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| Boukari Shear Zone | |
|---|---|
| Name | Boukari Shear Zone |
| Type | Shear zone |
| Location | West Africa |
| Region | West African Craton |
| Country | Burkina Faso; Ghana; Mali (contested) |
| Age | Paleoproterozoic to Neoproterozoic (see text) |
| Lithology | Metasedimentary rocks; granitoids; mafic dykes; migmatite |
| Orogeny | Eburnean; Pan-African |
Boukari Shear Zone is a major crustal-scale ductile shear zone within the western segment of the West African Craton that juxtaposes Archean to Proterozoic terranes and controls regional metamorphic gradients, magmatism, and mineral systems. It forms a northeast–southwest to east–west corridor that links basins, belts, and plutonic bodies across parts of Burkina Faso, Ghana, and western Mali. The zone is a locus for mapped structures, isotopic anomalies, and exploration efforts by national geological surveys and mining companies.
The Boukari corridor transects the Man Shield, the Birimian greenstone belts, and adjacent Sassandra and Leo-Man Shield fragments, slicing through metavolcanic, metasedimentary, and granitoid assemblages recognized by the British Geological Survey, Geological Survey of Ghana, and Bureau des Mines du Burkina Faso. It lies proximal to major terrane boundaries such as the Southeast Nigerian Shield junction and the Taoudeni Basin margin, and intersects Paleoproterozoic orogenic belts correlated with the Eburnean orogeny and later reactivated during the Pan-African orogeny. Regional stratigraphy includes sequences comparable to those in the Ghanaian Shield, Hounde Group, and Volta Basin margins.
The zone exhibits a composite fabric of mylonites, ultramylonites, and associated brittle-ductile faulting documented by field teams from Université de Ouagadougou, University of Ghana, and Université de Bamako. Structural elements include S-C fabrics, asymmetric folds, and shear-related foliations linked to sinistral and dextral kinematics measured using methods similar to those applied in Vredefort and Kibaran studies. The Boukari system connects to cross-cutting shear corridors analogous to the West African shear network and shows transpressional geometries comparable to the Great Glen Fault and the Leinster Granite margin in scale and complexity.
Geochronological work using U–Pb zircon, Sm–Nd isotopes, and Ar–Ar thermochronology by teams from BRGM, US Geological Survey, and university laboratories indicates multiple deformational pulses: an Early to Middle Paleoproterozoic phase contemporaneous with the Eburnean orogeny (~2.1–2.0 Ga) and a late Neoproterozoic reactivation during the Pan-African orogeny (~0.6–0.5 Ga). Detrital zircon populations show provenance links to the Transamazonian and West African Craton margins, and isotopic signatures comparable to rocks from Birimian successions and Taoudeni sequences, supporting models of arc accretion, collision, and subsequent strike-slip transfer between major cratonic blocks.
Metamorphic grades across the shear zone range from greenschist to amphibolite and locally granulite facies, with migmatization and partial melting documented in granitoid-hosted mylonites by petrographers from Université de Liège and University of Cambridge. Mineral assemblages include quartz + muscovite + biotite ± garnet ± kyanite, comparable to assemblages reported from the Sierra Leone Shield and Liberian domains. Petrographic studies note syn-tectonic leucogranites, synkinematic garnet growth, and textural evidence for fluid infiltration similar to patterns described in Kibali-type shear-hosted systems.
The Boukari corridor is a target for exploration by multinational miners such as AngloGold Ashanti, Barrick Gold, and junior companies active in the Birimian belts, owing to gold mineralization, structurally controlled quartz-vein systems, and associated sulfide concentrations. Documented commodities include orogenic gold, base metals (lead, zinc), and rare accessory minerals analogous to deposits in the Ashanti Belt, Prestea, and Tarkwa districts. Mineralization types reflect orogenic, mesothermal, and structurally remobilized models familiar from Witwatersrand-analog studies, and are assessed in national strategic plans by Chamber of Mines of Burkina Faso and Ghana Chamber of Mines.
Airborne magnetics, gravity surveys, and passive seismic experiments conducted by consortia including CGG, GEOSCAN, and national surveys have imaged linear anomalies, crustal-scale shear zones, and lithological contrasts along the Boukari trend. Geophysical signatures show steeply dipping magnetic gradients and gravity lows consistent with felsic plutons and mylonitic zones; magnetotelluric profiles reveal conductivity anomalies comparable to those beneath the Kibaran Belt and Damara Orogen. Remote sensing and Landsat-guided mapping by teams from NASA and ESA support field-based geological maps produced in collaboration with the International Union of Geological Sciences initiatives.
Early regional recognition of the corridor derives from colonial-era mapping by the Geological Survey of Ghana and French expeditions associated with IFAN and ORSTOM. Key modern contributions include U–Pb zircon syntheses by laboratories at Stanford University and Université de Paris, structural syntheses published in journals where authors affiliated with University of Johannesburg, University of Montpellier, and University of Calgary compared Boukari fabrics to global shear zones. Ongoing work integrates isotopic, petrological, and geophysical datasets under cooperative projects funded by entities such as the World Bank mineral sector programs and bilateral research grants involving CNRS and regional universities.
Category:Geology of West Africa Category:Shear zones