Petrology of spinel lherzolite xenoliths and host basaltic lava from Ngao Voglar volcano, Adamawa Massif (Cameroon Volcanic Line, West Africa): equilibrium conditions and mantle characteristics

Nkouandou, Oumarou Faarouk; Temdjim, Robert

doi:10.3190/jgeosci.108

Cited by 15 publications

(16 citation statements)

References 31 publications

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“…7 Whole-rock major-and trace-element analyses of peralkaline rhyolites from Lake Chad The absence of a progressive age distribution (Fig. 4), which would be expected in the case of a plume (Fitton and Dunlop 1985), lead us to refute the hypothesis of a hot spot for the origin of the "Cameroon Hot Line", which was previously considered as a Cenozoic to present tectonomagmatic zone (Déruelle et al 2007;Nkouandou and Temdjim 2011). The situation must be reconsidered on the basis of the new dating of the Lake Chad volcanic rocks.…”

Section: Geochronological Implicationsmentioning

confidence: 89%

Petrology of the Late Cretaceous peralkaline rhyolites (pantellerite and comendite) from Lake Chad, Central Africa

Mbowou¹,

Lagmet²,

Nomade³

et al. 2012

J. Geosci.

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Late Cretaceous peralkaline rhyolites (69.4 ± 0.4 Ma -2σ analytical, 1.9 Ma full external uncertainty, 40 Ar/ 39Ar sanidine single crystal laser dating) from Lake Chad are the oldest lavas of the "Cameroon Hot Line". These lavas (pantellerite and comendite), consisting of quartz ± alkali feldspar ± fluoro-arfvedsonite ± augite-hedenbergite ± aegirine ± fayalite (Fa 97-99 ) and ilmenite, are characterized by a progressive increase in the total REE contents and the magnitude of the negative Eu anomaly owing to the alkali feldspar-dominated fractionation. Two groups of peralkaline rhyolites have been distinguished according to mineralogical and geochemical data. Both, group-1 (La N /Yb N : 8.4-9.0; Zr/Nb: ~ 8) and group-2 (La N /Yb N : 10.7-12.6; Zr/Nb: ~ 6) are genetically related. The peralkaline rhyolites from Lake Chad could not be solely the product of fractional crystallization from a basaltic parental magma. The influx of F-rich fluids could have greatly modified the composition of rhyolitic magmas as attested by the presence of fluoro-arfvedsonite.

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Section: Geochronological Implicationsmentioning

confidence: 89%

Petrology of the Late Cretaceous peralkaline rhyolites (pantellerite and comendite) from Lake Chad, Central Africa

Mbowou¹,

Lagmet²,

Nomade³

et al. 2012

J. Geosci.

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“…Samples recovered from kimberlites, lamproites and alkaline basalts have placed new constraints on the petrogenetic and geodynamic processes operating over the past 3.5 billion years (Shi et al, 1998;Wyman and Kerrich, 2010;Shirey and Richardson, 2011;Tang et al, 2013). These constraints have improved our understanding of plate tectonics, mantle plumes, and mantle composition (Ballhaus, 1993;Putirka, 1999;Beccaluva et al, 2004;Nkouandou and Temdjim, 2011;Shirey and Richardson, 2011) and provided insight into geodynamics, geochemistry, geophysics, and many other branches of Earth Sciences.…”

Section: Introductionmentioning

confidence: 99%

Lithospheric mantle xenoliths sampled by melts from upwelling asthenosphere: The Quaternary Tasse alkaline basalts of southeastern British Columbia, Canada

2016

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The Tasse basalts are exposed near the north shore of Quesnel Lake in southeastern British Columbia. They host a variety of mantle xenoliths consisting predominantly of spinel lherzolite with minor dunite and pyroxenite. Mineralogically, the xenoliths are composed of olivine, orthopyroxene, clinopyroxene and spinel characterized by forsterite (Fo 87-93), enstatite (En 90-92), diopside (En 45-50-Wo 40-45-Fs 5), and Cr-spinel (6−11 wt. % Cr), respectively. All of the mantle xenoliths are coarse-grained and show granoblastic textures. Clinopyroxene and spinel display textural evidence for chemical reactions with percolating melts. The mantle xenoliths are characterized by restricted Mg-numbers (89−92%) and low abundances of incompatible elements (Ba=2−11 ppm; Sr=3−31 ppm) and Yttrium (1−3 ppm). On the basis of REE patterns, the xenoliths are divided into three groups reflecting the various degrees of mantle metasomatism: (1) Group 1 consists of concave-up LREE patterns (La/Sm cn =0.48−1.16; Gd/Yb cn =0.71−0.92); (2) Group 2 possesses flat to moderately LREEenriched patterns (La/Sm cn =1.14−1.92; Gd/Yb cn =0.87−1.09); and (3) Group 3 is characterized by strongly LREE-enriched patterns (La/Sm cn =1.53−2.45; Gd/Yb cn =1.00−1.32). On MORBnormalized trace element diagrams, the majority of the xenolith samples share the enrichment of LILE (Rb, Ba, K), U, Th, Pb, Sr and the depletion of HFSE (Nb, Ta, Ti, Y) relative to REE. These geochemical characteristics are consistent with a compositionally heterogeneous subcontinental lithospheric mantle source that originated as sub-arc mantle wedge peridotite at a convergent plate margin. The Tasse basalts have alkalic compositions characterized by low SiO 2 (44−46 wt.%) and high alkali (Na 2 O+K 2 O=5.1−6.6 wt.%) contents. They are strongly enriched in incompatible elements (TiO 2 =2.4−3.1 wt.%; Ba=580−797 ppm; Sr=872−993 ppm) and, display OIB-like trace 3 element patterns (La/Sm n =3.15−3.85; Gd/Yb n =3.42−4.61). They have positive Nd (+3.8 to +5.5) values, with 338−426 Ma depleted mantle model ages, and display uniform OIB-like Sr (87 Sr/ 86 Sr=0.703346−0.703591) and Pb (206 Pb/ 204 Pb=19.40−19.58; 207 Pb/ 204 Pb=15.57−15.60; 208 Pb/ 204 Pb=38.99−39.14) isotopic compositions. The basalts erupted discontinuously along a >1000 km long SE-NW-trending linear belt with minimal compositional variation indicative of a homogenous mantle source. The Sr−Nd−Pb isotope and trace element systematics of the alkaline basalts suggests that they originated from partial melting of an upwelling asthenospheric mantle source. Melting of the asthenospheric mantle might have stemmed from extension of the overlying lithosphere in response to the early stages of back-arc basin opening in the Omineca and Intermontane belts. Ridge subduction beneath the Canadian Cordillera might have played an important role in the weakening of the lithospheric mantle prior to its extension. Alternatively, melting of the upwelling asthenosphere in response to the delamination of the lithospheric mantle beneath the Rocky M...

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“…The oceanic part comprises mainly undersaturated (Ngako et al ., ), while those of the continental part are undersaturated to oversaturated (Nkoumbou et al ., ). These volcanic rocks include basanites, alkali basalts, hawaiites, mugearites, benmoreites, trachytes, phonolites, and/or rhyolites (Rankenburg et al ., ; Kuepouo et al ., ; Kamgang et al ., , , , ; Njonfang et al ., ; Nkouandou & Temdjim, ). The age of some igneous rocks along CVL are presented in Table .…”

Section: Outline Of the Geology Of Source Areamentioning

confidence: 99%

U–Pb Ages for Zircon Grains from Nsanaragati Alluvial Gem Placers: Its Correlation to the Source Rocks

et al. 2015

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The Mamfe Basin is located in the SW of Cameroon and is an extension of the much bigger Benue Trough in the SE of Nigeria. Along the Asenem River and its tributaries in the western part of the Mamfe Basin (close to the border with Nigeria) gem placers yielding big zircon grains were found in recent river sediments close to Nsanaragati. In order to determine the source area and to establish a possible correlation between the zircons found in the Nsanaragati placers and rocks surrounding the Mamfe Basin 56 detrital zircon grains were analysed regarding their U-Pb ages and selected trace element contents by LA-ICP-MS techniques. Possible source areas are rocks from the Benue Trough in the West and from the Cameroon Volcanic Line (CVL) in the SE of the study area. Based on microscopic analyses it was possible to distinguish two groups of zircons: reddish and non-reddish ones, where the latter group comprises color variations from brown to orange, yellow to even colorless. In general, the detrital zircons show high hafnium values (4576 to 12565 ppm) and very variable thorium (7.8 to 1565 ppm) and uranium values (13.4 to 687 ppm). The Th/U ratios vary from 0.4 to 2.3, allowing correlations for some zircon grains to kimberlitic, granitic or syenitic affinities. It was also possible to distinguish zircon grains crystallised in mafic mantle-derived melts from those crystallised in felsic melts, e.g. from continental rift-related magmatic systems. In general, the U-Pb zircon ages obtained range from 11.7 to 1949 Ma. All zircons of the reddish group yielded almost similar ages resulting in a Concordia age of 12.4 Ma (Serravallian), an age unknown from the Mamfe Basin so far. The group of non-reddish zircons showed various ages ranging from Serravallian to Orosirian. It was possible to correlate the youngest ages with rocks known from intrusions along the CVL, dated with K/Ar or Ar/Ar methods. The most probable sources were Mount Bamenda and Mount Bambouto in the east of the Mamfe Basin. Cretaceous ages are interpreted as re-recycled clastic sediments whose original source had been rocks in the south and the north of the Benue Trough and who had been eroded and deposited within the catchment area of the Asenem river system in the Mamfe Basin in post-Cretaceous times. The oldest ages are assumed to represent the pan-African and pre-pan-African basement of the Mamfe basin.

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Petrology of spinel lherzolite xenoliths and host basaltic lava from Ngao Voglar volcano, Adamawa Massif (Cameroon Volcanic Line, West Africa): equilibrium conditions and mantle characteristics

Cited by 15 publications

References 31 publications

Petrology of the Late Cretaceous peralkaline rhyolites (pantellerite and comendite) from Lake Chad, Central Africa

Petrology of the Late Cretaceous peralkaline rhyolites (pantellerite and comendite) from Lake Chad, Central Africa

Lithospheric mantle xenoliths sampled by melts from upwelling asthenosphere: The Quaternary Tasse alkaline basalts of southeastern British Columbia, Canada

U–Pb Ages for Zircon Grains from Nsanaragati Alluvial Gem Placers: Its Correlation to the Source Rocks

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