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Journal articles on the topic 'Eburnean orogeny'

Author: Grafiati

Published: 4 June 2021

Last updated: 10 February 2022

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1

Baratoux, Lenka, Václav Metelka, Séta Naba, Mark W. Jessell, Michel Grégoire, and Jérôme Ganne. "Juvenile Paleoproterozoic crust evolution during the Eburnean orogeny (∼2.2–2.0Ga), western Burkina Faso." Precambrian Research 191, no. 1-2 (November 2011): 18–45. http://dx.doi.org/10.1016/j.precamres.2011.08.010.

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2

Bouchot, Vincent, and Jean-Louis Feybesse. "Palaeoproterozoic gold mineralization of the Etéké Archaean greenstone belt (Gabon): its relation to the Eburnean orogeny." Precambrian Research 77, no. 3-4 (April 1996): 143–59. http://dx.doi.org/10.1016/0301-9268(95)00047-x.

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3

Block, S., J. Ganne, L. Baratoux, A. Zeh, L. A. Parra-Avila, M. Jessell, L. Ailleres, and L. Siebenaller. "Petrological and geochronological constraints on lower crust exhumation during Paleoproterozoic (Eburnean) orogeny, NW Ghana, West African Craton." Journal of Metamorphic Geology 33, no. 5 (April 3, 2015): 463–94. http://dx.doi.org/10.1111/jmg.12129.

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4

Weber, Francis, François Gauthier-Lafaye, Hubert Whitechurch, Marc Ulrich, and Abderrazak El Albani. "The 2-Ga Eburnean Orogeny in Gabon and the opening of the Francevillian intracratonic basins: A review." Comptes Rendus Geoscience 348, no. 8 (November 2016): 572–86. http://dx.doi.org/10.1016/j.crte.2016.07.003.

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5

Aidoo, Felix, Prosper M. Nude, Fang-Yuan Sun, Ting Liang, and Shao-Bing Zhang. "Paleoproterozoic TTG-like metagranites from the Dahomeyide Belt, Ghana: Constraints on the evolution of the Birimian-Eburnean Orogeny." Precambrian Research 353 (February 2021): 106024. http://dx.doi.org/10.1016/j.precamres.2020.106024.

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6

Ganne, J., M. Gerbault, and S. Block. "Thermo-mechanical modeling of lower crust exhumation—Constraints from the metamorphic record of the Palaeoproterozoic Eburnean orogeny, West African Craton." Precambrian Research 243 (April 2014): 88–109. http://dx.doi.org/10.1016/j.precamres.2013.12.016.

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7

Kanouo, Nguo Sylvestre, David Richard Lentz, Khin Zaw, Charles Makoundi, Emmanuel Afanga Archelaus Basua, Rose Fouateu Yongué, and Emmanuel Njonfang. "New Insights into Pre-to-Post Ediacaran Zircon Fingerprinting of the Mamfe PanAfrican Basement, SW Cameroon: A Possible Link with Rocks in SE Nigeria and the Borborema Province of NE Brazil." Minerals 11, no. 9 (August 30, 2021): 943. http://dx.doi.org/10.3390/min11090943.

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The pre- to post-Late Neoproterozoic geological histories in the south to southwestern part of Mamfe Basin (SW Cameroon) were reported following analysis of the zircon crystals from their host rocks. A genetic model was developed for the zircon host rocks’ formation conditions, and the registered post-emplacement events were presented. The obtained ages were correlated with the data available for rocks in the Cameroon Mobile Belt, SE Nigeria, and the Borborema Province of NE Brazil. Separated zircons from Araru black to whitish gneiss, Araru whitish-grey gneiss, and Mboifong migmatite were analyzed for their morphology and texture U-Th-Pb composition, and U-Pb ages. Published U-Pb zircon ages for Otu granitic pegmatite, Babi mica schist, and Nkogho I-type anatectic granite were updated. Zircon ages in Araru black to whitish gneiss; Araru whitish-grey, Mboifong migmatite, Babi mica schist, Nkogho I-type anatectic granite, and Otu granitic pegmatite date the Eburnean tectono-magmatic/metamorphic event in Cameroon and SE Nigeria. The Late Paleoproterozoic to Early Mesoproterozoic ages record extensional (continental rift) settings and anorogenic magmatism in the Borborema Province in the NE of Brazil. These ages date collisional phases between the São Francisco–Congo and West African cratons and the Saharan metacraton with metamorphism and magmatism in Cameroon. They also date the Kibarian tectono-magmatic/metamorphism and PanAfrican tectono-magmatic/metamorphism in SE Nigeria. The Late Paleoproterozoic to Early Mesoproterozoic ages date the Cariris Velhos orogeny in the Borborema Province in NE Brazil, with Early Tonian crustal rifting, magmatism, and metamorphism and the collisional phase of the Brasiliano orogeny with syn-collisional plutons and extensive shear zoning and post-collisional granite intrusions.

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8

Block, Sylvain, Mark Jessell, Laurent Aillères, Lenka Baratoux, Olivier Bruguier, Armin Zeh, Delphine Bosch, Renaud Caby, and Emmanuel Mensah. "Lower crust exhumation during Paleoproterozoic (Eburnean) orogeny, NW Ghana, West African Craton: Interplay of coeval contractional deformation and extensional gravitational collapse." Precambrian Research 274 (March 2016): 82–109. http://dx.doi.org/10.1016/j.precamres.2015.10.014.

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9

McFarlane, H. B., L. Ailleres, P. Betts, J. Ganne, L. Baratoux, M. W. Jessell, and S. Block. "Episodic collisional orogenesis and lower crust exhumation during the Palaeoproterozoic Eburnean Orogeny: Evidence from the Sefwi Greenstone Belt, West African Craton." Precambrian Research 325 (June 2019): 88–110. http://dx.doi.org/10.1016/j.precamres.2019.02.012.

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10

Debat, Pierre, Serge Nikiéma, Alain Mercier, Martin Lompo, Didier Béziat, François Bourges, Martin Roddaz, Stefano Salvi, Francis Tollon, and Urbain Wenmenga. "A new metamorphic constraint for the Eburnean orogeny from Paleoproterozoic formations of the Man shield (Aribinda and Tampelga countries, Burkina Faso)." Precambrian Research 123, no. 1 (May 20, 2003): 47–65. http://dx.doi.org/10.1016/s0301-9268(03)00046-9.

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11

Kouamelan, Alain Nicaise, Kouassi Serge Auguste Kra, Sagbrou Chérubin Djro, Jean-Louis Paquette, and Jean-Jacques Peucat. "The Logoualé Band: A large Archean crustal block in the Kenema-Man domain (Man-Leo rise, West African Craton) remobilized during Eburnean orogeny (2.05 Ga)." Journal of African Earth Sciences 148 (December 2018): 6–13. http://dx.doi.org/10.1016/j.jafrearsci.2017.09.004.

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12

Fotze, Quentin Marc Anaba, Charles Antoine Basseka, Anatole Eugene Djieto Lordon, Albert Eyike Yomba, Yves Shandini, and Jean Marie Tadjou. "Geophysical Data Processing for the Delineation of Tectonic Lineaments in South Cameroon." Earth Science Research 8, no. 2 (March 25, 2019): 1. http://dx.doi.org/10.5539/esr.v8n2p1.

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The processing of aeromagnetic and gravity data of the Northern part of Congo Craton (South Cameroon region), between latitudes 2°30’-3°30’ N and longitudes 12°-13° E, permitted the determination of the structural features ccurring within the Precambrian basement (Ntem Complex) southwards and the Pan-African belt (Yaounde Group) northwards. The maxima of the Horizontal Gradient within the study area, were obtained using the Blakely and Simpson method (1986). Those maxima were used to trace the magnetic lineaments of the study area. Furthermore, the Total Horizontal derivative of the Tilt derivative applied on the residual grid of Bouguer anomaly guaranteed the enhancement of linear structures which were automatically extracted using the CET Grid Analysis algorithm. The superimposition of both magnetic and gravity lineaments allowed us to display the structural framework of the area, whose major trending directions are E-W, ENE-WSW, and NE-SW. These major lineament directions are likely to be linked to one or more than a single tectonic event such as the ENE-WSW/NE-SW trends, considered as the subduction direction of the Congo craton beneath the Pan-African belt. These trends may be linked to the Eburnean orogeny and are also said to be connected to the Central African Shear Zone (CASZ). The geophysical lineaments identified in the study are defined as potential targets along which mineralization may have been formed, considering the economic potential of the area.

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13

Chardon, Dominique, Ousmane Bamba, and Kalidou Traoré. "Eburnean deformation pattern of Burkina Faso and the tectonic significance of shear zones in the West African craton." BSGF - Earth Sciences Bulletin 191 (2020): 2. http://dx.doi.org/10.1051/bsgf/2020001.

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Shear zones of the Paleoproterozoic Eburnean accretionary Orogen (West African craton) are investigated by means of large-scale structural mapping. Regional scale (10-100 km) mapping was based on the aeromagnetic survey of Burkina Faso and craton-scale (1000 km) mapping on a compilation of fabric data. At both scales, shear zones are arranged as an anastomosed transpressional network that accommodated distributed shortening and lateral flow of the orogenic lithosphere between the converging Kénéma-Man and Congo Archean provinces. Structural interference patterns at both scales were due to three-dimensional partitioning of progressive transpressional deformation and interactions among shear zones that absorbed heterogeneities in the regional flow patterns while maintaining the connectivity of the shear zone network. Such orogen-scale kinematic patterns call for caution in using the deformation phase approach without considering the “bigger structural picture” and interpreting displacement history of individual shear zones in terms of plate kinematics. The West African shear zone pattern is linked to that of the Guiana shield through a new transatlantic correlation to produce an integrated kinematic model of the Eburnean-Transamazonian orogen.

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14

Soulaimani, Abderrahmane, Mohamed Bouabdelli, and Alain Piqué. "The Upper Neoproterozoic-Lower Cambrian continental extension in the Anti-Atlas (Morocco)." Bulletin de la Société Géologique de France 174, no. 1 (January 1, 2003): 83–92. http://dx.doi.org/10.2113/174.1.83.

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Abstract Introduction. – In the Anti-Atlas, south of Morocco (fig. 1), the Precambrian terrains are usually divided into several “series” (fig. 2) : the Paleoproterozoic (PI) is an old crystalline basement, at least Eburnean ; the Neoproterozoic (PII) is constituted by metasedimentary rocks, quartzites and limestones, indicative of a shelf, in which volcano-sedimentary and volcanic flows are intercalated, laterally grading to an ophiolitic complex along the Sirwa-Bou Azzer axis. These PII rocks have been deformed in the course of the Panafrican orogeny ; above the underlying upper Proterozoic terrains and in major unconformity on the Panafrican structures, the Saghro group (PII3) and Ouarzazate group (PIII) series are volcanic and volcano-clastic sequences, often considered as late-Panafrican molasses. Above them, the Tata group (Adoudounian), constituted by marine carbonates and siltstones, represents the earliest Cambrian. Recent structural and sedimentological observations Recent observations have been realized through all the Anti-Atlas, of which the present note gives only examples that are the most significant and easily accessible. They show that the PII3 conglomerates were not everywhere deposited around Panafrican paleoreliefs ; they often contain large bodies of quartzites embedded within the conglomerates (fig. 3). Clearly, the PII3 is an olistostrome at the base of the PIII détrital and volcanic series, which were deposited at the base of active faults. The development of these reliefs took place several tens of millions of years after the end of the Panafrican paroxysm and therefore the PII3 and the PIII are post-Panafrican deposits, unrelated to the Panafrican orogeny. Study of synsedimentary structures (folds, faults, progressive unconformities : fig. 4 to 7) reveals the extensive character of this faulting event that extends even in basal Cambrian. Between the PII3 series and PIII an angular unconformity due to tilting can exist, but we did not find there plicative structures clearly related to the compressive late-Panafrican « B2 » phase sometimes described in the litterature. In the western Anti-Atlas, the extension is pure, with a NW-SE direction ; it is N-S in the central Anti-Atlas and it is transtensive according to N070°E faults, en échelon between sinistral N110°E trending faults in the central-eastern Anti-Atlas. In the detail, nevertheless, the synsedimentary structures suggest slidings from raised zones that correspond to the future inliers (fig. 7). Magmatic and metallogenic activity This extension accompanies various events : (1) a marine transgression, from west to east ; (2) the emplacement of extrusive magmas, first calco-alkaline then tholeiitic ; (3) an hydrothermal activity responsible for the concentration of Co, Au, Cu, etc. These concentrations were in the past attributed to various episodes, from the pre-Panafrican extension to the Hercynian compression. In fact, they result from the circulation of hydrothermal solutions that deposited, in the superficial levels of the crust, products extracted from the PIII magmas or the PII Proterozoic serpentines. The circulations took place in the old compressive structures (e.g. the Panafrican foliation) reopened during the extensive episode described above. Discussion and conclusion : the late Proterozoic-early Cambrian rifting The crustal extension that affected the Anti-Atlas started during the late Proterozoic, after the end of the main Panafrican deformation. Its tectonic significance is discussed with regard to the Panafrican orogeny : either a late Panafrican extension, bracketed between two compressive deformations and possibly related to a thinning of the orogenic crust, or a post-Panafrican extension, unrelated to compressive phases, described as a synrift event. In the Anti-Atlas, it developed through late Proterozoic and early Cambrian times. It aborted at the end of the early Cambrian. Evidences of a comparable extension are found in northern Morocco, western Europe and as far in the Middle East, i.e. all along the northern margin of the paleo-Gondwana.

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15

Lemoine, S., P. Tempier, J. P. Bassot, M. Caen-Vachette, Y. Vialette, S. Touré, and U. Wenmenga. "The Burkinian orogenic cycle, precursor of the Eburnian orogeny in West Africa." Geological Journal 25, no. 2 (April 1990): 171–88. http://dx.doi.org/10.1002/gj.3350250208.

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16

Bertrand, Jean Michel, and Emmanuel Ferraz Jardim de Sá. "Where are the Eburnian–Transamazonian collisional belts?" Canadian Journal of Earth Sciences 27, no. 10 (October 1, 1990): 1382–93. http://dx.doi.org/10.1139/e90-148.

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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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17

Tairou, Mahaman Sani, Pascal Affaton, Solomon Anum, and Thomas Jules Fleury. "Pan-African Paleostresses and Reactivation of the Eburnean Basement Complex in Southeast Ghana (West Africa)." Journal of Geological Research 2012 (July 17, 2012): 1–15. http://dx.doi.org/10.1155/2012/938927.

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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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18

Liégeois, J. P., W. Claessens, D. Camara, and J. Klerkx. "Short-lived Eburnian orogeny in southern Mali. Geology, tectonics, U-Pb and Rb-Sr geochronology." Precambrian Research 50, no. 1-2 (April 1991): 111–36. http://dx.doi.org/10.1016/0301-9268(91)90050-k.

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19

WALDRON, JOHN W. F., DAVID I. SCHOFIELD, GRAHAM PEARSON, CHIRANJEEB SARKAR, YAN LUO, and ROBERT DOKKEN. "Detrital zircon characterization of early Cambrian sandstones from East Avalonia and SE Ireland: implications for terrane affinities in the peri-Gondwanan Caledonides." Geological Magazine 156, no. 07 (July 16, 2018): 1217–32. http://dx.doi.org/10.1017/s0016756818000407.

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AbstractThe Caledonides of Britain and Ireland include terranes attributed to both Laurentian and Gondwanan sources, separated along the Solway line. Gondwanan elements to the south have been variably assigned to the domains Ganderia and East Avalonia. The Midland Platform forms the core of East Avalonia but its provenance is poorly known. Laser ablation split-stream analysis yields information about detrital zircon provenance by providing simultaneous U–Pb and Lu–Hf data from the same ablated volume. A sample of Red Callavia Sandstone from uppermost Cambrian Stage 3 of the Midland Platform yields a U–Pb age spectrum dominated by Neoproterozoic and Palaeoproterozoic sources, resembling those in the Welsh Basin, the Meguma Terrane of Nova Scotia and NW Africa. Initial εHf values suggest that the Neoproterozoic zircon component was derived mainly from crustal sources < 2 Ga, and imply that the more evolved Palaeoproterozoic grains were transported into the basin from an older source terrane, probably the Eburnean Orogen of West Africa. A sample from Cambrian Stage 4 in the Bray Group of the Leinster–Lakesman Terrane shows, in contrast, a distribution of both U–Pb ages and εHf values closely similar to those of the Gander Terrane in Newfoundland and other terranes attributed to Ganderia, interpreted to be derived from the margin of Amazonia. East Avalonia is clearly distinct from Ganderia, but shows evidence for older crustal components not present in West Avalonia of Newfoundland. These three components of the Appalachian–Caledonide Orogen came from distinct sources on the margin of Cambrian Gondwana.

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20

Caen-Vachette, M., and A. C. Umeji. "Geology and geochronology of the Okene area: evidence for an Eburnean orogenic cycle in south-central Nigeria." Journal of African Earth Sciences (and the Middle East) 7, no. 1 (January 1988): 121–26. http://dx.doi.org/10.1016/0899-5362(88)90058-9.

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21

Loose, Denny, and Volker Schenk. "2.09 Ga old eclogites in the Eburnian-Transamazonian orogen of southern Cameroon: Significance for Palaeoproterozoic plate tectonics." Precambrian Research 304 (January 2018): 1–11. http://dx.doi.org/10.1016/j.precamres.2017.10.018.

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22

Peucat, Jean-Jacques, Ramon Capdevila, Amar Drareni, Yamina Mahdjoub, and Mohamed Kahoui. "The Eglab massif in the West African Craton (Algeria), an original segment of the Eburnean orogenic belt: petrology, geochemistry and geochronology." Precambrian Research 136, no. 3-4 (February 2005): 309–52. http://dx.doi.org/10.1016/j.precamres.2004.12.002.

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23

D’Lemos, R. S., J. D. Inglis, and S. D. Samson. "A newly discovered orogenic event in Morocco: Neoproterozic ages for supposed Eburnean basement of the Bou Azzer inlier, Anti-Atlas Mountains." Precambrian Research 147, no. 1-2 (June 2006): 65–78. http://dx.doi.org/10.1016/j.precamres.2006.02.003.

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24

DOSTAL, J., J. D. KEPPIE, M. A. HAMILTON, E. M. AARAB, J. P. LEFORT, and J. B. MURPHY. "Crustal xenoliths in Triassic lamprophyre dykes in western Morocco: tectonic implications for the Rheic Ocean suture." Geological Magazine 142, no. 2 (March 2005): 159–72. http://dx.doi.org/10.1017/s0016756805000440.

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Dykes of calc-alkaline lamprophyre cutting granite of the Hercynian Jebilet Massif of the Moroccan Meseta (western Morocco) contain crustal xenoliths. The xenoliths range in composition from mafic (cognate cumulates) and upper crustal granitic rocks through gneisses to middle crustal felsic granulites. SHRIMP U–Th–Pb zircon analyses of these rocks indicate that the dykes were likely intruded during Middle Triassic times (∼235 Ma), whereas the xenoliths contain zircons with concordant Carboniferous–Early Permian, Neoproterozoic and Palaeoproterozoic ages (280–328 Ma, c. 540–615 Ma, 700 Ma and ∼2000 Ma). The 280–328 Ma ages appear to record synchronous intrusive and high-grade (up to granulite facies) Variscan metamorphic events, suggesting that high-grade metamorphism may have facilitated the S-type granitic magmatism. On the other hand, the ∼540–615 Ma, 700 Ma and 2000 Ma ages correspond with Pan-African and Eburnian orogenic events recorded in the West African Craton. In a Triassic reconstruction, Morocco is juxtaposed against Nova Scotia (Canada), and some have proposed that the basement of the easternmost terrane (Meguma terrane) is a piece of the West African craton. However, lower crustal xenoliths from Devonian dykes (∼370 Ma) cutting the Meguma terrane have yielded Late Devonian, Neo- and Mesoproterozoic ages (378 Ma, 575–629 Ma, ∼880–1050 Ma and ∼1530 Ma). The presence of ∼1 Ga ages suggests that the basement of the Meguma terrane is Avalonian rather than West African, implying that in a Pangean reconstruction, the Rheic Ocean suture between NW Africa and Maritime Canada coincides with the Atlantic Ocean.

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25

El Aouli, El Hassan, Dominique Gasquet, and Moha Ikenne. "Le magmatisme basique de la boutonniere d'Igherm (Anti-Atlas occidental, Maroc); un jalon des distensions neoproterozoiques sur la bordure nord du craton ouest-africain." Bulletin de la Société Géologique de France 172, no. 3 (May 1, 2001): 309–17. http://dx.doi.org/10.2113/172.3.309.

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Abstract In the Igherm inlier (western Anti-Atlas, Morocco) doleritic dyke swarms with various directions and gabbroic intrusive bodies were emplaced during Neoproterozoic times, cutting across either Eburnean micaschists and granites or Panafrican limestones and quartzites. All these rocks were deformed by the main Panafrican schistosity and covered by molassic and volcanic Upper Neoproterozoic series. The primary mineralogical assemblages (plagioclase, augite, olivine...) of the mafic rocks are nearly completely replaced by secondary assemblages (albite, actinolite, chlorite, epidote, calcite, quartz, leucoxene, magnetite, hematite...). However, three main groups have been recognized by the means of relative chronology and petrography. The group 1 is earlier, as shown by the intrusive character of the dykes of the other two groups into its gabbroic bodies. Using incompatible trace elements and rare earth elements it appears that this magmatism is truly heterogeneous and that the three groups have different magmatic affinities. The group 1 corresponds to tholeiitic dolerites and gabbros characterized by intersertal and ophitic textures and by high contents in Fe 2 O 3 (12.16 to 16.64%), TiO 2 (1.46 to 2.5%), Zr (90 to 174 ppm), Nb (7 to 13 ppm), Y (21.68 to 38.74 ppm) and V (264 to 419 ppm). The REE contents are low (Sigma REE = 49 to 137 ppm) and the REE patterns are flat [1.99<(La/Yb) N <4.56] showing a relative slight enrichment in LREE and no anomaly in Eu (0.89>Eu/Eu (super *) <1.11). These features as the TiO 2 vs FeO (super *) /MgO and V vs Ti/1000 diagrams are characteristic of anorogenic intraplate magmas. The group 2 corresponds to calc-alkaline dolerites and gabbros showing fine-grained intersertal textures and high contents of Al 2 O 3 (14.10 to 20.64%) and low contents of Fe 2 O 3 (8.35 to 12.91%), TiO 2 (0.68 to 1.41%), Zr (66 to 106 ppm), Nb (5 to 7 ppm), Y (16.41 to 20.75 ppm) and V (144 to 264 ppm). The REE contents vary from 67 to 155 ppm and the REE patterns are fractionated (2.78<(La/Yb) N <6.62) with a strong enrichment in LREE. The slight positive Eu anomaly (0.91<Eu/Eu (super *) <1.37) is related to the wealth of plagioclases frequently observed in these rocks. The TiO 2 contents of these rocks and their low FeO (super *) /MgO ratios give them a calc-alkaline affinity similar to that of calc-alkaline orogenic basalts related to an oceanic subduction. The group 3 corresponds to alkaline dolerites characterized by fine-grained intersertal textures with high contents of TiO 2 (3.85 to 3.97%), P 2 O 5 (0.66 to 0.77%), Nb (33 to 39 ppm), Zr (262 to 287 ppm), Y (39.6 to 47.7 ppm) and REE (Sigma REE = 205 to 218 ppm). The REE patterns are fractionated (7.77<La/Yb) N <6.65) without no Eu anomaly (0.99<Eu/Eu (super *) <1.02). The Ti/V and Y/Nb ratios (65.26 to 74.95 and 1.19 to 1.22, respectively) are those of alkaline rocks found in intraplate environments. The detailed petrographical, geochemical and field studies of the Igherm inlier show that the mafic magmatism is more complex than previously described. The mafic tholeiitic and alkaline magmatism occurring in the Igherm inlier is also present in the other inliers of the Moroccan Anti-Atlas during Neoproterozoic times. On the other hand the calc-alkaline Neoproterozoic mafic magmatism is very rare elsewhere in the Anti-Atlas except in the Siroua Massif and locally in the Bas Draa and Tagragra d'Akka inliers (western Anti-Atlas). The geodynamical environment of this mafic magmatism is linked to a strong extensional tectonic regime occurring at the northern border of the West African craton during Neoproterozoic times. This regime is related to the oceanic opening described in Central Anti-Atlas and to the emplacement of the ophiolites of Bou Azzer and Siroua or occurs immediately after the oceanic opening. The chemical heterogeneities observed in the three defined groups can be related to heterogeneities of mantellic sources and/or various partial melting ratios of the sub-continental mantle. We can assume that this major fissural magmatic event, not precisely dated, is equivalent to that observed in the other Neoproterozoic provinces in Hoggar, Cameroon, north America and Brazil.

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Owona, Sébastien, Lothar Ratschbacher, Gulzar Afzal M, Moussa Nsangou Ngapna, Joseph Mvondo Ondoa, and Georges Emmanuel Ekodeck. "New U–Pb zircon ages of Nyong Complex meta‐plutonites: Implications for the Eburnean/ Trans‐Amazonian Orogeny in southwestern Cameroon (Central Africa)." Geological Journal, October 22, 2020. http://dx.doi.org/10.1002/gj.4022.

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27

Djoukouo Soh, Arlette Pulcherie, Sylvestre Ganno, Lianchang Zhang, Landry Soh Tamehe, Changle Wang, Zidong Peng, Xiaoxue Tong, and Jean Paul Nzenti. "Origin, tectonic environment and age of the Bibole banded iron formations, northwestern Congo Craton, Cameroon: geochemical and geochronological constraints." Geological Magazine, September 10, 2021, 1–19. http://dx.doi.org/10.1017/s0016756821000765.

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Abstract The newly discovered Bibole banded iron formations are located within the Nyong Group at the northwest of the Congo Craton in Cameroon. The Bibole banded iron formations comprise oxide (quartz-magnetite) and mixed oxide-silicate (chlorite-magnetite) facies banded iron formations, which are interbedded with felsic gneiss, phyllite and quartz-chlorite schist. Geochemical studies of the quartz-magnetite banded iron formations and chlorite-magnetite banded iron formations reveal that they are composed of >95 wt % Fe2O3 plus SiO2 and have low concentrations of Al2O3, TiO2 and high field strength elements. This indicates that the Bibole banded iron formations were not significantly contaminated by detrital materials. Post-Archaean Australian Shale–normalized rare earth element and yttrium patterns are characterized by positive La and Y anomalies, a relative depletion of light rare earth elements compared to heavy rare earth elements and positive Eu anomalies (average of 1.86 and 1.15 for the quartz-magnetite banded iron formations and chlorite-magnetite banded iron formations, respectively), suggesting the influence of low-temperature hydrothermal fluids and seawater. The quartz-magnetite banded iron formations display true negative Ce anomalies, while the chlorite-magnetite banded iron formations lack Ce anomalies. Combined with their distinct Eu anomalies consistent with Algoma- and Superior-type banded iron formations, we suggest that the Bibole banded iron formations were deposited under oxic to suboxic conditions in an extensional basin. SIMS U–Pb data indicate that the Bibole banded iron formations were deposited at 2466 Ma and experienced metamorphism and metasomatism at 2078 Ma during the Eburnean/Trans-Amazonian orogeny. Overall, these findings suggest that the studied banded iron formations probably marked the onset of the rise of atmospheric oxygen, also known as the Great Oxidation Event in the Congo Craton.

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