-scale tectonic controls that contributed to their nucleation and formation and may play an important role in identifying the occurrence and distribution of mineral deposits. As many Archean cratons have experienced a polygenetic history, including multiple magmatic, metamorphic, and/or hydrothermal events, the primary architecture of cratonic crust may be reworked and obscured. The Rae craton in northern Canada, is no exception in that it grew through the accretion of Neoarchean (dominantly 2.58-2.75 Ga) crustal blocks followed by its amalgamation with the Slave, Hearne, and Superior cratons during <2.0 Ga Palaeoproterozoic orogenic events.Hafnium (Hf) and oxygen (O) isotopic analysis of zircon in crustal rocks has proven to be a powerful tool to elucidate crustal architecture by identifying spatial and/or temporal changes in isotopic composition that directly relate to distinct crustal age and compositional domains within a craton. Specifically, Hf isotopic data addresses the age (and compositions) of the source to igneous rocks, including degree of contamination of juvenile magmatism, while O isotope compositions monitor the extent of recycling of hydrothermally altered or weathered crust. However, systematic Hf and O isotopic data for different bedrock source terranes within Archean terranes of northern Canada is not widely available limiting the ability to refine lithospheric structures that may be preserved in the crustal column.In this study, we present preliminary in-situ U-Pb-Hf-O-trace element data from 115 Archean samples from across the Rae craton that were selected from the geochronology archive at the Geological Survey of Canada. All samples have been previously dated and were selected to cover the full spatial and temporal breadth of the craton with priority given to those preserving the highest quality zircon with the most unimodal age distributions. A small number of grains per sample were first dated by secondary ion mass spectrometry (SIMS) to confirm prior age determinations and to identify key grains for subsequent O and Hf isotope/trace element analysis by SIMS and laser ablation – inductively coupled plasma mass spectrometry, respectively. Collectively, these data will help refine petrological models of Rae crust formation, differentiate crustal domains that may or may not have experienced contrasting processes of formation, and contribute to identifying potential boundaries between isotopically different crustal blocks representing cryptic tectonic transitions within the cratons.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".