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Title: Evolution of the early Proterozoic Boundiali-Bagoe Supracrustal Belt and associated granitic rocks, northern Cote d'Ivoire, West Africa.
Author: Turner, Peter.
Awarding Body: University of Portsmouth
Current Institution: University of Portsmouth
Date of Award: 1995
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The ca. 2.1 Ga Boundiali-Bagoo Supracrustal Belt is situated in the BaouM-Mossi domain of the West African craton. The belt is composed of greenschist facies metavolcanics and metasediments which comprise the Bagoo River Supergroup (BRS). It occurs in sheared contact with syn-tectonic granitic gneisses and granites to the west (the Dyogo Granite Complex - DGC) and is intruded by syn- and post-orogenic granitoids. Some 3,OOOkm2 of supracrustal and granite terrain has been mapped at a scale of 1:100 000. The stratigraphy and structural history of BRS and DGC rocks and the petrogenetic evolution of BRS metavolcanic and DGC granitic rocks are documented in the present work. The BRS is sediment-dominated and is characterised by abundant argillites and quartz wackes, originally turbidites, and minor jasperoidal chemical sediments. The sediments separate four NNEtrending units composed of subaqueous tholeiitic basalts and consanguineous gabbroic intrusives locally, with andesites and extensive, proximal, subaerial andesitic volcaniclastic deposits. Major and trace element geochemical data suggest that the basalts are all very similar: They are depleted in Ti, P, 'h and Y and enriched in LILE relative to MORB and commonly have flat chondrite-normalised REB patterns of ca. x10 abundance. These mafic metavolcanics are geochemically comparable to modem immature, island arc and back-arc basin basalts. The geochemical and lithological characteristics of the andesitic rocks are typical of mature, calc-alkaline island arc assemblages. The south-western flank of the BRS is composed of coarse-grained, arkosic wackes with abundant polymict paraconglomerate horizons that contain clasts of rhyolite, granite, granitic gneiss and basalts. The siliciclastic sediments are fanglomerates and were originally deposited on a continental margin or in a small, embryoniC fore-arc basin from a highland region to the west These sediments are interbedded with a subaerial assemblage of calc-alkaline rhyolites and tholeiitic basaltic rocks. Geochemical similarities between the rhyolites and the DGC suggest a co-genetic relationship. The basalts interbedded with the fanglomerates are enriched in incompatible elements relative to basalts elsewhere in the BRS, suggesting contamination of the continental margin. Non-coaxial progressive bulk heterogeneous deformation (01) produced sinistral, strike-slip shear zones and resulted in upright, NNE-striking, commonly mylonitic fabrics, in all but the post-tectonic granitoids. Strain was partitioned into zones of progressive simple shear across which zones of progressive pure shear (flattening) developed. This major DI deformation occurred in response to oblique convergence of the BRS and DGC. A plate tectonic model is proposed for the evolution of the BRS and DGC of the Boundiali region. Immature arc-like rocks and marginal basin sediments became progressively accreted to a continental margin during oblique subduction and basin closure. The proposed model suggests that the basin developed by block faulting of a juvenile, "Dabakalian" (ca. 2.25 Ga) crust, although isotopic data is not available to distinguish between this model and one involving terrane accretion where no older basement is present Fresh dolerites cross-cut the BRS and DGC rocks. They are quartz- and olivine-normative tholeiites and were generated from a heterogeneous subcontinental lithospheric source. They are thought to be Mesozoic in age and related to widespread dolerites and basalts that mark continental fragmentation of the Gondwanaland supercontinent
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Geology Geology Mineralogy Sedimentology Geochemistry