Mineralogical and geochemical fingerprints of mantle metasomatism beneath Nyos volcano (Cameroon volcanic line)

Teitchou, Merlin Isidore; Grégoire, Marilaure; Temdjim, Robert; Ghogomu, R.T.; Ngwa, Caroline Neh; Aka, Festus Tongwa

doi:10.1130/2011.2478(10)

Cited by 11 publications

(11 citation statements)

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“…6C, D), high LILE and negative Nb and Ta anomalies. These features are similar to those reported for mantle xenoliths from East Oman and Cameroon that have been metasomatised by CO 2 -rich and Na-bearing mafic silicate melts (Grégoire et al, 2009;Teitchou et al, 2011) as well as by alkali (silica-undersaturated and nepheline normative) basalts as described by Laurora et al (2001) and Rivalenti et al (2004) for Gobernador Gregores peridotite xenoliths. In fact, Gobernador Gregores Group 3 lherzolites (samples GG-05, GG-10, GG-13) exhibit a stronger LREE/HREE fractionation and a strong negative Ti and moderately negative Zr and Hf anomalies, which is also compatible with metasomatism caused by CO 2 -rich and Na-bearing mafic silicate melts at relatively low melt/rock ratios.…”

Section: Evidence Of Modal and Cryptic Volatile-rich Metasomatismsupporting

confidence: 84%

Highly siderophile elements mobility in the subcontinental lithospheric mantle beneath southern Patagonia

Tassara

Gonzáléz-Jiménez

Reich

et al. 2018

Lithos

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Peridotite xenoliths collected from alkali basalts in the Argentinian Patagonia reveal the existence of an ancient depleted Paleoproterozoic mantle that records a subsequent multistage metasomatic history. Metasomatism is associated with carbonatite-like melts that evolved, after variable melt/rock ratio interaction, towards CO 2 -rich and Na-bearing Mg-rich (mafic) silicate, and volatile-rich alkali silicate melts. High degrees of partial melting produced strongly depleted mantle domains devoid of base-metal sulphides (BMS). Moderate degrees of partial melting and later unrelated metasomatism produced a range of slightly depleted, slightly enriched, and strongly enriched mantle domains that preserve different types of BMS. Thus, six different BMS populations were identified including typical residual Type 1A BMS enriched in Os, Ir, and Ru relative to Pt, Pd, and Au located within primary olivine and clinopyroxene, and metasomatic Type 2A BMS that are relatively enriched in Pt, Pd, Au occurring as interstitial grains. Reworking of these two types of BMS by later metasomatism resulted in the formation of a new generation of BMS (Type 1B and Type 2B) that are intimately associated with carbonate/apatite blebs and/or empty vesicles, as well as with cryptically metasomatised or metasomatic clinopyroxene. These newly formed BMS were re-enriched in Os, Pd, Au, Re and in semi-metal elements (As, Se, Sb, Bi, Te) compared to their Type 1A and Type 2A precursors. A third generation of BMS corresponds to Ni-Cu immiscible sulphide mattes entrained within Na-bearing silica under-saturated alkali melt. They occur systematically related to intergranular glass veins and exhibit distinctively near flat CI-chondrite normalised highly siderophile element patterns with either positive Pd (Type 3A) or negative Pt (Type 3B) anomalies. Our findings indicate that Os, Pd, Re and Au can be selectively transported by volatile-rich alkali silicate melts in the subcontinental lithospheric mantle. Moreover, the transport of sulphide mattes entrained in silicate melts is also an effective mechanism to produce HSE endowment in the SCLM and play an important role as precursors of fertile, metal-rich magmas that form ore deposits in the overlying crust.

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Section: Evidence Of Modal and Cryptic Volatile-rich Metasomatismsupporting

confidence: 84%

Highly siderophile elements mobility in the subcontinental lithospheric mantle beneath southern Patagonia

Tassara

Gonzáléz-Jiménez

Reich

et al. 2018

Lithos

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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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“…amphibole and/or phlogopite) during partial melting in the mantle source. Amphibole and phlogopite are indeed present in peridotite xenoliths hosted by these basalts (Aka et al 2004;Temdjim et al 2004;Teitchou et al . Since amphibole and phlogopite are not primary mantle minerals, they are believed to precipitate in the mantle from percolating metasomatising melts or fluids (Greenough 1988;Green and Wallace 1988;Hawkesworth et al 1990), and are restricted to the cold conductive mantle lithosphere because temperatures in the hot convective mantle are too high for their stability (Class and Goldstein 1997).…”

Section: Trace Element Evidencementioning

confidence: 99%

Depth of Melt Segregation Below the Nyos Maar-Diatreme Volcano (Cameroon, West Africa): Major-Trace Element Evidence and Their Bearing on the Origin of CO2 in Lake Nyos

Aka

2015

Advances in Volcanology

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The Nyos maar-diatreme volcano on the Oku Volcanic Group (OVG) in NW Cameroon carries yet the most infamous maar lake in the world because the lake exploded in 1986 releasing CO 2 that killed *1,750 people and over 3,000 livestock. A process of safely getting rid of accumulated gas from the lake started in 2001. Even though *33 % of it has been removed, gas continues to seep into the lake from the mantle, so the lake still poses a thread. Available data on basaltic lava from the maar-diatreme volcano and other volcanoes of the OVG are used here to determine the depth and location where the magmas are produced, and to make inferences on the generation of CO 2 in the Nyos mantle. Fractionation-corrected major element data agree well with experimental data on mantle peridotite and suggest that Lake Nyos magmas formed at pressures of 2-3 GPa in the garnet stability field. This inference is corroborated by trace element models that indicate small degree (1-2 %) partial melting in the presence of residual garnet (2-3 %). The basalts have elevated High Field Strength Element (HFSE) ratios (Zr/Hf = 48.5 ± 1.2 and Ti/Eu = 5,606 ± 224) which cannot be explained by any reasonable fractional crystallization model. A viable mechanism would be melting of a mantle that was previously spiked by percolating carbonatitic melts. It is suggested that small degree partial melting of this metasomatised mantle produces the lavas with super chondritic HFSE ratios, and is generating the CO 2 that seeps into and accumulates in the lake, and which asphyxiated people and animals during the 1986 gas disaster. This finding requires that current efforts to degas Lake

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Mineralogical and geochemical fingerprints of mantle metasomatism beneath Nyos volcano (Cameroon volcanic line)

Cited by 11 publications

References 0 publications

Highly siderophile elements mobility in the subcontinental lithospheric mantle beneath southern Patagonia

Highly siderophile elements mobility in the subcontinental lithospheric mantle beneath southern Patagonia

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

Depth of Melt Segregation Below the Nyos Maar-Diatreme Volcano (Cameroon, West Africa): Major-Trace Element Evidence and Their Bearing on the Origin of CO2 in Lake Nyos

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