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11.
Sadrack Felix Toteu Rose Yongue Fouateu Joseph Penaye Jacqueline Tchakounte Aubin Ciriaque Seme Mouangue William Randall Van Schmus Etienne Deloule Henrik Stendal 《Journal of African Earth Sciences》2006,44(4-5):479
TIMS-ID and SIMS U–Pb dating on zircons from metaplutonic rocks involved in the Pan-African nappe of southern Cameroon allow definition of three groups of subduction-related intrusions: group-I intrusions represented by the Masins metagabbro in the Lomie region yielded 666 ± 26 Ma; group-II intrusions represented by the Mamb metasyenogabbro and the Yaoundé pyriclasite yielded ca. 620 Ma and are broadly coeval with the deposition of the Yaoundé metasediments; group-III intrusions represented by the Elon augen metagranite and the Ngaa Mbappe metamonzodiorite yielded ca. 600 Ma. The onset of the nappe tectonics occurred under high-grade conditions in the range 616 to 610 Ma and continued around 600 Ma with the emplacement of the shallowest nappes. Finally, the construction of southern Cameroon proceeded by a multi-stage evolution characterized by a long-lived development of magmatic arcs associated with rapid opening and closure of sedimentary marginal basins in relation to a northward subduction. 相似文献
12.
R. Tchameni A. Pouclet J. Penaye A.A. Ganwa S.F. Toteu 《Journal of African Earth Sciences》2006,44(4-5):511
The Nagoundéré Pan-African granitoids in Central North Cameroon belong to a regional-scale massif, which is referred to as the Adamawa-Yade batholith. The granites were emplaced into a ca. 2.1 Ga remobilised basement composed of metasedimentary and meta-igneous rocks that later underwent medium- to high-grade Pan-African metamorphism. The granitoids comprise three groups: the hornblende–biotite granitoids (HBGs), the biotite ± muscovite granitoids (BMGs), and the biotite granitoids (BGs). New Th–U–Pb monazite data on the BMGs and BGs confirm their late Neoproterozoic emplacement age (ca. 615 ± 27 Ma for the BMGs and ca. 575 Ma for the BGs) during the time interval of the regional tectono-metamorphic event in North Cameroon. The BMGs also show the presence of ca. 926 Ma inheritances, suggesting an early Neoproterozoic component in their protolith.The HBGs are characterized by high Ba–Sr, and low K2O/Na2O ratios. They show fairly fractionated REE patterns (LaN/YbN 6–22) with no Eu anomalies. The BMGs are characterized by higher K2O/Na2O and Rb/Sr ratios. They are more REE-fractionated (LaN/YbN = 17–168) with strong negative Eu anomalies (Eu/Eu* = 0.2–0.5). The BGs are characterized by high SiO2 with K2O/Na2O > 1. They show moderated fractionated REE patterns (LaN/YbN = 11–37) with strong Eu negative anomalies (Eu/Eu* = 0.2–0.8) and flat HREE features (GdN/YbN = 1.5–2.2). In Primitive Mantle-normalized multi-element diagrams, the patterns of all rocks show enrichment in LILE relative to HFSE and display negative Nb–Ta and Ti anomalies. All the granitoids belong to high-K calc-alkaline suites and have an I-type signature.Major and trace element data of the HBGs are consistent with differentiation of a mafic magma from an enriched subcontinental lithospheric mantle, with possible crustal assimilation. In contrast, the high Th content, the LREE-enrichment, and the presence of inherited monazite suggest that the BGs and BMGs were derived from melting of the middle continental crust. Structural and petrochemical data indicate that these granitoids were emplaced in both syn- to post-collision tectonic settings. 相似文献
13.
We present the first grating-resolution X-ray spectra of the Seyfert 1 galaxy NGC 3783, obtained with the High Energy Transmission Grating Spectrometer on the Chandra X-Ray Observatory. These spectra reveal many narrow absorption lines from the H-like and He-like ions of O, Ne, Mg, Si, S, and Ar as well as Fe xvii-Fe xxi L-shell lines. We have also identified several weak emission lines, mainly from O and Ne. The absorption lines are blueshifted by a mean velocity of approximately 440+/-200 km s-1 and are not resolved, indicating a velocity dispersion within the absorbing gas of a few hundred kilometers per second or less. We measure the lines' equivalent widths and compare them with the predictions of photoionization models. The best-fitting model has a microturbulence velocity of 150 km s-1 and a hydrogen column density of 1.3x1022 cm-2. The measured blueshifts and inferred velocity dispersions of the X-ray absorption lines are consistent with those of the strongest UV absorption lines observed in this object. However, simple models that propose to strictly unify the X-ray and UV absorbers have difficulty explaining simultaneously the X-ray and UV absorption-line strengths. 相似文献
14.
Smart C. Obiora Anthony Chukwu Sadrack F. Toteu Theophilus C. Davies 《Journal of the Geological Society of India》2016,87(4):453-462
Mining activities have been undertaken for over 95 years in Enyigba area of southeastern Nigeria. In this area, thirty-six (36) trace metals including those that are essential for plant and animal nutrition have been analyzed from forty-nine (49) soil samples that were collected from three Pb-Zn mines. The aim of the analysis is to assess the level of contamination of the soils caused by mining activities. Potentially harmful elements which are commonly associated with Pb-Zn mines were of special interest. Such elements included Pb, Zn, As, Cd, Mn, Fe, Se, Sb, Cu and Bi. Generally, the samples analyzed showed elevated concentrations of Pb, Zn, Cd, Cu and Cr when compared with concentrations documented in the international agricultural soil standards. Geo-accumulation indices of soils that occur closer to the mines indicate moderate to extreme level of contamination in Pb and moderate levels in Cd. Enrichment factor (EF) showed very high enrichment to extremely high enrichment in Pb. Cd and Zn enrichment were found to be significant and moderate respectively. Conversely, the geo-accumulation indices for soil samples located away from the mines indicate moderate to heavy contamination in Pb but had moderate to significant enrichment in Cd and moderate in Bi and Cr. In general, soil quality all around the mines were found to have deteriorated as revealed by the pollution load index. Thus the results of this study call for immediate remedial measures to be initiated. In addition, miners and local communities living around the mines need to be enlightened about the dangers of exposure to these heavy metal contaminants. 相似文献
15.
Henrik Stendal Sadrack Flix Toteu Robert Frei Joseph Penaye Urbain Olivier Njel Jean Bassahak Jean Nni Boniface Kankeu Vincent Ngako Joseph Victor Hell 《Journal of African Earth Sciences》2006,44(4-5):443
Rutile, as an important component in alluvial or eluvial heavy mineral deposits, is known in southern Cameroon. These deposits are underlain by the Neoproterozoic low- to high-grade Yaoundé Group. Geochemical, thermometric, fluid inclusion and Pb isotopic studies of the rutile from alluvial and eluvial concentrates and from medium-grade micaschist from the nearby Yaoundé region permit the following conclusions: (1) alluvial and eluvial rutile of the Yaoundé region are derived from the degradation of metapelites, metamafic rocks and pegmatites of the nearby Yaoundé Group; (2) rutile in the Yaoundé Group formed during the Pan-African metamorphism, or was inherited as detrital rutile from a 900 Ma source. The study also shows that the rutile can be used to trace the history of the Pan-African belt north of the Congo craton. 相似文献
16.
Joseph Penaye Alfred Krner Sadrack F. Toteu William R. Van Schmus Jean-Claude Doumnang 《Journal of African Earth Sciences》2006,44(4-5):530
The Mayo Kebbi region in SW Chad is part of the NNE-SSW trending Neoproterozoic Central African Fold Belt (CAFB) and is made up of three calc-alkaline granitoid suites emplaced into a metavolcanic–metasedimentary sequence. The first suite is represented by mafic to intermediate rocks (gabbro-diorite and metadiorite) emplaced between 737 and 723 Ma during early Pan-African convergence. The second consists of the Mayo Kebbi batholith and includes tonalites, trondhjemites and granodiorites, emplaced during several magmatic pulses between 665 and 640 Ma. The third suite includes porphyritic granodiorite and hypersthene monzodiorite dated at ca. 570 Ma. The Mayo Kebbi domain extends southward into Cameroon and is interpreted as a middle Neoproterozoic arc stabilized at ca. 650 Ma. This study also revealed a diachronous evolution between Mayo Kebbi and western Cameroon (e.g., the Poli region). The overall evolution of this part of the CAFB is interpreted as the result of successive development of magmatic arcs, since ca. 740 Ma, and tectonic collage of three different domains (Adamawa-Yade, Mayo Kebbi, and West Cameroon) which, after suturing, were intruded by post-collisional granitoids (<600 Ma). 相似文献
17.
S. F. Toteu Garoua J. Macaudiere J. M. Bertrand D. Dautel 《International Journal of Earth Sciences》1990,79(3):777-788
Morphoscopic studies of zircons, including optical microscopic and SEM (backscattered electron mode), from the Rôniers valley (West-Poli, Northern Cameroon) indicate an important crystallization of zircon during a medium-grade garnet-kyanite metamorphic event. This was associated with a deformation (D1) and with the emplacement of a basic and intermediate plutonic suite (BIP). U-Pb dating of these zircon gave almost concordant Pan-African ages (630 Ma) which contribute to a solution of a major regional uncertainty about the age of the regional D1 event, which, in the mobile belt of Central Africa, has been considered previously either as Pan-African or as Lower to Middle Proterozoic. A chronological framework is proposed for the evolution of northern Cameroon.
Zusammenfassung Eine kristallmorphologische Bearbeitung von Zirkonen aus Glimmerschiefern des Rôniers-Tals (Westlich von Poli, Nord-Kamerun) wurde mit Durchlicht- und mit RasterElektronen-Mikroskopie (Rückstrahl Elektronen) ausgeführt. Verbunden mit einer Bearbeitung des strukturgeologischen und metamorphen Rahmens führt sie zu der Vorstellung einer massiven Auskristallisation der Zirkone anläßlich eines tektono-metamorphen Ereignisses mittlerer Stärke in der Granat-Disthen Fazies. Dieses Ereigniss ist von einer Deformationsphase (D1) und der Platznahme eines basischen bis intermediären Gesteinsverbandes (BIP) begleitet worden. Eine U/Pb Datierung dieser Zirkone ergibt praktisch konkordante pan-afrikanische Alter (630 M.J.) Diese Resultate klären eine Ungewissheit in Bezug auf das Alter des stärksten metamorphen Schieferung, die hier als Resultat des Ereignisses D1 gedeutet wird. Je nach der geographischen Stellung innerhalb der zentral-afrikanischen mobilen Zone wurde bis jetzt das Alter dieser Schieferung als pan-afrikanisch oder als unter- bis mittelproterozoisch gegeben. Ein chronologischer Ablauf kann somit für die Entwicklung des nordkamerunischen Gebietes vorgeschlagen werden.
Résumé Une étude morphologique de zircons provenant des micaschistes de la vallée des Rôniers (ouest de Poli, Nord Cameroun) a été menée aussi bien en microscopie optique qu'en microscopie à balayage (électrons rétrodiffusés). Combinée à l'étude de l'environnement structural et métamorphique, elle conduit à l'idée d'une cristallisation massive du zircon pendant un événement tectono-métamorphique de degré moyen dans le faciès à grenat-disthène. Cet épisode s'accompagne d'une phase de déformation (D1) et de la mise en place d'une association basique à intermédiaire (BIP). Une datation U/Pb de ces zircons donne des âges panafricains (630 Ma) pratiquement concordants. Ces résultats permettent de lever une ambiguïté sur l'âge de la foliation métamorphique principale interprétée comme résultant de l'événement D1: elle est considérée selon les endroits de la zone mobile d'Afrique centrale soit d'âge panafricain soit d'âge protérozoïque inférieur à moyen. Une chronologie de l'évolution du domaine nord camerounais est proposée.
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18.
J.P. Milesi S.F. Toteu Y. Deschamps J.L. Feybesse C. Lerouge A. Cocherie J. Penaye R. Tchameni G. Moloto-A-Kenguemba H.A.B. Kampunzu N. Nicol E. Duguey J.M. Leistel M. Saint-Martin F. Ralay C. Heinry V. Bouchot J.C. Doumnang Mbaigane V. Kanda Kula F. Chene J. Monthel P. Boutin J. Cailteux 《Journal of African Earth Sciences》2006,44(4-5):571
This paper is prepared within the frameworks of IGCP Project 470 and the associated BRGM scientific project “Africa 1999–2004” to accompany the 1:4,000,000 scale map “Geology and major ore deposits of Central Africa, presented at the 20th Colloquium of African Geology in Orleans in June 2004. It incorporates geological and metallogenic data from eight countries in Central Africa (Angola, Cameroon, Chad, Central African Republic, Congo Brazzaville, Democratic Republic of Congo (DRC), Equatorial Guinea and Zambia). The map is a harmonised and geo-referenced preliminary map, based on a GIS at 1:2,000,000 scale, and focusses on the spatial and temporal distribution of selected major deposits. 相似文献
19.
岩浆侵入体对有机质生烃(成熟)作用的影响及数值模拟 总被引：3，自引：1，他引：2
火山作用带来的热源对有机质的成烃进程和成烃量产生了重要影响,这种热效应一方面可以加速烃源岩的成熟和成烃作用,另一方面可以破坏先期形成的油藏。目前国内外对火山作用的生烃热效应方面的研究主要在热成熟度参数变化描述及岩浆侵入体引起的围岩热蚀变程度的讨论。火山作用对成烃/成藏的利弊,影响的时/空范围、程度的定量研究尚未报道。本次在前人研究基础上,建立了描述岩浆侵入体散热的热传导模型,进一步结合EasyRo%模型和前人报道的实测Ro数据进行了模型检验。通过调整模型的参数和岩浆侵入体厚度、位置及个数等进行了火山作用对有机质成熟作用及生烃影响的研究。模拟结果表明:岩浆侵入体的热作用范围是有限的,但是不同地质情况,影响的范围广度也不相同,对于相同厚度的侵入体,初始温度越高,作用范围越广,但是一般X/D3(X/D代表离接触面的距离与侵入体厚度的比值)。对于不同厚度侵入体而言,在侵入体热作用影响的范围内,侵入体越厚,热作用的范围越广。同时数值模拟结果也表明岩浆侵入体的存在可以改变烃源岩生烃期。 相似文献