Petrology of the early Neoproterozoic Bou Azzer–El Graara Tachdamt–Bleida igneous formations (Central Anti-Atlas, Morocco): geodynamic evidence for NW Gondwana
Bibliographic record
Abstract
The Tachdamt and Bleida formations from the Bou Azzer–El Graara inlier (Central Anti-Atlas, Morocco) record two distinct Neoproterozoic magmatic episodes that were previously grouped as a single unit. In this study, we present new whole rock major and trace elements geochemistry alongside samarium-neodymium (Sm-Nd) isotopic data for representative volcanic and volcano-sedimentary rocks from both formations. Uranium-lead (U-Pb) zircon dating from previous studies confirms emplacement ages of ~883 Ma for the Tachdamt Formation and ~700 Ma for the Bleida Formation. The temporal separation and geochemical distinctions between these formations demonstrate two independent magmatic events. The ~883 Ma Tachdamt Formation coincides in age with the Munali magmatism (~880–860 Ma) in the Greater Congo Craton; although a direct geodynamic link remains uncertain, this age similarity suggests both events formed during a broader Neoproterozoic extensional phase. Geochemical signatures further differentiate the two pulses. The Tachdamt basalts exhibit tholeiitic affinities, high iron-titanium (Fe-Ti) contents, enrichment in LILE, and positive neodymium isotopic values [εNd(t) = +3.2 to +4.5], consistent with plume-related magmatism in a Tonian large igneous province (LIP). In contrast, the Bleida basalts display negative niobium (Nb) anomalies, greater geochemical variability, and older depleted mantle model ages (TDM = 1.1–1.3 Ga), indicating an arc-influenced lithospheric mantle source in a foreland basin setting. These contrasting signatures record a geodynamic transition from extensional, plume-driven rifting (Tachdamt) to subduction modified magmatism (Bleida) along the northwestern margin of the West African Craton (WAC). Additional dolerite dykes crosscut both formations, marking a younger magmatic phase and exhibiting orientations similar to the ~860 Ma Manso dyke swarm; further U–Pb dating is required to clarify their provenance. Overall, our new geochemical and isotopic dataset refines the Neoproterozoic tectonic evolution of the Anti-Atlas and provides critical constraints on the broader magmatic and rheological history of Rodinia’s break-up.
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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 | 0.001 |
| 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 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".