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Interpretative bloc diagram of the Guelb el Azib complex. The letters refer to field photographs in Fig. 4. The location of the cross section is shown in Fig. 2.
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The Archean Guelb el Azib layered complex (GAC) in the West African craton of Mauritania is composed of an association of serpentinites, chromitites, amphibolites and anorthosites with few fine-grained amphibolite dykes. The complex forms tectonic slices in 2.9-3.5 Ga TTG gneiss terrains in close association with supracrustal rocks (BIFs, impure ma...
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... only gently dipping away from the major shear zone. Late dex- tral strike-slip movements are evidenced by horizontal lineations and asymmetric mantled porphyroclasts in shear zones of several tens of kilometres length. This last ductile event is also attested by upright folds with vertical axis that are well expressed in the surrounding BIFs (Fig. ...
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... highly tectonized, layered body affected by high-and low-grade metamorphism. Its original igneous stratigraphy can therefore not be reconstructed. The geometries of boundaries between the different lithological units presented on the geological map ( Fig. 2) are simplified; they more closely correspond to those drawn on the block diagram of Fig. ...
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... crop out as lenses of several metres width and tens of metre length (Fig. 3). They often occur within serpentinites and metawebsterites. Chromitites are either massive, brecciated (Fig. 4b) or disseminated within the host cumulates. Some lay- ered chromite pods have also been observed within anorthosite and leuco-amphibolite layers ( Fig. 4c and sample MA 435), a com- mon feature of Archean ...
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... Spinel veins (Fig. 4d) and rodingitic dykes (hydrogrossular-prehnite-chlorite rocks) cut across the ser- pentinites. Talc is often present either as small patches or as individualized spinel-talc rocks. Elliptical bodies of metaweb- sterite, hornblendite, amphibolite, anorthosite and chromitite are scattered within the main mass of serpentinite (Fig. ...
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... ultramafic cumulates consist of partly serpen- tinized metawebsterites, metatroctolites, hornblendite and mela-amphibolite, with some lenses of chromitites. Elliptical bodies of mafic material and serpentinite are also commonly found (Fig. 3). Despite strong deformation and pervasive metamorphism, igneous layering is preserved in both mela-amphibolites (Fig. 4e), ultramafic cumulates and a few chromitites. Anorthosites, leuco-amphibolites and meso-amphibolites form a distinct unit despite the presence of a few bodies of serpentinite. Igneous layering can still be found ...
Citations
... Early terrestrial anorthosites form part of layered intrusions that consist inter alia of leucogabbros, gabbros, melanogabbros, gabbronorites, websterites, bronzitites, hornblendites, peridotites, harzburgites, dunites, lherzolites, and chromitites (Ashwal, 1993(Ashwal, , 2010Ashwal and Myers, 1994;Windley and Garde, 2009;Ashwal and Bybee, 2017;Polat et al., 2018a;Polat, 2020, 2023;Sotiriou et al., 2024). These layered intrusions occur on every continent and range in age from 3950 Ma to 2500 Ma ( Fig. 1; Supplementary Data Tables S1 and S2; Subramaniam, 1956;Windley et al., 1973;Williams, 1988Williams, , 1989Ashwal, 1993;Balashov et al., 1993;Paixão, and Oliveira, 1998;Tenczer et al., 2006;Zeh et al., 2010;Berger et al., 2013;Santosh and Li, 2018;Polat, 2020, 2023;Anoop et al., 2022;Sotiriou et al., 2024). The mapped/inferred sizes of these intrusions vary from < 1 km 2 to 560 km 2 , attaining thicknesses of up to 7 km (Fig. 3;Ashwal, 1993;Polat et al., 2018a;Polat, 2020, 2023;Sotiriou et al., 2024). ...
In a paper in 1970, Brian Windley first recognised that early terrestrial and lunar anorthosites both have calcic plagioclase, and low TiO2 and high CaO and Al2O3 contents. Despite these similarities, the geochemistry of early terrestrial and lunar anorthosites has not been rigorously compared and contrasted. To this end, we compiled 425 analyses from 212 early terrestrial anorthosite occurrences and 306 analyses from 16 lunar anorthosite occurrences. This was supplemented by a compilation of plagioclase anorthite (An) contents and pyroxene Mg# from early terrestrial and lunar anorthosites. Early terrestrial anorthosites have lower whole-rock An contents but similar Mg# to lunar anorthosites. The CaO contents of lunar anorthosites are higher than those of early terrestrial anorthosites for a given MgO and Al2O3 content, early terrestrial anorthosites have higher SiO2 contents than lunar anorthosites at a given MgO content, and lunar anorthosites have higher Eu/Eu* anomaly ratios yet broadly similar La/Yb and Nd/Sm ratios than early terrestrial anorthosites. Some early terrestrial anorthosites have less fractionated chondrite normalised rare earth element (REE) patterns and less prominent positive Eu anomalies than lunar anorthosites. Lunar anorthosites have higher plagioclase An contents, yet a similar range of pyroxene Mg# compared to their early terrestrial counterparts. Some early terrestrial anorthosites are more fractionated than some lunar anorthosites. Our interpretations imply that most early terrestrial anorthosites crystallised from basaltic parental magmas that were generated by high-degree partial melting of sub-arc asthenosphere mantle wedge sources that were hydrated by slab-derived fluids, with the remainder being associated with mid-ocean and mantle plume settings. Some of the arc-related early terrestrial anorthosites were influenced by crustal contamination. In addition, early terrestrial anorthosites originated from partial melting of the mantle at various depths with variable garnet residua, whereas lunar anorthosites formed without any significant garnet residua. Lower plagioclase CaO contents and pyroxene Mg# in early terrestrial anorthosites can be explained by higher proportions of clinopyroxene and olivine fractionation in terrestrial magma chambers than in the lunar magma ocean where orthopyroxene and olivine fractionation occurred. Low TiO2 contents in both terrestrial and lunar anorthosites reflect rutile and/or ilmenite fractionation.
... Layered mafic to ultramafic rocks in Archean medium to high grade (amphibolite-facies to granulite-facies) metamorphic terranes commonly occur as fragmented units in spatial association with supracrustal rocks in granitoid gneiss (Windley et al., 1981;Sills et al., 1982;Hatcher et al., 1984;Polat et al., 2009;Hoffmann et al., 2012;Berger et al., 2013;Mohan et al., 2013;Bagas et al., 2016;Rajesh et al., 2020;Spier et al., 2022). Amphibole is a prominent mineral in mafic rocks of Archean layered complexes (Polat et al., 2009;Hoffmann et al., 2012;Huang et al., 2014;Sotiriou et al., 2020). ...
... It is important to keep in mind that in spite of the overprint events in Archean medium to high grade metamorphic terranes, the layered mafic-ultramafic rocks often preserve primary magmatic features. These include magmatic layering at various scales, cumulate textures and minerals of magmatic origin in an equant or inequigranular granoblastic-polygonal textured framework (e.g., Polat et al., 2009;Hoffmann et al., 2012;Berger et al., 2013;Bagas et al., 2016;Rajesh et al., 2020;Spier et al., 2022). In the case of amphibole, regardless of its occurrence as intercumulus phase, and as inclusions within pyroxenes, plagioclase and chromite (e.g., Polat et al., 2009Polat et al., , 2012Rollinson et al., 2010;Hoffmann et al., 2012;Huang et al., 2014;Sotiriou et al., 2020), there is the possibility of effect by metamorphic re-equilibration and/or metasomatic alteration. ...
... Over that time period significant juvenile crustal extraction has globally been documented throughout the world including the Guyana Shield (da Rosa-Costa et al., 2006;Delor et al., 2003;Gruau et al., 1985;Klein and Rodrigues, 2021;Lafon, 2019, 2020;Vanderhaeghe et al., 1998) and the West African Craton (Abouchami et al., 1990;Block et al., 2016;Eglinger et al., 2017;Grenholm et al., 2019;Parra-Avila et al., 2016Petersson et al., 2016Petersson et al., , 2018. In the West African Craton, the Archean and Paleoproterozoic shields crop out beneath the vast Neoproterozoic-Paleozoic Taoudeni basin as the Reguibat Shield in the north, the Leo-Man Shield in the south (Berger et al., 2013;Jessell et al., 2015;Potrel et al., 1996;Rocci, 1965;Thiéblemont, 2016) and the Paleoproterozoic Kayes and Kedougou-Kénieba Inliers between the two shields (Gärtner et al., 2017;Fig. 1). ...
Crustal evolution in the south West African Craton is dominated by a significant input of juvenile material into the crust at ca. 2.1 Ga and it remains unclear how much of the Paleoproterozoic continental mass was influenced by the presence of pre-existing Archean crustal domains. The Sassandra-Cavally (SASCA, Côte d'Ivoire) domain is strategically located east of the Sassandra shear zone at the transition of the Paleoproterozoic and Archean terranes of the Leo-Man shield. Combined U-Pb and Lu-Hf isotopic analyses by LA-(MC-)ICP-MS were acquired on zircon grains extracted from migmatitic gneisses, metasedimentary rocks and a granitic intrusion.
The migmatitic gneisses, yield Archean ages between ca. 3330 and 2810 Ma with εHf ranging from −9.4 to + 3.3 and a metamorphic age at 2076 ± 6 Ma. They are tentatively interpreted as orthogneisses extracted from the mantle during the Paleoarchean and reworked substantially in the Mesoarchean. Detrital zircon grains from metasedimentary units adjacent to the Archean migmatitic gneisses yield ages ranging from ca. 2213 to 2088 Ma with εHf ranging from + 0.0 to + 5.5, indicating derivation from juvenile Paleoproterozoic source rocks. A granite intrusion was dated within uncertainty of the metamorphic age at 2084 ± 6 Ma. It exhibits a hybrid isotopic signature with εHf forming two distinct clusters between −4.9 and −8.5, and between + 2.2 and + 6.5 for inherited zircon grains dated between ca. 2343 to 2100 Ma.
The near continuous U-Pb age record from this early Mesoarchean event to the Neoarchean is associated with constant initial ¹⁷⁶Hf/¹⁷⁷Hf suggesting for an ancient lead loss event at ca. 2800 Ma or a prolonged period of zircon dissolution/precipitation and/or crystallization. This early period is followed by peaks of zircon dates highlighting crustal extraction during the Eoeburnean (ca. 2250 to 2150 Ma) and Eburnean orogenies (ca. 2140 to 2100 Ma). The absence of detrital zircon of the ages similar to those of migmatitic gneisses (∼3200–2800 Ma) in Paleoproterozoic metasediments suggests their deposition distal from the Archean terranes followed by a tectonic assemblage of the SASCA domain during the later stages of the Eburnean orogeny.
... Carte géologique schématique du craton ouest-africain(Berger et al., 2013) ...
La zone nord de Toumodi est située dans la partie sud du sillon de Toumodi-Fètêkro, au centre de la Côte d’Ivoire. Cette zone étant fortement latéritisée, une cartographie à partir du régolithe en vue de l’amélioration des connaissances de la géologie de la partie sud du sillon de Toumodi-Fètêkro a été initiée. Elle s’est faite grâce à la télédétection et aux données de sondage réalisés dans la zone. Ainsi, il ressort de cette étude que le régolithe de la zone d’étude provient de l’altération supergène des différentes formations géologiques observées et se caractérise par un profond profil d'altération d’épaisseur moyenne d’environ 18 m avec une distribution spatiale de régolithe relique, d'érosion, de dépôt ainsi que des surfaces affectées par une latéritisation généralisée. The northern area of Toumodi is located in the southern part of the Toumodi-Fètêkro Trench in central Côte d'Ivoire. In order to improve knowledge of the regolith and geology of the southern part of the Toumodi-Fètêkro Trench, a regolith mapping study was initiated. This was done using remote sensing and borehole data from the area. Thus, it appears from this study that the regolith in the study area comes from the supergene alteration of the different geological units observed and is characterized by a deep alteration profile with an average thickness of about 18 m with a spatial distribution of relict regolith, erosion, deposition as well as surfaces affected by a generalized lateritization.
... Res. 10(10), 1050-1061 2 other hand to the east, the Eburnean domain (Berger et al., 2013;Kouamelan, 1996;Bessoles, 1977). The department of Sipilou -Biankouma is located in the west of the Ivory Coast in the Archean domain. ...
... As for the ultramafic rocks of South Sipilou, North Sipilou, North Biankouma which have not been dated, they could have been affected by the Archean granulite metamorphism (2.8 Ga) described in the region (Kouamelan, 1996, Gouedji, 2014 which induced these same characteristics to the rocks affected by this metamorphism. Thus, the ultramafic bed-rocks of South Sipilou could be of Archean age like certain intrusions described in West Africa in the Archean domain (layered intrusion of Guelb el Azib in Mauritania; Berger et al., 2013). ...
South Sipilou is an area containing lateritic nickel mineralization that developed on ultramafic rocks in the department of Sipilou-Biankouma in western Ivory Coast. The objective of this study was to characterize the petrography and hydrothermal alterations affecting these ultramafic bed-rocks and to understand their involvement in lateritic nickel mineralization. Then to compare them to the ultramafic rocks already characterized in the department of Sipilou-Biankouma. Thus, the macroscopic characterization of these rocks was carried out in the field. Then, microscopic observations on the petrography and the hydrothermal alterations were made on these rocks after the preparation of thin sections in the laboratory.The results indicated that the lithologies of the ultramafic bed-rocks of South Sipilou consist of strongly serpentinized dunites, more or less harzburgitic lherzolites and olivine orthopyroxenites. Their petrographic characteristics showed a similarity with the ultramafic bed-rocks of the nickel-bearing lateritic mineralization of North Biankouma, North Sipilou and differences with those of Samapleu, Yepleu, in the department of Sipilou-Biankouma. Also, the main hydrothermal alterations of the ultramafic rocks of South Sipilou are composed of silicification, carbonation and serpentinization. Only serpentinizationcontributed to the concentration of nickel in the bed-rock and within the lateritic profile.
... In comparison to their laterally extensive and better-preserved intracratonic counterparts, Archean layered intrusions in terranes along craton margins are less explored for their potential to host Ni-Cu sulphides, PGE, chromite and magnetite. The delimiting factors in exploration include the medium-high-grade (amphibolite-to granulite-facies) metamorphic overprint in the terranes, and the common occurrence of mafic-ultramafic rocks as fragmented units (Windley et al., 1981;Sills et al., 1982;Hatcher et al., 1984;Polat et al., 2012;Hoffmann et al., 2012;Berger et al., 2013;Bagas et al., 2016;Rajesh et al., 2020a;Anoop et al., 2022;Spier et al., 2022). Nevertheless, Archean layered complexes have the potential to host economically viable mineralization. ...
Ultramafic-mafic rocks in medium-to high-grade metamorphic terranes commonly occur as fragmented units of once continuous layered intrusions. A number of factors can complicate the delineation of the dismembered remnants and reconstruction of the original lithostratigraphy. This study focuses on remnant ultramafic rocks of the Mesoarchean Lechana layered complex in the southern Motloutse Complex, eastern Botswana. In view of the limited exposures, including the prominent cover rocks, geologic characterization was supplemented with geophysical techniques. The NE-SW traverse covered in the study includes the Tamasane and Sapolamorori hills, on either side of the cover rocks. Both hills are comprised of layered ultramafic rocks, with tonalite gneiss and amphibolite forming the surrounding rocks. The inferred layered lithostratigraphy includes serpentinized dunite, peridotite, peridotite-pyroxenite, pyroxenite-peridotite, and pyroxenite. Magnetitite seams constitute the main mineralization, and are associated with the serpentine-rich rocks. Aeromagnetic data provide insights into the bulk magnetic susceptibility of the ultramafic lithologies along the transect. The highest magnetic susceptibilities occur as semi-circular closed patches. The two anomalies at either end of the transect correlate with the layered ultramafic bodies at the Tamasane and Sapolamorori hills. The rest approximately correlates with high Ni ± Cr ± Cu soil anomalies reported from the region. This redefines the known extent of the Lechana layered complex beneath the cover rocks. The study highlights the potential of integrating geological and geophysical data to delineate the dismembered remnants of Archean layered complexes.
... The origin of Precambrian gabbro-anorthosite bodies has been variously interpreted as either invoking differentiation from a single magmatic lineage or as an outcome of several magmatic pulses. These are several proponents of a single magmatic differentiation history [28][29][30][31][32] . According to Weaver et al. 28 , the presence of hydrous phase (caused during melting of the depleted mantle) and crystal fractionation involving plagioclase cumulates play important roles in generating the gabbro-anorthosite (layered) complex. ...
... Moreover, Archean mafic volcanic rocks are associated with anorthosite-bearing layered intrusions that have calcic plagioclase megacrysts and magmatic amphibole and are often associated with chromitites, which are commonly linked with subduction-generated hydrous arc magmatism, and are considered to have formed mostly in Archean island arcs or some in continental arcs (Berger et al., 2013;Mohan et al., 2013;Piaia et al., 2017;Polat et al., 2009Polat et al., , 2018aSantosh and Li, 2018;. These examples demonstrate and confirm that Archean arc magmatism was global in scale. ...
Temporal variations in the incompatible trace element geochemistry of volcanic rocks in Archean greenstone belts have major implications for the style of tectonics that operated in the early Earth, and if and when plate tectonic processes occurred in the Archean, which are still subjects of substantial debate. Comparing the geochemistry of Archean volcanic rocks with that of Phanerozoic arc volcanic rocks has the potential to shed light on these questions. Geochemical data from 8,249 Eoarchean to Neoarchean volcanic rocks and 20,099 Phanerozoic arc volcanic rocks were compiled from the literature to address the above questions through the application of temporal incompatible trace element ratio variations, N-MORB-normalised trace element diagrams, and tectonic setting discrimination diagrams. The sampled rocks range in composition from ultramafic through basaltic and andesitic to dacitic/rhyolitic. Most of the incorporated Archean volcanic rocks were deemed to have been unaffected by significant alteration or crustal contamination in the literature and, therefore, to reflect their provenance, a feature that was corroborated by this study. Most of these Archean volcanic rocks plot in the plate margin, oceanic arc and continental arc fields in classification and tectonic setting discrimination diagrams, with the remainder plotting in the alkaline arc, mid-ocean ridge and oceanic island fields. Comparison between N-MORB-normalised trace element diagrams of volcanic rocks from well-studied Archean greenstone belts in Greenland, Canada, South Africa, China, Australia, India, Brazil and Finland and volcanic rocks from well-studied modern arcs demonstrates that their trace element patterns are remarkably similar. This indicates that the former formed in arc-related settings by modern-style plate tectonic processes that operated throughout the Archean. The Pb and Nb anomalies of most Archean volcanic rocks are fully consistent with an arc-related setting. The temporal variations in the incompatible trace element ratios of Archean volcanic rocks, coupled with their lithological associations, demonstrate that intra-oceanic arc magmatism was prominent in the Eoarchean before a shift in these ratios in the Paleoarchean signified the beginning of Andean-style continental arc magmatism between 3500 and 3200 Ma. Modern-style plate tectonic processes were a far more important contributor to Archean crustal growth and evolution than sagduction-driven vertical tectonic processes.
... Schematic geological map of the study area. (a) West African shield (adapted fromFigure 1(a) in reference[8]. (b) Man craton in western Ivory Coast (adapted fromFigure 2in[9]; the inset shows the Bounta area (in reference[7]). ...
... There are very few highgraded metamorphosed anorthositic igneous layered complexes, e.g. Fiskenaesset anorthositic complex in West Greenland (Rollinson et al., 2010), Guelb el Azib layered complex in West African craton, Mauritania (Berger et al., 2013), the Messina layered intrusion, Limpopo belt, South Africa, (Barton, 1996); all over the world where chromitites are interlayered with anorthosite of Archean age Konar, 2011, 2012;Talukdar et al., 2017). Sittampundi layered complex (SLC) is one of them showing rhythmic layering of smaller patches of chromitite within the anorthosite layer with pyroxenite and mafic rocks located at the Granulite Terrane of Southern India (GTSI) in Tamil Nadu (Subramaniam, 1956;Ramadurai et al., 1975). ...
The present study addresses a comparative analysis of the potentials of Airborne Visible and infrared imaging spectrometer -next generation (AVIRIS-NG) data, with respect to Landsat-8 Operational Land Imager (OLI) data for mapping of sporadic exposures of mafic cumulates within the anorthosite intrusion and delineation of major lithological units of Sittampundi layered complex. AVIRIS-NG and Landsat-8 OLI data were initially compared using scene-based relative signal-to-noise ratio (SNR) analysis. Subsequently, spectral anomaly maps were generated to map different lithological rock units using the constrained energy minimization (CEM) approach. Spectral maps derived using CEM were further filtered by low-pass filtering to control the false-positive result. Spectral angle mapper (SAM) classification technique was applied to analyze the suitability of AVIRIS-NG and Landsat-8 OLI data for lithological mapping. Confusion matrix analysis was carried out to assess the SAM classified maps. The first vertical derivative (FVD) map of magnetic anomaly and field evidence/geological exposures were used to validate the results. SNR analysis indicates the superior signal strength of AVIRIS-NG data than Landsat-8 OLI data. Moreover, combined analysis based on CEM and SAM of remote sensing data and FVD of magnetic anomaly reveals that the false-positive area indicating metagabbro/mafic cumulate is lower in AVIRIS-NG data than Landsat-8 OLI data. This is because of the relatively poor SNR, spectral and spatial resolutions of Landsat-8 OLI data; however, it can be good enough for mapping of metagabbro/mafic cumulate when AVIRIS-NG data is unavailable.
