Petrography and geochemical characterization of the Baibokoum syenitic pluton(Southern Chad):Implication for the magma genesis  

作　　者：Gustave Baissemia Ronang Merlin Gountie Dedzo Jules Tcheumenak Kouemo Moussa Ngarena Klamadji Diondoh Mbaguedje Maurice Kwekam 

机构地区：[1]Department of Earth Sciences,Faculty of Science,University of Maroua,Maroua,Cameroon [2]Département de Mines Et Génie Géologie,FacultéDes Sciences de La Vie Et de La Terre,Universitéde Pala,Pala,Chad [3]Department of Life and Earth Sciences,High Teachers’Training College,University of Maroua,Maroua,Cameroon [4]Department of Earth Sciences,Faculty of Science,University of Douala,Douala,Cameroon [5]Department of Geology,Faculty of Sciences and Techniques,University Adam Barka of Abeche,Abeche,Chad [6]Department of Geology,University of Dschang,Dschang,Cameroon

出　　处：《Acta Geochimica》2025年第2期420-439,共20页地球化学学报(英文)

摘　　要：The Baibokoum syenitic pluton(BSP),located in southern Chad,to the NE of the Adamawa-Yadédomain,is one of the few strongly potassic magmatic bodies in the southern part of the Central African Fold Belt(CAFB)in Chad.It has been previously studied petrologically,but its petrogenesis has remained poorly known.Petrographic and whole-rock geochemical data presented in this article highlight their magma genesis and geodynamic evolution.The BSP consists of medium-to coarse-grained syenites associated with minor microdiorites,which occur as syn-plutonic dikes and mafic microgranular enclaves(MME)coarse-and medium-grained syenites outcrop respectively to the core and the border of the BSP.The syenite displays high-K and alkaline to trans-alkaline affinity.Petrographic and geochemical data suggest that medium-to coarse-grained syenites are from single magma source that evolved and differentiated by fractional crystallization in a magma reservoir.REE profiles show enriched LREEs(La_(N)/Yb_(N)=6.19-45.55)while HREEs show an almost flat profile(Dy_(N)/Yb_(N)=1.0-2.23),and the La/Sm and Sm/Yb ratios have led to propose that the aforementioned rocks derived from the partial melting of a garnet-spinel-lherzolite mantle source.Negative Nb and Ta anomalies indicate that this mantle source was modified by the addition of subduction-related material.Th/Yb ratios associated with high Ba/La ratios indicate that enrichment of the source could be related to slab-derived fluids.The parental magma of the BSP was generated by partial melting of the metasomatized lithospheric mantle that was modified into arc-magmatism material in a subduction setting.Its emplacement took place in two successive stages:a static stage of fractional crystallization and crystal settling in a deep magma source and a dynamic stage in a shear deformation setting during which stratified magma rises towards the upper crust,with evolved syenite magma being emplaced first and diorite later.The emplacement of the BSP was probably controlled by the evolution of the Tc

关 键 词：Baibokoum Syenitic Pluton Adamawa-Yadé Magma genesis Southern Chad 

分 类 号：P58[天文地球—岩石学]