Precambrian lithospheric structure and evolution: evidence from broadband seismology in Eastern Canada
Bibliographic record
Abstract
The thick and seismically fast Precambrian continental remnants (cratons) provide fundamental clues about the tectonic processes that operated on the early Earth. Eastern Canada is a natural laboratory to study such processes: its geological record spans more than 3 Ga of Earth history, including the assembly of the largest Archean craton in the world, the Superior craton, which is surrounded by global scale Proterozoic and Phanerozoic orogenic belts. To investigate the crustal and lithospheric structure of eastern Canada, earthquake data recorded at a new broadband seismic network were analysed, in conjunction with other permanent and temporary networks. The QM-III (Quebec-Maine Across Three Sutures) network was deployed across the main tectonic boundaries in eastern Canada, extending from Hudson Bay to the Atlantic Ocean. Using Hk stacking and probabilistic inversion of receiver functions, bulk crustal composition (Vp/Vs ratio), crustal thickness and shear wavespeed (Vs) were estimated beneath seismic stations. Post- Archean crust is thicker ( ~40 km), faster (dVs ~ 0.2 km/s), more heterogenous and more ma c (Vp/Vs ~1.76), suggesting increased crustal growth efficiency, possibly stimulated by mafic underplating. Lack of correlation between Moho topography, elevation and gravity anomalies in Proterozoic terranes indicate isostatic imbalance, best explained by strong mantle buoyant support. An anisotropic seismic model of the Precambrian lithosphere was constructed using fundamental mode Rayleigh waves. Phase velocity heterogeneity and azimuthal anisotropy patterns reveal multiple lithospheric layers within the Superior craton, with distinct tectonic origins. The upper lithosphere is seismically fast ( ~2%) and preserves Archean fossil anisotropy ( ~1%), implying that plate-scale deformation occured during the Archean. This layer partially extends beneath the adjacent Proterozoic belt and survived subsequent metasomatism. The lower lithosphere is fast ( ~2%), more homogenous and weakly anisotropic (<0.5%), documenting post assembly lithospheric growth in a slow convection regime. Cratonization processes may be episodic and are not exclusively an Archean phenomenon.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.008 | 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".