Journal ArticleDOI
Petrology of ophiolites of Memel, Nsimè-Kellé and Mapan (Yaoundé group): Evidence of the geodynamic evolution of the Pan-African orogeny in South Cameroon
Okia Mukete Kundu,D. Minyem,Jules Tamen,Charles Nkoumbou,Calistus Gentry Fuh,Numbem Jacqueline Tchakounte +5 more
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In this paper , the authors show that most ophiolite compositions are either Cr-rich with high FeO/Fe2O3 values (peridotitic spinels) or Cr-poor with low FeO or Fe2O2O 3 values (melt-derived or magmatic spinels).Abstract:
Ophiolites are the remnants of ancient oceanic crust that can serve as tools to reconstruct the evolutionary history of fossil oceans. At Boumnyebel, the western part of the Yaoundé group, the sole of the lower unit (magnesian mica-schists and gneiss) of the Pan-African nappes is made up of ophiolitic rocks (talc schists, chlorite schists, serpentinites, amphibolites, pyroxenites, hornblendites). Structurally, the lower unit has a flat-lying schistosity with some recumbent folds while the underlying TTG gneisses are marked by a high-dipping foliation at Mapan. The contact between the Pan-African mica schists and the basement formations (Congo craton) is therefore discordant. In ophiolitic rocks, amphibole is actinolite, tremolite or magnesio-riebeckite. Chlorite compositions correspond to clinochlore. Talc shows notable substitution of Mg by Fe whereas substitution of Mg by Fe and Al prevails in serpentine. Spinel compositions are either Cr-rich with high FeO/Fe2O3 values (peridotitic spinels) or Cr-poor with low FeO/Fe2O3 values (melt-derived or magmatic spinels). Main mineral features indicate a metamorphic retromorphosis of the original lherzolites, harzburgites, dunites and pyroxenites to hornblendites and serpentinites. This is followed by hydrothermal alteration (at various temperatures: 250–570 °C and low pressure: < 2 kbar) that yielded chlorite schists and talc schists. Chemically, talc schists are made up of SiO2, MgO and minor FeO and Al2O3, while chlorite schists and hornblendites contain notable amounts of Al2O3 and CaO, respectively. All the ultramafic rocks display the same range of high Ni, Cr, Co contents with various LREE enrichments but flat HREE patterns. Multi-element patterns show that most talc schist are depleted in almost all elements. All the ultramafic rocks are marked by deep Nb, Ta, K, Pb, Sr, Ti, Zr and Hf troughs suggesting that the ultramafic rocks possibly derived from heterogeneous mantle sources varying from fertile to refractory peridotites. Amphibolites are generated from N-MORB, IAT or CA geotectonic settings. The compositions of spinel and ultramafic whole rocks reveal an arc setting that has evolved from divergent plate setting (oceanisation, N-MORB) to convergent plate (IAT, CA, SSZ D-MORB) settings. In summary, ophiolites emplaced in various geotectonic settings and were amalgamated during the Pan-African collision. read more
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Relics of ophiolite-bearing accretionary wedges in NE Brazil and NW Africa: connecting threads of western Gondwana´s ocean during Neoproterozoic times
Lauro Cézar Montefalco de Lira Santos,Fabrício de Andrade Caxito,M. Houketchang Bouyo,Sonia Ouadahi,Kawther Araïbia,Geysson de Almeida Lages,Glenda Lira Santos,João Paulo Araujo Pitombeira,Peter A. Cawood +8 more
TL;DR: In this article , geophysical, structural and petrological data suggest that the complex network of shear zones that once connected the Borborema province (NE Brazil), Tuareg shield (Hoggar) and Central African domain (NW Africa) likely represent ancient sutures that mark collisional episodes between Archean-Paleoproterozoic paleocontinents such as Amazonian-West African and São Francisco-Congo.
Journal ArticleDOI
Geological study of a Mewoulou-Nkolbisson ductile strike-slip fault segment (Western Yaoundé, Cameroon): evidence of hazards related to structural landforms
V. Metang,B. Tassongwa,Nomo Negue Emmanuel,Henri Appolinaire Kenzo,Steve Franck Bamou-Wandji,Brigitte Domkam,Dior-Christelle Mboutchouang,Diane Marilyn Nkamga Mbakam,Léa Grace Tene Kengne,Lucas Mouafo +9 more
Journal ArticleDOI
Petrography and geochemistry of the Sanaga river sediments, central Cameroon: Constraints on weathering, provenance, and tectonic setting
Patrice Roland Liyouck,Gabriel Ngueutchoua,John S. Armstrong-Altrin,A. Sonfack,Yannick Steve Kontchipe Ngagoum,Armel Zacharie Ekoa Bessa,V. Ambassa Bela,Duviol Arcange Tsanga,Armand Sylvain Ludovic Wouatong +8 more
TL;DR: In this article , the origin of alluviums and tectonic setting of source rocks were inferred from stream sediments of the Sanaga River (SR) in central Cameroon.
References
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Chemical and isotopic systematics of oceanic basalt : implications for mantle composition and processes
TL;DR: In this article, trace-element data for mid-ocean ridge basalts and ocean island basalts are used to formulate chemical systematics for oceanic basalts, interpreted in terms of partial-melting conditions, variations in residual mineralogy, involvement of subducted sediment, recycling of oceanic lithosphere and processes within the low velocity zone.
Journal ArticleDOI
The composition of the Earth
William F. McDonough,Shen-Su Sun +1 more
TL;DR: In this paper, the authors compared the relative abundances of the refractory elements in carbonaceous, ordinary, and enstatite chondritic meteorites and found that the most consistent composition of the Earth's core is derived from the seismic profile and its interpretation, compared with primitive meteorites, and chemical and petrological models of peridotite-basalt melting relationships.
Journal ArticleDOI
Nomenclature of amphiboles Report of the Subcommittee on Amphiboles of the International Mineralogical Association Commission on New Minerals and Mineral Names;Nomenclature of amphiboles Report of the Subcommittee on Amphiboles of the International Mineralogical Association Commission on New Minerals and Mineral Names
Bernard Elgey Leake,Alan R. Woolley,C. E. S. Arps,William D. Birch,M. C. Gilbert,Joel D. Grice,Ec. Hawthorne,A. Kato,Hanan J. Kisch,V. G. Krivovichev,K. Linthout,J. Laird,Joseph A. Mandarino,W. V. Maresch,Ernest H. Nickel,N. M. S. Rock,John C. Schumacher,D. C. Smith,Nicholas C.N. Stephenson,Luciano Ungaretti,Eric J.W. Whittaker,G. Youzhi +21 more
TL;DR: The International Mineralogical Association's approved amphibole nomenclature has been revised to simplify it, make it more consistent with divisions generally at 50%, define prefixes and modifiers more precisely, and include new amphibole species discovered and named since 1978, when the previous scheme was approved.
Book Chapter
Trace element characteristics of lavas from destructive plate boundaries
TL;DR: In this paper, discrimination diagrams are drawn which highlight these various characteristics and therefore enable volcanic arc basalts to he recognized in cases where geological evidence is ambiguous, and the results indicate that the Oman ophiolite complex was made up of back-arc oceanic crust intruded by the products of volcanic arc magmatism.
Journal ArticleDOI
Major and trace element composition of the depleted MORB mantle (DMM)
R. Workman,Stanley R. Hart +1 more
TL;DR: Asimow et al. as mentioned in this paper derived an estimate for the chemical composition of the depleted MORB mantle (DMM), the source reservoir to mid-ocean ridge basalts (MORBs), which represents at least 30% the mass of the whole silicate Earth.