U-Pb and Lu-Hf LA-ICP-MS detrital zircon and structural investigations in the Abitibi subprovince, Canada, with implications for Archean geodynamic processes and deformation behavior along gold-bearing, crustal-scale faults
Bibliographic record
Abstract
This work presents investigations based in the south-central Abitibi subprovince of Ontario and Quebec, Canada, which place constraints on a sequence of Neoarchean geodynamic and structural processes, including crustal growth and amalgamation with the rest of the Superior Province, and the formation of orogenic gold deposits along regional deformation zones.Archean geodynamic processes were primarily investigated by multi-isotope U-Pb and Lu-Hf laser ablationinductively coupled plasmamass spectrometry (LA-ICP-MS) analysis of detrital zircon grains from successor basins.Three temporally distinct successor basin groups are recognized: the ~2690-2685 Ma Porcupine assemblage, the ~2685-2682 Ma Pontiac subprovince, and the ~2680-2670 Ma Timiskaming assemblage.All samples contain abundant Neoarchean grains (~85-95% of the individual sample populations), while the remaining grains yielded Mesoarchean ages.The Neoarchean grains likely reflect predominately local sources.Since no Mesoarchean rocks occur in the Abitibi and Pontiac subprovinces, and based on comparison with published zircon ages from the Superior Province,Mesoarchean grains are interpreted as derived from an orogenic hinterland to the NNW that developed during regional amalgamation.The older Porcupine assemblage contains ~5% Mesoarchean zircon, while Pontiac subprovince and Timiskaming assemblage samples contain ~18% and ~13%, respectively.This suggests hinterland sources were more prevalent during the late stages of collision, probably as a result of progressive uplift and denudation of the hinterland.The paired Lu-Hf isotopic analyses support this interpretation of provenance and further indicate that the majority of grains (~96%) have compositions consistent with derivation from a modern MORB depleted mantle (mMORB-DM) reservoir.This occurrence of mMORB-DM-like signatures in detrital zircon grains that were sourced from multiple disparate crustal domains suggests that a modern-style depleted mantle reservoir was not only well established, but widely occurring by the Mesoarchean.The observed pattern of lateral accretion of crustal domains that grew from a mMORB-DM-like reservoir, the transport of detritus across terrane boundaries, and the progressive uplift and denudation of a hinterland are most consistent with the operation of plate tectonic processes during Neoarchean construction and amalgamation of the southern Superior Province.During the late stages of accretion, deformation became increasingly localized along regionally extensive, crustal-scale fault zones, including the Larder Lake Cadillac deformation zone (LLCdz) in the Kirkland Lake area of Ontario.New field mapping and map compilation indicates that a series of spaced brittle-ductile deformation zones occur in a broad, >6 km area to the north of the LLCdz.Detailed structural mapping and analysis further indicate that the location of late-stage brittle-ductile deformation, fluid flow, and iv gold mineralization was likely controlled by early brittle deformation zones characterized by breccia.Therefore, undiscovered gold deposits may be hosted by deformation zones farther from the LLCdz than previously recognized and that fault-related breccia bodies may provide an indicator for nearby prospective structures in both the Kirkland Lake area and in similar structural settings of all ages, worldwide.
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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 | 0.003 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".