Ultramafic xenoliths from Lake Nyos area, Cameroon volcanic line, West-central Africa: Petrography, mineral chemistry, equilibration conditions and metasomatic features

Temdjim, Robert

doi:10.1016/j.chemer.2011.07.002

Cited by 35 publications

(23 citation statements)

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“…The data presented in this paper are the first detailed account on the Befang site xenoliths. The modal composition of the xenoliths as well as the chemical characteristics of minerals are similar to those presented in prior xenolith studies in the OVG (Lee et al 1996;Liu et al 2017Liu et al , 2020Pintér et al 2015;Temdjim 2012). Our study additionally takes into account the deformation fabric of Asaah et al 2015).…”

Section: Introductionsupporting

confidence: 69%

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Lithospheric mantle refertilization by DMM-derived melts beneath the Cameroon Volcanic Line—a case study of the Befang xenolith suite (Oku Volcanic Group, Cameroon)

Tedonkenfack

Puziewicz

Aulbach

et al. 2021

Contrib Mineral Petrol

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The origin and evolution of subcontinental lithospheric mantle (SCLM) are important issues of Earth’s chemical and physical evolution. Here, we report detailed textural and chemical analyses on a mantle xenolith suite from Befang (Oku Volcanic Group, Cameroon Volcanic Line), which represents a major tectono-magmatic structure of the African plate. The samples are sourced from spinel-facies mantle and are dominated by lherzolites. Their texture is cataclastic to porphyroclastic, and foliation defined by grain-size variation and alignment of spinel occurs in part of peridotites. Spinel is interstitial and has amoeboidal shape. Clinopyroxene REE patterns are similar to those of Depleted MORB Mantle (DMM) except LREEs, which vary from depleted to enriched. The A-type olivine fabric occurs in the subset of one harzburgite and 7 lherzolites studied by EBSD. Orthopyroxene shows deformation consistent with olivine. The fabric of LREE-enriched clinopyroxene is equivalent to those of orthopyroxene and olivine, whereas spinel and LREE-depleted clinopyroxene are oriented independently of host rock fabric. The textural, chemical and thermobarometric constraints indicate that the Befang mantle section was refertilised by MORB-like melt at pressures of 1.0–1.4 GPa and temperatures slightly above 1200–1275 °C. The olivine-orthopyroxene framework and LREE-enriched clinopyroxene preserve the protolith fabric. In contrast, the LREE-depleted clinopyroxene, showing discordant deformation relative to the olivine-orthopyroxene protolith framework, and amoeboidal spinel crystallized from the infiltrating melt. The major element and REEs composition of minerals forming the Befang peridotites indicate subsequent reequilibration at temperatures 930–1000 °C. This was followed by the formation of websterite veins in the lithospheric mantle, which can be linked to Cenozoic volcanism in the Cameroon Volcanic Line that also brought the xenoliths to the surface. This study therefore supports the origin of fertile SCLM via refertilization rather than by extraction of small melt fractions, and further emphasizes the involvement of depleted melts in this process.

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Section: Introductionsupporting

confidence: 69%

“…The other published xenolith data from the OVG refer to the Lake Nyos site (Liu et al 2017(Liu et al , 2020Pintér et al 2015;Temdjim 2012), which is located several kilometres from Befang (Fig. 1b).…”

Section: Previous Xenolith Studies In the Oku Volcanic Groupmentioning

confidence: 99%

Lithospheric mantle refertilization by DMM-derived melts beneath the Cameroon Volcanic Line—a case study of the Befang xenolith suite (Oku Volcanic Group, Cameroon)

Tedonkenfack

Puziewicz

Aulbach

et al. 2021

Contrib Mineral Petrol

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“…The geology of LNC has been investigated in detail in previous studies (e.g., Fitton and Dunlop, 1985;Kling et al, 1987;Lockwood and Rubin, 1989;Aka et al, 2008;Temdjim, 2012;Fantong et al, 2015). Their results show that the catchment is made up of granitic rocks (quartz monzonite) of Precambrian age which are intensively fractured and weathered and faulted.…”

Section: Geological and Hydrogeological Settingsmentioning

confidence: 94%

A multi-tracer approach for assessing the origin, apparent age and recharge mechanism of shallow groundwater in the Lake Nyos catchment, Northwest, Cameroon

Kamtchueng

Fantong

Wirmvem

et al. 2015

Journal of Hydrology

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Keywords:Stable isotopes (d 18 O and dD) CFCs and SF 6 Shallow groundwater origin and age Shallow groundwater recharge Lake Nyos -Cameroon s u m m a r yThe shallow aquifer in the vicinity of Lake Nyos (Northwest, Cameroon) is one of the main water supply sources to meet the water needs of the inhabitants to be resettled after 1986s tragedy. Unfortunately, there is a lack of knowledge on the groundwater recharge and flow systems in the area. Multiple environmental tracers (d 18 O, dD, Cl À , CFCs and SF 6 ) and a yearly record of rainfall, surface waters and groundwater were employed to characterize the recharge mechanism of the shallow groundwater seeping in the fractured rock of the Lake Nyos catchment (LNC). The d 18 O-dD relationship of the rainfall events gave the Nyos Meteoric Water Line: dD = 8.28 d 18 O + 11.87. Inland moisture vapor may have impacted the isotopic composition of original vapor masses from Gulf of Guinea prior to precipitation. Shallow groundwater in the LNC shows a similar trend of enrichment in 18 O and D as surface waters indicating a well-mixed aquifer. The proportions of surface waters and rainfall in the groundwater reservoir were 87% and 13%, respectively. The high annual recharge rate (941 mm/yr) and the seasonal variability in the isotopic signatures of groundwater indicate a renewable aquifer system. CFCs apparent ages-based piston flow model revealed a young age (average of 24 a.) of the groundwater in the LNC. SF 6 -based ages were biased young as compared to relatively younger than CFCs-based ages, implying an additional terrigenic production of SF 6 . The conceptual model for groundwater flow suggests that three main flow regimes, mainly controlled by the physical properties of the rock heterogeneities govern the movement of water in the aquifer. The piston flow model appears, however, to be the better model to explain the flow regime in the highly faulted and fissured area where recharge occurs ($1200-1600 masl). The rapid circulation and the low solubility lead to low mineralization. In the middle-lower area where waters circulate more in the weathered layer, exponential mixing model dominates, yielding more mineralized water. Downward to the valley, with prevailing gentle slope, interaction between surface and recently infiltrated groundwater better explain the observed similarity in the isotopic compositions and the mineralization of water.

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“…This source is suspected to have high Zr/Hf ratio of 46.2 and low Nb/Ta ratio of 13.75 averaging the CT46 and EB20 values. Considering the set of mafic lavas, Nb/Ta remains constant with variable Zr/Hf, a feature of OIB and MORB fields that is usually explained by pyroxene fractionation (Pfänder et al, 2007 and2012). However, the petrographical relationships show that the Zr/Hf ratio decreases with Zr from mafic to evolved lavas.…”

Section: Source Characteristics and Degree Of Partial Melting 21mentioning

confidence: 96%

“…It is consistent with the location of the Manengouba magma source in the spinel-garnet transition zone and in the amphibole field. The existence of an amphibole-bearing upper mantle beneath the CVL is supported by the sampling of amphibole-spinel-garnet ultramafic xenoliths in volcanoes of Ngaoundéré,Lake Nyos, Oku, and Mount Cameroon (Lee et al 1996;Temdjim et al, 2004; Matsukage and Oya, 2010;Temdjim, 2012). After Marzoli et al(2000), trace element patterns agree with an amphibole-bearing source for Sr-rich mafic rocks of the Bambouto volcano.…”

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confidence: 89%

The Mount Manengouba, a complex volcano of the Cameroon Line: Volcanic history, petrological and geochemical features

Pouclet¹,

Dongmo

Bardintzeff

et al. 2014

Journal of African Earth Sciences

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International audienceThe volcanic story of Mount Manengouba is related to four chronological stages: (1) forming of the early Manengouba shield volcano between 1.55 and 0.94 Ma, (2) building of the Eboga strato-cone between 0.94 and 0.89 Ma, (3) caldera collapse and silicic extrusions of the Elengoum Complex between 0.89 and 0.70 Ma, and (4) intra-caldera and flank activity between 0.45 and 0.11 Ma. The volume of the volcano is calculated at 320 km3 ± 5%. The volcanic rocks are attributed to two magmatic outputs. The first and main magma generation produced the shield volcano, the strato-cone, and the syn- to post-caldera extrusions, displaying a complete series from basanites to trachytes (magmatic Group 1). The second magma generation is limited to the late and flank activity evolving from basanites to trachy-phonolite (magmatic Group 2). Both magmatic groups belong to the under-saturated alkaline sodic series. Petrological calculations locate the magmatic reservoir between 37 and 39 km in the upper mantle for the Group 1 lavas, and between 42 and 44 km for the Group 2 lavas. Trachytes were generated in a secondary crustal reservoir. Magmatic series evolve with medium to low pressure fractional crystallization of olivine, pyroxene, oxides, feldspar, and apatite. Significant crustal assimilation is evidenced in trachytes. The magma of Group 1 was generated with 3-6% of partial melting of a moderately enriched source containing 3-7% of garnet. Melting took place in the spinel to garnet transition zone located at 70-90 km and around 25 kb. The magma of Group 2 resulted from a slightly higher partial melting from a less garnet-rich source that indicates uprising of the melting column in the upper part of transition zone. Sr, Nd, and Pb isotope data of the Manengouba rocks and neighboring lavas are analyzed and compared with those of the mafic lavas of the CVL. Three source components are distinguished: a depleted component originated from the asthenospheric swell, a radiogenic component linked to the contaminated lithosphere of the Neoproterozoic mobile belt, and an enriched component or the lithosphere possibly related to pre-rifting magmatic processes

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Ultramafic xenoliths from Lake Nyos area, Cameroon volcanic line, West-central Africa: Petrography, mineral chemistry, equilibration conditions and metasomatic features

Cited by 35 publications

References 97 publications

Lithospheric mantle refertilization by DMM-derived melts beneath the Cameroon Volcanic Line—a case study of the Befang xenolith suite (Oku Volcanic Group, Cameroon)

Lithospheric mantle refertilization by DMM-derived melts beneath the Cameroon Volcanic Line—a case study of the Befang xenolith suite (Oku Volcanic Group, Cameroon)

A multi-tracer approach for assessing the origin, apparent age and recharge mechanism of shallow groundwater in the Lake Nyos catchment, Northwest, Cameroon

The Mount Manengouba, a complex volcano of the Cameroon Line: Volcanic history, petrological and geochemical features

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