May 2011 LIP of the Month

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Large igneous provinces of the West African Craton: The record preserved in regional dyke swarms.

Nasrrddine Youbi 1, 2 & 3 , Richard Ernst4,5, Ulf Söderlund 6, Hervé Bertrand 7 , Miguel Doblas 8 , Hind El Hachimi 1, Djiky Kouyaté 1 , Abderrahmane Soulaimani 1, Ahmid Hafid 9, Moha Ikenne 10, and Khalid Rkha Chaham 1

1 Dept of Geology, Faculty of Sciences-Semlalia, Cadi Ayyad University, Prince Moulay Abdellah Boulevard, P.O. Box 2390, Marrakech, Morocco, Email:

2 Centre National pour la Recherche Scientifique et Technique, Angle avenues des FAR et Allal El Fassi, Madinat Al Irfane B.P. 8027 Nations Unies, 10102 Rabat, Morocco ;

3 Centro de Geologia, Universidade de Lisboa (CeGUL), Faculdade de Ciências, Deparmento de Geologia, Lisboa, Portugal;

4 Ernst Geosciences, 43 Margrave Ave Ottawa, Ontario K1T 3Y2 Canada.

5 Department of Earth Sciences, Carleton University, Ottawa, Canada K1S 5B6. Email:

6 Lithosphere and Biosphere Sciences, Dept. of Earth and Ecosystem Sciences, Division of Geology, Lund University, Sölvegatan 12, S-223 62 Lund, Sweden, Email:;

7 Laboratoire Sciences de la Terre, ENS de Lyon et UCBL, 46, Allée d'Italie, 69364 Lyon, France. E mail :

8 Departamento de Geología, Museo Nacional de Ciencias Naturales, CSIC, José Gutiérrez Abascal 2, 28006 Madrid, Spain

9 Dept of Geology, Faculty of Sciences & Technics Guéliz, Cadi Ayyad University, P.O. Box 549, Abdelkarim El Khattabi Avenue, Guéliz, Marrakech, Morocco, Email:;

10 Dept of Geology, Faculty of Sciences, Ibnou Zohr University, P.O. Box 28/S, Agadir, Morocco, Email:


Regional dyke swarms are considered to represent periods of repeated crustal extension wherein enormous amounts of mantle-derived magmas ascend through the crust. Their distribution, palaeomagnetism, petrology, geochemistry and emplacement ages are of intense geodynamic interest since they provide invaluable clues to our understanding of the nature of the sub-continental lithospheric mantle. There is also an increasing global recognition of their utility in delineating the existence and extent of Large Igneous Provinces (LIPs) and, especially, to use their exact emplacement ages and dyke directions to reconstruct formerly adjacent crustal blocks (e.g., Bleeker and Ernst, 2006; Ernst and Bleeker, 2010). Thus, the study of dyke rocks is extremely important in order to reveal the configuration of ancient supercontinents.

In this contribution we present a preliminary survey of mafic dyke swarms of the West African craton (WAC). The synthesis demonstrates the complexity in the dyke record, suggesting that geochronological, petrological, geochemical and paleomagnetic characteristics of many dyke sets remain to be established before WAC and its shield areas can be put into a global plate tectonic framework (e.g., Youbi et al., 2010).

Geological setting of the West African Craton.

The WAC, stable since 2 Ga, constitutes the basement of northwestern Africa (e.g., Ennih and Liégeois, 2008). The WAC is composed of three Archean and Paleoproterozoic shields: the Reguibat Shield, the Anti-Atlas and the Leo-Man shield, separated by two cratonic sedimentary basins. The basement of the WAC was built through several major orogenic cycles: the Paleoarchean–Leonian cycle (multiple episodes between 3.5 and 3.0 Ga) related to continental accretion and volcano-sedimentary activity whose chronology remains uncertain (e.g., Thiéblemont et al., 2004), the Liberian cycle (2.95–2.75 Ga; Key et al., 2008), the Eburnian–Birimian cycle (2.2–1.75 Ga; Schofield et al., 2006) and the Pan-African orogenic event (760–660 Ma; Thomas et al., 2002). One of the main characteristics of the WAC is that no Mesoproterozoic events or rocks are known, suggesting a quiescent period between 1.7 and 1.0 Ga (e.g., Ennih and Liégeois, 2008). The exposed parts of the craton outcrop in two main uplifts: the Reguibat Shield in the north (Mauritania, Morocco and Algeria) and the Leo-Man Shield in the south, and in smaller inliers of the Anti-Atlas belt.

Figure 1: General geology of the West African craton (Fabre, 2005; Liégeois et al., 2005; Ennih and Liégeois, 2008).

Petrogrphical and geochemical data on mafic dyke swarms in the WAC

The dykes and sills of the WAC display remarkably uniform textural, mineralogical and geochemical features throughout the area in which they occur. They all consist essentially of tholeiitic basalts and are typically composed of plagioclase + clinopyroxene (augite) ± orthopyroxene (enstatite) ± olivine displaying doleritic texture and variable grain size. From the geochemical point of view, they are all characterized by a clear negative Nb anomaly, indicating a plausible subduction fingerprint and/or crustal contamination (e.g., Bassot et al., 1986; Ikenne et al., 1997; Hafid et al., 2001; Verati et al., 2005 Deckart et al., 2005; Chabou et al., 2010; Cournède, 2010). The similarities of all their trace element patterns play in favor of a single geodynamic environment or a common influence of contamination from sub-lithospheric mantle. These conditions should have been consistent for a long period of time, according to the large range of available ages.

Figure 2: Primitive mantle-normalized trace element 'spidergrams' of selected dyke swarms from the West African craton (a) CAMP dyke swarms of Mali, Algeria, and Guinea (Deckart et al., 2005; Verati et al., 2005; Chabou et al., 2010). Symbols: open triangle, Intermediate-Ti group dykes of Taoudenni basin, Mali; filled triangle, Low-Ti group dykes of Taoudenni basin, Mali ; open square, Low-Ti group of dolerite of Reggane basin ; filled square, Low-Ti group of dolerite of Hank basin; open diamond, Low-Ti group of dolerite of Fersiga; filled diamond, Great Ksi-Ksou dyke; open circle, Fouta Djalon dolerite dykes, Guinea and (b) Precambrian dyke swarms of Burkina Faso (Cournède, 2010). Symbols: open triangle, Dolerite dykes trending NW-SE with an approximate age ranging from 2200 ± 370 Ma (Sm/Nd method) to 1631± 250 Ma (Rb/Sr method); filled triangle, Dolerites dykes trending NE-SW with an approximate age ranging from 847±360 Ma (Sm/Nd method) to 664±280 Ma (Rb/Sr method). Primitive mantle normalizing values are from Sun and McDonough (1989).

Geochronological data on mafic dyke swarms in the WAC

The compilation of geochronological data on mafic dyke swarms in the West African Craton is dominated by the identification of the so-called Central Atlantic Magmatic Province (CAMP), although it has become increasingly apparent that not all mafic dyke swarms fall into this category (Table 1).

The CAMP LIP was emplaced at ca. 200 Ma, close to the Triassic–Jurassic boundary (Marzoli et al., 1999), during the early stages of the break up of the supercontinent of Pangaea that led to the opening of the Central Atlantic Ocean. CAMP magmatism is nowadays represented by remnants of intrusive (crustal underplates, layered intrusions, sills, dykes) and extrusive (pyroclastic sequences and lava flows) rocks that occur in once-contiguous parts of northwestern Africa, southwestern Europe, and North and South America (e.g., McHone and Puffer, 2003; Youbi et al., 2003; Knight et al., 2004; Marzoli et al., 2004). It may have covered over 7 x 106 km2, with a total volume of magma estimated at 2–4×106 km3 and was active for no more than 4-5 Ma. 40Ar/39Ar plateau ages of CAMP range from 205 to 190 Ma, with a peak activity around 199 Ma on the African margin (e.g., Nomade et al., 2007). Preserved lava flows, common in Morocco and Portugal (e.g., Bertrand, 1991; Youbi et al., 2003; Martins et al., 2008), are rare in Algeria, North and South America, and have been dated between 203 and 190 Ma, again with peak activity at about 197-199 Ma (e.g., Chabou et al., 2007; Verati et al., 2007). Most of the CAMP rocks are tholeiitic low-Ti Continental Flood Basalts (CFBs), whereas high Ti CFBs are restricted to a narrow zone in the southern margin of the WAC (Liberia, Sierra Leone) and north-eastern South America (Surinam, French Guyana and northern Brazil) (e.g., Merle et al., 2011). However, the geographic boundaries of the CAMP remain uncertain, especially in Africa and South America. Recent investigation suggests that the CAMP was emplaced as far as the sub-Andean area in southern Bolivia, about 3000 km from the Atlantic margin (Bertrand et al., 2005) and indicates that the extension of the CAMP magmatism is probably much larger than previously recognized. The Central Atlantic LIP is considered as the result of a mantle super-plume (e.g., Oyarzun et al., 1997; Wilson, 1997) or, alternatively, as a consequence of lithosphere extension and thinning, pre-dating the Atlantic opening, that triggered decompressional melting in the upper asthenosphere (e.g., Withjack et al., 1998). Magmatism is apparently coeval with the mass extinction at the Triassic–Jurassic boundary (e.g., Van de Schootbrugge et al., 2009).

In addition to the mafic dyke and sill swarms that are linked to the CAMP LIP, a number of mafic units can be linked to the CIMP and the EUNWA LIP groups (each representing a clustering of related LIPs emplaced over a more extended time). The so-called Central Iapetus Magmatic Province (CIMP) was emplaced during Ediacaran-Cambrian times, and has been linked to the disruption of the supercontinent of Rodinia (Pannotia) leading to the initial opening of the Central Iapetus Ocean in the triple junction Laurentia, Baltica, and Amazonia or northwestern Africa (e.g., Ernst and Buchan, 1997; Puffer, 2002, Doblas et al., 2002, Coltice et al., 2007; Ernst and Bleeker; 2010; Ernst and Bell, 2010). As for the CAMP, the Central Iapetus LIP group has been variably considered as the result of a mantle super-plume (e.g., Puffer, 2002) or of heat incubation below the Rodinian (Pannotian) super-continent (e.g., Doblas et al., 2002; Coltice et al., 2007). Although major volcanic events are commonly associated with environmental hardship and even mass extinction (example CAMP versus Triassic-Jurassic mass extinction), the CIMP LIP group correlates with the beginning of a major expansion in the diversity and quantity of marine life during the early Cambrian: the Cambrian bio-radiation event (Puffer, 2002). It correlates also with the last Precambrian glaciation: the so called Gaskiers glaciation that occurred around 580 Ma. Major glaciations (e.g., Eyles, 2008), are associated to an extensional context and to LIPs. Volcanic activity may have enhanced the climate change (e.g., Stern et al., 2008). These authors develop and explore the hypothesis that explosive volcanism was at least partly responsible for Neoproterozoic climate change, synopsized as the “Volcanic Winter to Snowball Earth” (VW2SE) hypothesis. The CIMP magmatism is best studied along the Laurentian margin (Puffer 2002; Ernst and Buchan 2001, 2004; McCausland et al. 2007) and has main pulses at ca. 615 Ma, 590 Ma, 560 and 550 Ma, which are potentially linked with the progressive breakup of the eastern Laurentian margin (Kamo et al. 1989; Bingen et al. 1998; Waldron and van Staal 2001; Cawood et al. 2001; Ernst and Buchan 2004). It is also present in Baltica (e.g., Ernst and Bell, 2010 and references therein) where it is best expressed by the Ediacaran CFB from the southwestern margin of the East European Craton in Ukraine. Whole-rock 40Ar/39Ar age determination revealed plateau ages at 590–560 Ma (Elming et al., 2007). In Africa, the CIMP LIP group is well represented around the WAC (e.g., Doblas et al, 2002), in particular in the High and the Anti-Atlas of Morocco, where it occurs as dyke swarms (Ediacaran Assarag -Douar Eçour dyke Swarms) that represent the feeder dykes of the volcanic successions of the Ouarzazate Group (formerly “PIII” of Choubert, 1963). The Ouarzazate Group represents a volcano-sedimentary sequences highly variable in thickness consisting of coarse volcanic conglomerates, ignimbritic rhyolites, trachytes, andesites, basalts, tuffites, and rare interbedded stromatolitic layers and fault scarp breccias. Various types of intrusions, such as granitoid massifs, necks, dykes or ring dykes are emplaced within the early Ouarzazate Group and within underlying units. The Sidi El Houssein alkaline granite (579 ± 7 Ma) is a typical example of ring-complex intrusion within the Eburnian basement. Felsic volcanics from the Ouarzazate Group were dated in several inliers: between 575 and 560 Ma in the Sirwa Window which includes the Zenaga inlier (U–Pb SHRIMP on zircons, Thomas et al., 2002); 563 ± 5 Ma and 580 ± 12 Ma in the Central Anti-Atlas (U–Pb zircon; Mifdal and Peucat, 1985); 565 ± 7 Ma in the Tagragra de Tata inlier (U–Pb SHRIMP on zircons; Walsh et al., 2002); 550 ± 3 Ma in the Imiter inlier (U–Pb IMS 1270 on zircons; Cheilletz et al., 2002). The Ouarzazate Group has not recorded the Pan-African deformation, but was deposited on a highly variable basement topography, which, coupled with the large and rapid variations in thickness of the Ouarzazate Group itself, strongly suggests that this group was deposited during active tectonics, most probably associated with transtensional movements (Doblas et al., 2002; Gasquet et al., 2005, 2008).

The so-called European North West African Magmatic Province (EUNWA or EUNWAMP) (e.g., Doblas et al., 1998; see also Wilson et al., 2004) was emplaced during Carboniferous-Permian times, and has been linked to the gravitational collapse of the previously overthickened and weakened Hercynian (Variscan) orogenic belt (the initial stages of the disruption of the Pangaean supercontinent). The whole Variscan edifice collapsed through simple-pure shear low-angle extensional detachments during the late Variscan, giving rise to Basin and Range type extensional province in Europe, and northwestern Africa involving major low angle detachment faulting, unroofing of large metamorphic core complexes, and synextensional plutonic bodies, dyke and sill swarms and volcanic successions. Coevally with an extensional scenario, Europe, and northwestern Africa were affected by a complex system of conjugate strike slips faults (NE-SW sinistral and NE-SE dextral) which partially disrupted the Variscan edifice, resulting in new Permo-Carboniferous stress pattern with the principal compressional axis oriented N-S (Arthaud and Matte, 1975; 1977). This episode was accompanied by sediment deposition and volcanism in transtensional and pull-apart basins (Youbi et al., 1995; Doblas et al., 1998). This episode resulted from dextral transcurrent movement along an intracontinental zone located between Gondwana and Laurussia an early proposal of Van Hilten (1964) later reinterpreted by Arthaud and Matte (1975; 1977). To date a range of chronometers has been applied to determine eruption ages from across the region of the EUNWA LIP group including whole-rock Rb–Sr and K–Ar dating, 40Ar/39Ar dating of mineral separates and U–Pb dating of zircon, titanite and perovskite (e.g., Timmerman et al., 2009). The duration of activity is currently estimated to span a period of ca. 100 million years, from Early Carboniferous to Upper Permian-Early Triassic (350–250 Ma), with several hiatuses (Upton et al., 2004). Three main pulses can be distinguished at ca. 300 Ma, 290-275 Ma, and 250 Ma, and each of these pulses can be considered a separate LIP within the overall EUNWA LIP group. These eruptive cycles are well represented in Morocco in northwestern Africa and also in southern Scandinavia and northern Germany. The huge volume of extruded and intruded magmatic products of the EUNWA magmatic province (example in the Oslo Graben, the estimated volume is at ca. 35,000 km3 while in the North German Basin, the total volume of felsic volcanic rocks, mainly rhyolites and rhyodacites, was of the order of 48,000 km3) has led to suggestions of a thermally anomalous mantle plume to explain this pulse of the magmatism (Ernst and Buchan, 1997; Torsvik et al., 2008). A significant detractor from a plume hypothesis is the duration of activity and the helium isotope signature of lithospheric mantle xenoliths from the Scottish Permo-Carboniferous dykes, sills and vents (Kirstein et al., 2004). The EUNWA magmatic province may have contributed to the great Gondwanan glaciation that occurred from the Late Devonian to the Late Permian (Veevers and Powell, 1987; Crowell, 1999; Isbell et al., 2003). Glaciers achieved their maximum paleolatitudinal range between the middle Stephanian (ca. 305 Ma ago) and near the end of the Sakmarian (ca. 284 Ma ago) (Isbell et al., 2003). This hypothesis is termed the icehouse–silicic large igneous province (SLIP) hypothesis (Cather et al., 2009).

Country Location-Dyke/Sill complex or intrusions Age (Ma) Method Reference LIPs
Algeria Reguibat Shield Dyke Swarm 1900 ±  0.05 Pb-Pb (baddeleyite)  [1,2]   
Algeria Hoggar-Tin Serririne  Dyke Swarm 351.6 ±16.0-347.6 ± 16.2  K-Ar (whole-rock/plagioclase )  [3,4]  EUNWA ?
Algeria Ksi-Ksou Dyke 198.0 ± 1.8 Ar-Ar (plagioclase)  [5]  CAMP
Algeria Hank-Reggane- Fersiga  Sills & Dykes 197.9 ± 2.0 -195.0 ± 1.6  Ar-Ar (plagioclase)  [6]  CAMP
Algeria Reggane Sill 166 K-Ar (whole-rock )  [7]  CAMP
Algeria Hoggar-Tin Seririne 369 ± 9 K-Ar (whole-rock )  [8]  EUNWA ?
Burkina Faso Central Burkina Faso 250 ± 13    [9,10]  EUNWA ?
Burkina Faso Central Burkina Faso 1814  ±  26    [9]   
Burkina Faso Dolerites dykes trending NW-SE 2200 ± 370 Ma  Sm-Nd (whole-rock) [11]   
Burkina Faso Dolerites dykes trending NW-SE 1631± 250 Ma  Rb-Sr (whole-rock) [11]   
Burkina Faso Dolerites dykes trending NE-SW  847±360  Sm-Nd (whole-rock) [11]   
Burkina Faso Dolerites dykes trending NE-SW  664±280 Ma  Rb-Sr (whole-rock) [11]   
Guinea Kakoulima-Fouta Djalon  Dyke Swarm  200.4 ±  0.2- 194.8 ±  0.5  Ar-Ar (biotite) [12,13]  CAMP
Guinea Bafata-Burquelem Dyke Swarm 197 ± 7- 153 ±  3 Ma K-Ar (whole-rock )  [14]  CAMP
Liberia Liberia Dyke Swarm 197  ± 6-177  ± 4  K-Ar ( plagioclase, pyroxene, whole-rock )  [15]  CAMP
Liberia Liberia Dyke Swarm 186 ± 4 Ma - 201± 2 K-Ar (whole-rock )  [16]  CAMP
Liberia Liberia Dyke Swarm 196 ± 4 Ma - 177 ± 4 K-Ar (plagioclase, whole-rock)  [17,18]  CAMP
Liberia Liberia Dyke Swarm 185.0 ± 4.4- 187.0 ±  3.4 Ar-Ar (plagioclase)  [15]  CAMP
Mali Gourma 275 ± 14-260 ± 13 K-Ar (whole-rock )  [19]  EUNWA ?
Mali Banfora 250 ± 13 K-Ar (whole-rock )  [19]  EUNWA ?
Mali Taoudenni  Dyke Swarm 203.7 ± 2.7-200.9 ± 2.5 Ar-Ar (plagioclase)  [5]  CAMP
Mali Taoudenni  Dyke Swarm 200.0 ± 0.7 -197.6 ± 0.8  Ar-Ar (plagioclase)  [20]  CAMP
Mali Taoudenni Dyke Swarm 199.8  ±  2.6-196.6 ± 1.0 Ar-Ar (plagioclase)  [20]  CAMP
Mali Taoudenni Sills Drilling ONU 202.4  ±  1.6-198.9  ±  1.2 Ar-Ar (plagioclase)  [20]  CAMP
Mauritania Reguibat Shield Dyke Swarm 1757-815  K-Ar (whole-rock )  [21]   
Mauritania Reguibat Shield Dyke Swarm 1609 ± 45 Rb-Sr (whole-rock )  [22]   
Mauritania Taoudenni Adrar Sill 308.9 ± 1.1 - 233 ± 1 Ar-Ar (plagioclase)  [22] EUNWA ?
Mauritanie Ballé 230 ± 11 K-Ar (whole-rock )  [19] EUNWA ?
Mauritanie Taoudenni  265 ± 13 K-Ar (whole-rock )  [19] EUNWA ?
Mauritanie Hodh & Akjoujt Dyke Swarm 201-172 K-Ar (whole-rock )  [23] CAMP
Mauritanie Hank Dyke Swarm 206-147/1507-1429/307-223 K-Ar (whole-rock )  [23] CAMP
Mauritania Amsaga -Reguibat Shield Dyke Swarm 2706  ±  54 Ma Sm-Nd (plagioclase, pyroxene, whole-rock) [24]  
Morocco Anti-Atlas-Tagragra of Tata Dyke Swarm 2040 ±  6  SHRIMP U-Pb (zircon)  [25]  
Morocco Anti-Atlas-Zenaga  Dyke Swarm 2039.7  ±  2.1 U-Pb (zircon) [26,27]  
Morocco High-Atlas-Douar Eçour Dyke Swarm 579 ± 7 -  559 ± 6  SHRIMP U-Pb (zircon)  [28] CIMP
Morocco Anti-Atlas-Assarag  Dyke Swarm 579 ± 7 - 559 ± 6  SHRIMP U-Pb (zircon)  [28] CIMP
Morocco Anti-Atlas-Agnou Mghar Dyke 317 ± 7 - 236 ± 40 K-Ar (whole-rock )  [29] EUNWA ?
Morocco Anti-Atlas-Ighrem-Asdrem Dyke 210 ± 10 -174 ±  5 K-Ar (whole-rock )  [29] CAMP
Morocco Foum Zguid Dyke 187 ±  4 -182 ±  4 K-Ar (whole-rock )  [30] CAMP
Morocco Foum Zguid Dyke 168 ±  5 -152 ±  5 / 235 ± 10 K-Ar (whole-rock )  [31] CAMP
Morocco Foum Zguid Dyke 196.9 ± 1.8 Ar-Ar (plagioclase)  [5] CAMP
Morocco Draa Valley Sills 186 ±  3 -180 ±  4 K-Ar (whole-rock )  [30] CAMP
Nigeria Oban-Obudu Dyke Swarm 219.9 ±  4.7-204.0 ± 9.9  K-Ar ( plagioclase)  [32] CAMP
Nigeria Oban-Obudu Dyke Swarm 140.5 ±  0.7 Ar-Ar ( plagioclase)  [33] CAMP ?
Niger Bossé Bangou 1011 ± 45.7 K-Ar (whole-rock )  [34]  
Niger Libiri (Bolsi-Bossé Bangou) 1377.6 ± 35.5 K-Ar (whole-rock )  [34]  
Niger Bilabé 1379.5 ± 26.9 K-Ar (whole-rock )  [34]  
Niger Gabou (Tilabéri) 896 ± 24.5 K-Ar (whole-rock )  [34]  
Senegal Sambarabougou-Kondhoko Dyke Swarm 1339 ± 37- 1124 ±  24 K-Ar (whole-rock )  [14]  
Senegal Etiolo Dyke Swarm 463 ±  13 K-Ar (whole-rock )  [14]  
Senegal N'Débou Dyke Swarm 325 ± 17- 311 ±  14/170 ±  5 K-Ar (whole-rock )  [14] EUNWA ?
Sierra Leone Freetown Complex 194 ±  8-165 ± 10 K-Ar (whole-rock )  [35] CAMP
Sierra Leone Freetown Complex 196.3 ±  3 -232.1 ±  9 Ar-Ar (amphibole, biotite, plagioclase)  [36,37] CAMP

Notes for Table 1: Geochronological data on mafic dyke swarms in the West African Craton. [1] Aïfa et al., (2001); [2] Lefort and Aïfa (2001) ; [3] Djellit et al., (2006); [4] Derder et al., (2006); [5] Sebai et al. (1991); [6] Chabou et al. (2007); [7] Conrad et al., (1972); [8] Bayou et al., (2004); [9] Castaing et al. (2003); [10] Marcelin and Serre (1971); [11] Cournède (2010); [12] Deckart et al. (1997); [13] Nomade et al. (2007); [14] Bassot et al. (1986); [15] Dalrymple et al. (1975); [16] Mauche et al. (1989); [17] Lanphere and Dalrymple (1971); [18] Lanphere and Dalrymple (1976); [19] Lay and Reichelt 1971); [20] Verati et al. (2005); [21] Dosso et al. (1979); [22] Rooney et al. (2010); [23] Dosso (1975); [24] Potrel et al. (1998); [25] Walsh et al. (2002); [26] Kouyaté et al. (2010a); [27] Kouyaté et al. (2010b); [28] Thomas et al. (2002); [29] Huch,(1988); [30] Hailwood and Mitchell (1971); [31] Leblanc (1973); [32] Ekwueme et al. (1997); [33] Ekwueme (1994); [34] Ama Salah (1991);[35] Briden et al. (1971); [36] Barrie et al. (2006); [37] Barrie et al. 2010). CAMP = the Late Triassic-Early Jurassic Central Atlantic Magmatic Province; CIMP = the Late Neoproterozoic Central Iapetus Magmatic Province; EUNWA = the Permo- Carboniferous European North-West African Magmatic Province.

Economic potential of mafic dyke swarms in the WAC

Few minerals of economic importance are associated with minor basic intrusions, and the dykes and sills dolerites of the WAC are no exception to this rule. There is always the possibility of contact metasomatism or hydrothermal mineralization, but the titanium-rich magnetite and copper findings near Nioro in the southern Taoudenni basin (where dolerite intrudes limestone), are almost certainly of curiosity value only. Limited amounts of iron have formed by lateritic alteration of a thicker sill in Guinea. There are Ti-rich magnetite deposits in the Freetown Complex (of the CAMP event), and sulphides of copper as well as nickel associated with platinum and gold. However, the grades are very low and the total amount involved is probably rather low since the intrusion itself is of relatively small size. The main use of dolerites is as crushed rock for construction work and rail ballast.


This work is a contribution to the following research projects: (i) International Collaborative Research Grant, Swedish-MENA Research Links Programme to Ulf Söderlund, and Nasrrddine Youbi, which is funded by the Swedish Research Council (SRC) and the Swedish International Development Cooperation Agency (SIDA); (ii) International Government-Industrial-Academic Programme “Reconstruction of Supercontinents Back To 2.7 Ga Using The Large Igneous Province (LIP) Record, With Implications For Mineral Deposit Targeting, Hydrocarbon Resource Exploration, and Earth System Evolution” (see the URL for more details) and (iii) PICS, CNRS (France) - CNRST (Morocco) to Hervé Bertrand and Nasrrddine Youbi.


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