The Bafoussam area in western Cameroon is part of the central Cameroon Volcanic Ligne(CVL).This study presents the mineralogy,major and trace element compo-sitions,Sr-Pb-Hf isotopes,and new K-Ar geochronological data about mafic and felsic volcanic rocks.These rocks belong to two different series:A transitional series made of basalts,basaltic andesite,and trachytes and an alkaline mafic series with basalts,hawaiites,and basanites.New age data show that the transitional series belongs to the oldest part of the CVL and was emplaced between 47 and 35 Ma.The alkaline volcanism is younger,with ages ranging from 10 to 4.5 Ma.Magmatic evolution in both series is accomplished through a fractional crystallization process,with the removal of olivine and clinopyroxene,while plagioclase does not seem to be a major crystallizing phase.All the samples are enriched in incompatible trace elements,but the rocks from the alkaline series have more fractionated REE patterns and high Nb content compared to the transitional mafic lavas.Alkaline lavas have lower initial 87Sr/86Sr and higher 176Hf/177Hf and Pb isotopic ratios than the transitional lavas.Low La/Nb and high 87Sr/86Sri ratio are among chemi-cal characteristics that show that some samples from the transitional series have interacted with a crustal component during their evolution in the crust.They cannot be used for discussing the mantle source of the volcanic rocks from this series.Trace elements show that primary magmas for both series formed in a garnet-bearing mantle source,with higher partial melting degrees(3-5％)for the transitional magmas than for the alkaline magmas(＜2.5％).Com-bining trace elements and isotopic ratios,we show that the Bafoussam lavas formed from two different mantle sour-ces.Transitional magmas formed from a pyroxenite-bear-ing enriched mantle with low Pb isotopic composition.This mantle source is present in all the oldest lavas from the CVL.Alkaline magmas formed from an HIMU-like mantle source,different from the Mt Cameroon HIMU mantle source.The depleted asthenospheric mantle is not involved in the Bafoussam magmatism and the two mantle sources are probably located in the lithospheric mantle,in agree-ment with recent geophysical models presenting the CVL as a consequence of the partial melting of the lithospheric mantle in response to edge convection along the margin of the Congo craton.

Philippe Essomba;Gilles Chazot;Nicaise Blaise Tchuimegnie Ngongang;Arnaud Agranier;Pierre Kamgang;Hervé Bellon;Philippe Nonnotte;Pierre Wotchoko;Innocent Badriyo

Département Des Sciences de La Terre,Faculté Des Sciences,Université de Yaoundé 1,B.P.812 Yaoundé,Cameroun;Geo-Ocean,CNRS,Ifremer,UMR6538,Univ Brest,29280 Plouzane,France;Département Des Sciences de La Terre,Faculté Des Sciences,Université de Douala,Douala,Cameroun;Department of Geology,Higher Teacher Training College,University of Bamenda,Bambili,Bamenda,Cameroon;Département de Séismologie et Géologie,Observatoire Volcanologique de Goma-RDC,Goma,République Démocratique du Congo

地球化学学报（英文版）

[1]Philippe Essomba;Gilles Chazot;Nicaise Blaise Tchuimegnie Ngongang;Arnaud Agranier;Pierre Kamgang;Hervé Bellon;Philippe Nonnotte;Pierre Wotchoko;Innocent Badriyo-.The Bafoussam volcanic series:origin and evolution of the volcanism along the Cameroon volcanic line)[J].地球化学学报（英文版）,2022(06):1049-1068

Bafoussam,Ligne,trachytes,hawaiites,basanites,crystallizing,86Sri,Transitional

volcanic,series,origin,evolution,volcanism,along,Cameroon,area,western,central,Volcanic,CVL,This,study,presents,mineralogy,major,trace,sitions,Pb,isotopes,new,Ar,geochronological,data,about,mafic,felsic,rocks,These,two,different,transitional,made,basalts,basaltic,andesite,alkaline,New,show,that,belongs,oldest,was,emplaced,between,younger,ages,ranging,from,Magmatic,both,accomplished,through,fractional,crystallization,process,removal,olivine,clinopyroxene,while,plagioclase,does,seem,phase,All,samples,enriched,incompatible,elements,but,have,more,fractionated,REE,patterns,Nb,content,compared,lavas,Alkaline,lower,initial,87Sr,higher,176Hf,177Hf,isotopic,ratios,than,Low,La,among,chemi,characteristics,some,interacted,crustal,component,during,their,They,cannot,used,discussing,mantle,this,Trace,primary,magmas,formed,garnet,bearing,partial,melting,degrees,Com,bining,pyroxenite,composition,HIMU,like,Mt,depleted,asthenospheric,involved,magmatism,sources,probably,located,lithospheric,agree,recent,geophysical,models,presenting,consequence,response,edge,convection,margin,Congo,craton

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