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

2001 ◽  
Vol 112 (3-4) ◽  
pp. 289-302 ◽  
Author(s):  
Nasser Ennih ◽  
Jean-Paul Liégeois
Keyword(s):  
West African ◽  
Passive Margin ◽  
Northern Limit ◽  
The West ◽  
West African Craton ◽  
Pan African

Where are the Eburnian–Transamazonian collisional belts?

1990 ◽  
Vol 27 (10) ◽  
pp. 1382-1393 ◽  
Author(s):  
Jean Michel Bertrand ◽  
Emmanuel Ferraz Jardim de Sá
Keyword(s):  
West African ◽  
High Grade ◽  
The West ◽  
West African Craton ◽  
Early Proterozoic ◽  
Late Proterozoic ◽  
Nappe Tectonics ◽  
Pan African ◽  
Orogenic Belts ◽  
Lower Crustal

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.

The Equatorial Atlantic Laboratory: sediment routing systems and lithosphere deformation

2020 ◽  
Author(s):  
Delphine Rouby ◽  
Dominique Chardon ◽  
Jing Ye ◽  
Flora Bajolet ◽  
Artiom Loparev ◽  
...  
Keyword(s):  
West African ◽  
Passive Margin ◽  
Rift System ◽  
Equatorial Atlantic ◽  
The West ◽  
Geological Time Scale ◽  
West African Craton ◽  
Continental Scale ◽  
Sediment Routing ◽  
Atlantic Margin

<p>We summarize the results of a 7 years study of the sediment routing systems of the West African Craton transporting its erosional products to the Central and Equatorial Atlantic passive margins at geological time scale. We used paleogeograhic maps to define the geodynamics framework of this routing system with in particular the propagation of the Equatorial Atlantic oblique rift separating the West African and Amazonian Cratons. We used sub-surface data to evaluate the evolution of lithosphere necking distribution along the conjugated African and South American margins of the rift system. We estimated the long-term denudation pattern at continental scale from low temperature thermochronology measures of samples from 3 transects perpendicular to the Atlantic margin. We used the exceptional preservation of geomorphologic markers to reconstruct the drainage system of the craton since 45 Ma, and estimate the associated denudation and exports of terrigeneous sediments to the Atlantic margin. Finally, we estimated the accumulation history in the passive margin basins and compare them with the estimated denudation histories from thermal histories and geomorphologic markers. We show that the modes of preservation of sedimentary export in the passive margin basins are highly variable in time (immediate post roft versus late post-rift) and space (transform/oblique versus divergent margin segments). We show that the present day drainage of the West African Craton as been stable since 30 Ma when it underwent a major reorganization driven by the growth of the relief associated with the Hoggar mantle plume. We show that accumulation in the passive margin basins fall within the same order of magnitude than denudation on the craton at the scale of the Meso-Cenozoic. This allows us to argue to the relevance of using the stratigraphic architecture of passive margin basins to estimate the denudation history of their continental domains.</p>

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)

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.

Detrital zircon sources in the Ordovician metasedimentary rocks of the Moroccan Meseta: Inferences for northern Gondwanan passive-margin paleogeography

2022 ◽  
Author(s):  
Cristina Accotto ◽  
David Martínez Poyatos ◽  
Antonio Azor ◽  
Cristina Talavera ◽  
Noreen Joyce Evans ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
West African ◽  
Passive Margin ◽  
Variscan Orogeny ◽  
The West ◽  
West African Craton ◽  
Metasedimentary Rocks ◽  
Population Peak ◽  
A Minor ◽  
Detrital Zircon Ages

ABSTRACT Detrital zircon U-Pb geochronology has been widely used to constrain the pre-Carboniferous geography of the European and, to a lesser extent, the Moroccan Variscides. The latter have been generally considered as part of a long-lasting passive margin that characterized northern Gondwana from Ordovician to Devonian time, and was subsequently involved in the late Paleozoic Variscan orogeny. We report detrital zircon ages for three Early to Late Ordovician samples from the Beni Mellala inlier in the northeastern part of the Western Moroccan Meseta in order to discuss the temporal evolution of the sources of sediments in this region. The detrital zircon spectra of these samples, characterized by two main populations with mean ages of 630–610 Ma and 2170–2060 Ma, are typical of Cambrian–Devonian rocks from the Moroccan Variscides and confirm their link to the West African craton. A minor Stenian–Tonian population (peak at ca. 970 Ma) suggests the influence of a distant and intermittent NE African source (Sahara metacraton), which was probably interrupted after Ordovician time. Our data support previous interpretations of the Moroccan Meseta (and the entire northern Moroccan Variscides) as part of the northern Gondwana passive margin. The main sources of these sediments would have been the West African craton in the western regions of the passive margin (Moroc- can Meseta and central European Paleozoic massifs), and the Arabian-Nubian Shield and/or Sahara metacraton in the eastern areas (Libya, Egypt, Jordan, central and NW Iberian zones during Paleozoic time), where the 1.0 Ga detrital zircon population is persistent throughout the Ordovician–Devonian time span.

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

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.

Sign in / Sign up

Export Citation Format

Share Document