This paper investigates the geochemistry of bulk rock and infers the petrogenesis of ultramafic rocks in the Boali Precambrian terrane in Mbi Valley,in the North of the Central African Republic(CAR).The studied rocks comprise coarse primary olivine and orthopyroxene relics(dominant phase),magnesio-hornblende,magnetite,and antigorite.Whole-rock analysis indicates low SiO2(aver-age of 43.14 wt％)and high MgO(19.84-26.98 wt％)contents and their Mg number(Mg#)ranges from 74 to 82.They display high Ni(526-865 ppm),Cr(1500-3680 ppm)contents.AFM(Na2O-K2O)-FeO-MgO)and ACM(Al2O3-CaO-MgO)ternary diagrams have revealed that the studied samples correspond to arc-related ultramafic cumulates.Chondrite-normalized REE plots display an increasing trend from La to Sm(CeN/SmN:0.74-1.81),weak negative to no Eu(Eu/Eu*=0.72-1.05)and strong negative Ce(Ce/Ce*=0.33-0.98)anomalies.Primitive mantle normalized of multi-element diagrams exhibit LREE enrichment and large ion lithophile elements(LILE)relative to high field strength elements(HFSE),and notable negative anomalies in Nb.This suggests the gen-eration of the parent melt by slab dehydration and wedge melting processes.In addition,incompatible trace element composition and ratios assumed that the source magma had an enhanced mantle source associated with a prominent influence of continental crust.Metasomatism of mantle wedge by plate-dehydrated,LILE-rich fluids and the incorporation of sediments derived from subduction explain the enhancement of the source.Integrated major and trace element compositions jointly with the tectonic reconstruction of this region and LA-ICP-MS U-Pb data on zircon constrain the emplacement age at ca.2099 Ma in a continental margin arc setting involving subduction of an oceanic plate beneath the continental lithosphere,dehy-dration of the slab and mantle wedge melting.This result intimate that the remnants of Paleoproterozoic oceanic crust or subduction event and subsequent basins closure extended from the Congo craton in Cameroon to CAR and NE Brazil.

Evine Laure Njiosseu Tanko;Prince Emilien Danguene;Philomene Nga Essomba Tsoungui;Sylvestre Ganno;Jonas Didero Takodjou Wambo;Bertin Guy Takam Tchoupe;Gus Djibril Kouankap Nono;Timoleon Ngnotue;Boniface Kankeu;Jean Biandja;Jean Paul Nzenti

Department of Earth Sciences,University of Dschang,P.O.Box 67,Dschang,Cameroon;Department of Earth Sciences,University of Bangui,P.O.Box 908,Bangui,Central African Republic;Department of Mining Engineering and Mineral Processing,School of Mines and Petroleum Industries,University of Maroua,P.O.Box 08,Kaélé-Maroua,Cameroon;Department of Earth Sciences,University of Yaoundé I,P.O.Box 812,Yaoundé,Cameroon;Department of Geology,HTTC,University of Bamenda,P.O.Box 39,Bambili,Bamenda,Cameroon;Institute for Geological and Mining Researches(IGMR),P.O.Box 4110,Yaoundé,Cameroon

地球化学学报（英文版）

[1]Evine Laure Njiosseu Tanko;Prince Emilien Danguene;Philomene Nga Essomba Tsoungui;Sylvestre Ganno;Jonas Didero Takodjou Wambo;Bertin Guy Takam Tchoupe;Gus Djibril Kouankap Nono;Timoleon Ngnotue;Boniface Kankeu;Jean Biandja;Jean Paul Nzenti-.Geochemistry and zircon U-Pb ages of the Paleoproterozoic ultramafic rocks of the Mbi Valley,Boali area,Central African Republic)[J].地球化学学报（英文版）,2022(03):515-535

Mbi,Boali,magnesio,antigorite,cumulates,Chondrite,Metasomatism,dration

Geochemistry,zircon,Pb,ages,Paleoproterozoic,ultramafic,rocks,Valley,area,Central,African,Republic,This,paper,investigates,geochemistry,bulk,infers,petrogenesis,Precambrian,terrane,North,CAR,studied,comprise,coarse,primary,olivine,orthopyroxene,relics,dominant,phase,hornblende,magnetite,Whole,analysis,indicates,low,SiO2,aver,wt,high,MgO,contents,their,number,Mg#,ranges,from,They,display,ppm,AFM,Na2O,K2O,FeO,ACM,Al2O3,CaO,ternary,diagrams,have,revealed,that,samples,correspond,arc,related,normalized,plots,increasing,trend,La,CeN,SmN,weak,negative,Eu,strong,anomalies,Primitive,mantle,multi,exhibit,LREE,enrichment,large,lithophile,elements,LILE,relative,field,strength,HFSE,notable,Nb,suggests,eration,parent,by,slab,dehydration,wedge,melting,processes,addition,incompatible,trace,ratios,assumed,source,magma,had,enhanced,associated,prominent,influence,continental,crust,plate,dehydrated,fluids,incorporation,sediments,derived,subduction,explain,enhancement,Integrated,major,compositions,jointly,tectonic,reconstruction,this,region,LA,ICP,data,constrain,emplacement,Ma,margin,setting,involving,oceanic,beneath,lithosphere,result,intimate,remnants,event,subsequent,basins,closure,extended,Congo,craton,Cameroon,NE,Brazil

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