Cameroon Line alkaline magmatism (central Africa): A reappraisal

Njonfang, Emmanuel; Nono, Alexandre; Kamgang, Pierre; Ngako, Vincent; Tchoua, Félix M.

doi:10.1130/2011.2478(09)

Cited by 27 publications

(29 citation statements)

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“…Petrological data also show that hawaiite and basanite alkali basaltic volcanism is commonplace along the CVL. These low‐volume, high‐pressure lavas suggest that little shallow (crustal) fractionation of magma is occurring beneath the line prior to eruption [e.g., Fitton and Dunlop , 1985; Halliday et al , 1988; Marzoli et al , 2000; Suh et al , 2003; Yokoyama et al , 2007; Déruelle et al , 2007; Njonfang et al , 2011; Teitchou et al , 2011].…”

Section: Introductionmentioning

confidence: 99%

The development of magmatism along the Cameroon Volcanic Line: Evidence from teleseismic receiver functions

Gallacher¹,

Bastow²

2012

Tectonics

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[1] The Cameroon Volcanic Line (CVL) in West Africa is a chain of Cenozoic volcanism with no clear age progression. The reasons for its existence are unclear, and the nature of its magmatic plumbing system is poorly understood. Specifically, whether or not the CVL crust presently contains melt and/or mafic intrusions, as is often observed at hot spots and rifts elsewhere, is presently unknown. To address this issue, we present a receiver function study of crustal structure using earthquakes recorded by the Cameroon Broadband Seismic Experiment. In regions of the CVL unaffected by Cretaceous extension associated with the breakup of Gondwana (e.g., the Garoua rift), Vp/Vs ratios are markedly low (network average $1.74) compared to hot spots elsewhere, providing no evidence for either melt or cooled mafic crustal intrusions due to CVL magmatism. The character of P-to-S conversions from beneath the CVL also indicates that lower-crustal intrusions (often termed underplate) are not present beneath the region. Our observations thus corroborate earlier petrological studies that show CVL alkaline magmas fractionate in the mantle, not the crust, prior to eruption. Hypotheses for the formation of the CVL should not include markedly elevated upper-mantle potential temperatures, or large volumes of partial melt, both of which can explain observations at hot spots and rifts worldwide. The protracted, yet sporadic, development of small-volume alkali melts beneath the CVL may instead be explained better by lower melt volume mechanisms such as shear zone reactivation or lithospheric delamination.Citation: Gallacher, R. J., and I. D. Bastow (2012), The development of magmatism along the Cameroon Volcanic Line: Evidence from teleseismic receiver functions, Tectonics, 31, TC3018,

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Section: Introductionmentioning

confidence: 99%

The development of magmatism along the Cameroon Volcanic Line: Evidence from teleseismic receiver functions

Gallacher¹,

Bastow²

2012

Tectonics

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“…The CVL may be due to a more complex interaction between a hotspot and Precambrian faults [30]. A gravity study of the southern part of the Adamawa plateau has shown a belt of dense rocks at an average depth of 8 km running parallel to the Foumban shear zone.…”

Section: Discussionmentioning

confidence: 99%

Gravity Interpretation of the Cameroon Mountain (West Central Africa) Based on the New and Existing Data

Kenfack¹,

Tadjou²,

Kamguia³

et al. 2011

IJG

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A new gravity survey of the Mount Cameroon area has enabled the definition of four major gravimetric domains, which coincide with the recognized structural units. In order to determine the nature of superficial and deep structures in this mountainous zone, new gravity data have been processed. These new gravity data was integrated to existing gravity data to propose the new complete Bouguer anomaly map of the region, and then to show major characteristics of the Bouguer gravity of this area. The interpretation of gravity patterns (bouguer maps) in terms of geological data, shows that the Mount Cameroon zone belongs to a wide positive anomaly; these anomalies display complex gravity domains, which seem to be similar to that due to major structural units in the region and volcanic activity of the mountain. In the mountain active zone in particular (between 2000 and 3800 m of altitude), the new anomaly map shows high gravity anomalies (from 11 to 60 mgal), coupled with low gravity at some stations (in the summit, 4060 m) where gravity anomaly is about -30 mgal. The steep WNW-ESE gravity gradients observed on the gravity maps mark the transition between positive in the south and negative anomalies.

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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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Cameroon Line alkaline magmatism (central Africa): A reappraisal

Cited by 27 publications

References 0 publications

The development of magmatism along the Cameroon Volcanic Line: Evidence from teleseismic receiver functions

The development of magmatism along the Cameroon Volcanic Line: Evidence from teleseismic receiver functions

Gravity Interpretation of the Cameroon Mountain (West Central Africa) Based on the New and Existing Data

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

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