{"title":"乍得南部Baïbokoum正长岩体的岩石学和地球化学特征：岩浆成因意义","authors":"Gustave Baïssemia Ronang, Merlin Gountié Dedzo, Jules Tcheumenak Kouémo, Moussa Ngarena Klamadji, Diondoh Mbaguedjé, Maurice Kwékam","doi":"10.1007/s11631-024-00733-y","DOIUrl":null,"url":null,"abstract":"<div><p>The Baïbokoum syenitic pluton (BSP), located in southern Chad, to the NE of the Adamawa-Yadé domain, 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<sub>N</sub>/Yb<sub>N</sub> = 6.19–45.55) while HREEs show an almost flat profile (Dy<sub>N</sub>/Yb<sub>N</sub> = 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 Tcholliré-Banyo Fault and M'Béré Shear Zone during the Pan-African orogeny.</p></div>","PeriodicalId":7151,"journal":{"name":"Acta Geochimica","volume":"44 2","pages":"420 - 439"},"PeriodicalIF":1.4000,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Petrography and geochemical characterization of the Baïbokoum syenitic pluton (Southern Chad): Implication for the magma genesis\",\"authors\":\"Gustave Baïssemia Ronang, Merlin Gountié Dedzo, Jules Tcheumenak Kouémo, Moussa Ngarena Klamadji, Diondoh Mbaguedjé, Maurice Kwékam\",\"doi\":\"10.1007/s11631-024-00733-y\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>The Baïbokoum syenitic pluton (BSP), located in southern Chad, to the NE of the Adamawa-Yadé domain, 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<sub>N</sub>/Yb<sub>N</sub> = 6.19–45.55) while HREEs show an almost flat profile (Dy<sub>N</sub>/Yb<sub>N</sub> = 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 Tcholliré-Banyo Fault and M'Béré Shear Zone during the Pan-African orogeny.</p></div>\",\"PeriodicalId\":7151,\"journal\":{\"name\":\"Acta Geochimica\",\"volume\":\"44 2\",\"pages\":\"420 - 439\"},\"PeriodicalIF\":1.4000,\"publicationDate\":\"2024-09-09\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Acta Geochimica\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://link.springer.com/article/10.1007/s11631-024-00733-y\",\"RegionNum\":4,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q3\",\"JCRName\":\"GEOCHEMISTRY & GEOPHYSICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Acta Geochimica","FirstCategoryId":"89","ListUrlMain":"https://link.springer.com/article/10.1007/s11631-024-00733-y","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
Petrography and geochemical characterization of the Baïbokoum syenitic pluton (Southern Chad): Implication for the magma genesis
The Baïbokoum syenitic pluton (BSP), located in southern Chad, to the NE of the Adamawa-Yadé domain, 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 (LaN/YbN = 6.19–45.55) while HREEs show an almost flat profile (DyN/YbN = 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 Tcholliré-Banyo Fault and M'Béré Shear Zone during the Pan-African orogeny.
期刊介绍：
Acta Geochimica serves as the international forum for essential research on geochemistry, the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth‘s crust, its oceans and the entire Solar System, as well as a number of processes including mantle convection, the formation of planets and the origins of granite and basalt. The journal focuses on, but is not limited to the following aspects:
• Cosmochemistry
• Mantle Geochemistry
• Ore-deposit Geochemistry
• Organic Geochemistry
• Environmental Geochemistry
• Computational Geochemistry
• Isotope Geochemistry
• NanoGeochemistry
All research articles published in this journal have undergone rigorous peer review. In addition to original research articles, Acta Geochimica publishes reviews and short communications, aiming to rapidly disseminate the research results of timely interest, and comprehensive reviews of emerging topics in all the areas of geochemistry.
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