IGCP-485 Meeting and Field Excursion - Cratons, Metacratons and Mobile Belts: Keys from the West African Craton Boundaries Eburnian Versus Pan-African Signature, Magmatic, Tectonic and Metallogenic Implications

The reconstruction of Early Proterozoic crustal evolution and geodynamic environments, in Africa and South America, is incomplete if cratonic areas alone are studied. If the presence of high-grade gneisses is considered as a first clue to past collisional behaviour, 2 Ga high-grade gneisses are more abundant within the Pan-African–Brasiliano mobile belts than in the intervening pre-Late Proterozoic cratons. The West African craton and the Guiana–Amazonia craton consist of relatively small Archaean nuclei and widespread low- to medium-grade volcanic and volcanoclastic formations intruded by Early Proterozoic granites. By contrast, 2 Ga granulitic assemblages and (or) nappes and syntectonic granites are known in several areas within the Pan-African–Brasiliano belts of Hoggar–Iforas–Air, Nigeria, Cameroon, and northeast Brazil. Nappe tectonics have been also described in the Congo–Chaillu craton, and Early Proterozoic reworking of older granulites may have occurred in the São Francisco craton. The location of the Pan-African–Brasiliano orogenic belts is probably controlled by preexisting major structures inherited from the Early Proterozoic. High-grade, lower crustal assemblages 2 Ga old have been uplifted or overthrust and now form polycyclic domains in these younger orogenic belts, though rarely in the cratons themselves. The Congo–Chaillu and perhaps the São Francisco craton are exceptional in showing controversial evidence of collisional Eburnian–Transamazonian assemblages undisturbed during Late Proterozoic time.

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The Moroccan Anti-Atlas: the West African craton passive margin with limited Pan-African activity. Implications for the northern limit of the craton

Precambrian Research ◽

10.1016/s0301-9268(02)00169-9 ◽

2003 ◽

Vol 120 (1-2) ◽

pp. 179-183 ◽

Cited By ~ 15

Author(s):

El Hafid Bouougri

Keyword(s):

West African ◽

Passive Margin ◽

Northern Limit ◽

The West ◽

West African Craton ◽

Pan African

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Reply to discussion on “From Pan-African transpression to Cadomian transtension at the West African margin: New U-Pb zircon ages from the Eastern Saghro Inlier (Anti-Atlas, Morocco)” by Ikenne et al. 2020 (GSL-SP, 503, 209-233)

Journal of the Geological Society ◽

10.1144/jgs2021-034 ◽

2021 ◽

pp. jgs2021-034

Author(s):

Ezzoura Errami ◽

Ulf Linnemann ◽

Jamal El Kabouri ◽

Mandy Hofmann ◽

Andreas Gärtner ◽

...

Keyword(s):

West African ◽

Ultramafic Rocks ◽

Geodynamic Evolution ◽

The West ◽

West African Craton ◽

Zircon Age ◽

Pan African ◽

Stratigraphic Position ◽

Age Constraints ◽

Early Neoproterozoic

The comment of Ikenne et al. concerns recently described U-Pb baddeleyite ages, around 1.71 and 1.65 Ga, obtained on intrusive sills and dykes in the Taghdout-Lkest Group in the SW domain of the Anti-Atlas (AA). These authors suggest an independent geodynamic evolution of the eastern and western domains of the Anti-Atlas prior to the Ediacaran period. Furthermore, they state that we do not take this magmatic event into account when interpreting our data. We like to emphasize that this is beyond the scope of our paper and does not affect our interpretation of the AA evolution during the deposition of the Ediacaran sedimentary successions (Saghro, Mgouna, and Ouarzazate goups). We agree with the comment that we did not distinguish the Taghdout-Lkest from the Bleida-Tachdamt groups and now we separate them in the revised figure 2. The different geodynamic evolution of the SW and NE Anti-Atlas domains in pre-Ediacaran times sensu Ikenne et al., is not consistent with abundant inherited Paleoproterozoic zircon detritus and Nd model ages (0.80-1.82 Ga) from the northeastern Anti-Atlas and the Meseta. There is no doubt about Late Paleoproterozoic baddeleyite ages, but they do not have an analogue in the zircon age record of the West African Craton, which is expected from ultramafic rocks with few zircon grains. However, they locally allow assuming a Late Paleoproterozoic deposition of the lower Taghdout-Lkest Group. Any age constraints for the upper parts of this group are lacking, thus allowing a hypothetic deposition between ca. 1.65 Ga and 0.83 Ga (the assumed age of initial Bleida-Tachdamt Group deposition). Therefore, it is very important to close the gap in detailed stratigraphic studies that would allow differentiating between the different Late Paleoproterozoic and Early Neoproterozoic events including the stratigraphic position of the upper Taghdout-Lkest Group and Bleida-Tachdamt group.

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The Moroccan Anti-Atlas: the West African craton passive margin with limited Pan-African activity. Implications for the northern limit of the craton

Precambrian Research ◽

10.1016/s0301-9268(01)00195-4 ◽

2001 ◽

Vol 112 (3-4) ◽

pp. 289-302 ◽

Cited By ~ 135

Author(s):

Nasser Ennih ◽

Jean-Paul Liégeois

Keyword(s):

West African ◽

Passive Margin ◽

Northern Limit ◽

The West ◽

West African Craton ◽

Pan African

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Geodynamic context of the Proterozoïc deposits of the Firgoun Region (eastern border of the West African Craton, West Niger)

Geological Society London Special Publications ◽

10.1144/sp502-2019-115 ◽

2020 ◽

pp. SP502-2019-115

Author(s):

Diafarou Alzouma Amadou ◽

Moussa Konaté ◽

Yacouba Ahmed

Keyword(s):

Satellite Image ◽

West African ◽

Coarse Grained ◽

Compressive Deformation ◽

Normal Faults ◽

Reverse Fault ◽

The West ◽

West African Craton ◽

Deformation Stage ◽

Pan African

AbstractIn the Firgoun region located on the southwestern part of Niger, Proterozoic sedimentary deposits mark the southeastern edge of the West African Craton. The lowermost coarse-grained sandstones, structureless, are related to fluviatile deposits. They evolve vertically to alternating quartzitic sandstone beds and silty–clayey sandstone layers, interpreted as a shallow marine turbiditic sequence. The uppermost deposits have glacial features comparable with those found in Gourma and Taoudenni basins. These are diamictites interbeddeds–carbonates–silexites and cryoturbation features in slates, attributed to the association of ‘tillite–limestone–chert’ related to the ‘triad’. The Firgoun area deposits, as with their equivalents of Gourma and Béli basins, have recorded the Pan-African deformation episodes. In this paper we show that the studied deposits were firstly affected by an early distensive phase D1 and secondly by two Pan-African compressive episodes D2a and D2b. The distensive deformation episode is well recorded in the basal deposits (‘Sandstone of Firgoun Formation’). The deformation structures correspond to 70–80° N trending, syn-depositional normal faults. The plotting of the faults planes onto the stereographic diagram shows the prevailing of the extensional regime marked by a 140° N trending stretching. The first compressive deformation stage D2a is characterized in the basal deposits by isopachous folds and by anisopachous folds in the uppermost deposits. The combination of the satellite image and the plotting of the fold axial planes (30° N–45° NE to 50° N–50° NE) onto the stereographic diagram indicate a compressive regime with 120–140° N trending shortening. The last compressive deformation stage D2b is marked by thrust and reverse fault planes oriented 60–80° N, crosscutting all of the previous structures, mainly observed in the uppermost deposits (‘Béli–Garous Formation’). Their plotting onto the stereographic diagram reveals a 40° N shortening direction.

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Pan-African Paleostresses and Reactivation of the Eburnean Basement Complex in Southeast Ghana (West Africa)

Journal of Geological Research ◽

10.1155/2012/938927 ◽

2012 ◽

Vol 2012 ◽

pp. 1-15 ◽

Cited By ~ 9

Author(s):

Mahaman Sani Tairou ◽

Pascal Affaton ◽

Solomon Anum ◽

Thomas Jules Fleury

Keyword(s):

West African ◽

Normal Faulting ◽

Clockwise Rotation ◽

The West ◽

West African Craton ◽

Benue Trough ◽

Pan African ◽

Volta Basin ◽

Central Atlantic ◽

Eastern Edge

This faulting tectonics analysis concerns the southernmost segment of the Dahomeyide Orogen and the West-African craton eastern margin in southeast Ghana. The analysis of strike-slip faults in the frontal units of the Dahomeyide Belt indicates that four distinct compressive events (NE-SW, ENE-WSW to E-W, ESE-WNW to SE-NW and SE-NW to SSE-NNW) originated the juxtaposition of the Pan-African Mobile Zone and the West-African craton. These paleostress systems define a clockwise rotation of the compressional axis during the structuring of the Dahomeyide Orogen (650–550 Ma). The SE-NW and SSE-NNW to N-S compressional axes in the cratonic domain and its cover (Volta Basin) suggest that the reactivation of the eastern edge of the West African craton is coeval with the last stages of the Pan-African tectogenesis in southeast Ghana. An extensional episode expressed as late normal faulting is also recorded in this study. This E-W to SE-NW extension, which is particular to the southernmost part of the Dahomeyide Belt, appears to be post-Pan-African. This extension probably contributed to the formation of a major Jurassic rifting zone that originated the Central Atlantic and the Benue Trough.

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