The Baïbokoum-Touboro-Ngaoundaye area is located in the Adamoua-Yade domain of the Pan-African Fold Belt in Central Africa. The present work concerns the petrographic and geochemical study. The study area is ...The Baïbokoum-Touboro-Ngaoundaye area is located in the Adamoua-Yade domain of the Pan-African Fold Belt in Central Africa. The present work concerns the petrographic and geochemical study. The study area is made up of plutonic rocks including two amphibole granites, four biotite and muscovite granites, two syenites and one monzonite sample. These rocks have a granular porphyroid texture, with a mylonitic tendency. The primary paragenesis consists of Opx + Cpx + Amp + Bt + Pl + Or + Mic + Qtz + Ap + Sph + Zr and the secondary paragenesis consisting of Ch + Op. Plutonic rocks are shoshonitic to calc-alkaline with a strong potassic affinity. The REE profiles of these rocks show a negative anomaly of Eu in the granites and no Eu anomaly in syenites and monzonite (syeno-diorite). Multielement spectra of plutonic rocks present a negative anomaly in Nb-Ta and Ti. Fractional crystallization is the process that made these rocks of study area. These rocks are placed in a subduction to syn-collisional (VAG + Syn-COLG) and of intraplate granitoids (WPG) environment.展开更多
The border of Cameroon and Chad is characterized by a Precambrian basement straddling the Touboro-Ba?bokoum area;this basement is made up of gneiss, amphibolite and granitoids (granite, syenite, granodiorite). The stu...The border of Cameroon and Chad is characterized by a Precambrian basement straddling the Touboro-Ba?bokoum area;this basement is made up of gneiss, amphibolite and granitoids (granite, syenite, granodiorite). The studied rocks display high-K calk-alcalcaline to shoshonitic characteristic. Granitoids are metaluminous. Rocks under study derived from partial melts from metabasaltic to metatonalitic sources, and partial melts from metagreywackes. They shear the same origin as many granitoids describe westward in the Meiganga area and west Cameroon. This shows that the basement straddling the Touboro-Ba?bokoum area belongs to the Adamawa-Yadé Domain of the Central African Fold Belt.展开更多
In Cameroon, the Ngazi-Tina region belongs to the Adamawa-Yade domain of the Pan-African Central African Fold Belt (CAFB). It is composed of two petrographic types: quartz-monzonites (majority) and nepheline syenites....In Cameroon, the Ngazi-Tina region belongs to the Adamawa-Yade domain of the Pan-African Central African Fold Belt (CAFB). It is composed of two petrographic types: quartz-monzonites (majority) and nepheline syenites. Two morphological types, prismatic and pyramidal, were recognized in the zircon grains samples. These zircon types display internal structure</span><span style="font-family:Verdana;">s</span><span style="font-family:""><span style="font-family:Verdana;"> typical of magmatic zircons. Zircons separated from the Ngazi-Tina samples contain higher abundances of Hf (close to 8000 ppm) and moderate trace elements (Y, Th, U, Nb, Ta) and REE contents, suggesting a variable degree of magmatic evolution. The chondrite-normalized REE patterns of zircons are characterized by LREE depletion relative to HREE with positive Ce and negative Eu anomalies, typical of magmatic zircons. The high Hf content together with high Ce/Ce*, Th/U, Zr/Hf ratios suggest magma crystallization under variable oxidation and oxygen fugacity. The application of Ti-in-zircon thermometer reveals crystallization temperatures ranging from 678</span><span style="color:#4F4F4F;font-family:Verdana;">°</span><span style="font-family:Verdana;">C to 811</span><span style="color:#4F4F4F;font-family:Verdana;">°</span><span style="font-family:Verdana;">C and 658</span><span style="color:#4F4F4F;font-family:Verdana;">°</span><span style="font-family:Verdana;">C to 768</span><span style="color:#4F4F4F;font-family:Verdana;">°</span><span style="font-family:Verdana;"></span><span style="font-family:Verdana;">C for quartz monzonites and nepheline syenites respectively. These features indicate probably a partial melting of continental crust as the source of these zircons grains and emplacement in</span></span><span style="font-family:Verdana;"> the</span><span style="font-family:Verdana;"> magmatic-arc setting.展开更多
The amphibole biotite gneiss (ABGn) in the Méiganga area forms part of a meta volcano-sedimentary sequence of the Adamawa Yade domain (AYD), Central African Fold Belt (CAFB). This sequence shows affinity with imm...The amphibole biotite gneiss (ABGn) in the Méiganga area forms part of a meta volcano-sedimentary sequence of the Adamawa Yade domain (AYD), Central African Fold Belt (CAFB). This sequence shows affinity with immature sediments (greywackes, arkoses) with intercalation of mafic lavas or tuffs. New 207Pb/206Pb zircon evaporation ages for two ABGn samples range from 1887 - 2339 Ma and from 675 - 889 Ma, respectively. These ages and evidence from internal zircon structures indicate that igneous rocks of Archean to Paleoproterozoic and of early Neoproterozoic age contributed to the detritus of the sedimentary sequence. The deposition of detritus took place prior to 614 - 619 Ma which represent the syntectonic emplacement of the Méiganga metadiorite. Leucogranites north to the Méiganga area were generated by melting of crust identical to that which provided the source of the ABGn. The metasedimentary sequence investigated in this study is similar to that of the southern part of the AYD and in the Borborema Province, NE Brazil. The tectonic and geochronologic characteristics of the AYD in the Méiganga area support the idea that during the Proterozoic, Central Africa and NE Brazil were part of the same continental landmass.展开更多
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 Ch...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 Tcholliré-Banyo Fault and M'BéréShear Zone during the Pan-African orogeny.展开更多
文摘The Baïbokoum-Touboro-Ngaoundaye area is located in the Adamoua-Yade domain of the Pan-African Fold Belt in Central Africa. The present work concerns the petrographic and geochemical study. The study area is made up of plutonic rocks including two amphibole granites, four biotite and muscovite granites, two syenites and one monzonite sample. These rocks have a granular porphyroid texture, with a mylonitic tendency. The primary paragenesis consists of Opx + Cpx + Amp + Bt + Pl + Or + Mic + Qtz + Ap + Sph + Zr and the secondary paragenesis consisting of Ch + Op. Plutonic rocks are shoshonitic to calc-alkaline with a strong potassic affinity. The REE profiles of these rocks show a negative anomaly of Eu in the granites and no Eu anomaly in syenites and monzonite (syeno-diorite). Multielement spectra of plutonic rocks present a negative anomaly in Nb-Ta and Ti. Fractional crystallization is the process that made these rocks of study area. These rocks are placed in a subduction to syn-collisional (VAG + Syn-COLG) and of intraplate granitoids (WPG) environment.
文摘The border of Cameroon and Chad is characterized by a Precambrian basement straddling the Touboro-Ba?bokoum area;this basement is made up of gneiss, amphibolite and granitoids (granite, syenite, granodiorite). The studied rocks display high-K calk-alcalcaline to shoshonitic characteristic. Granitoids are metaluminous. Rocks under study derived from partial melts from metabasaltic to metatonalitic sources, and partial melts from metagreywackes. They shear the same origin as many granitoids describe westward in the Meiganga area and west Cameroon. This shows that the basement straddling the Touboro-Ba?bokoum area belongs to the Adamawa-Yadé Domain of the Central African Fold Belt.
文摘In Cameroon, the Ngazi-Tina region belongs to the Adamawa-Yade domain of the Pan-African Central African Fold Belt (CAFB). It is composed of two petrographic types: quartz-monzonites (majority) and nepheline syenites. Two morphological types, prismatic and pyramidal, were recognized in the zircon grains samples. These zircon types display internal structure</span><span style="font-family:Verdana;">s</span><span style="font-family:""><span style="font-family:Verdana;"> typical of magmatic zircons. Zircons separated from the Ngazi-Tina samples contain higher abundances of Hf (close to 8000 ppm) and moderate trace elements (Y, Th, U, Nb, Ta) and REE contents, suggesting a variable degree of magmatic evolution. The chondrite-normalized REE patterns of zircons are characterized by LREE depletion relative to HREE with positive Ce and negative Eu anomalies, typical of magmatic zircons. The high Hf content together with high Ce/Ce*, Th/U, Zr/Hf ratios suggest magma crystallization under variable oxidation and oxygen fugacity. The application of Ti-in-zircon thermometer reveals crystallization temperatures ranging from 678</span><span style="color:#4F4F4F;font-family:Verdana;">°</span><span style="font-family:Verdana;">C to 811</span><span style="color:#4F4F4F;font-family:Verdana;">°</span><span style="font-family:Verdana;">C and 658</span><span style="color:#4F4F4F;font-family:Verdana;">°</span><span style="font-family:Verdana;">C to 768</span><span style="color:#4F4F4F;font-family:Verdana;">°</span><span style="font-family:Verdana;"></span><span style="font-family:Verdana;">C for quartz monzonites and nepheline syenites respectively. These features indicate probably a partial melting of continental crust as the source of these zircons grains and emplacement in</span></span><span style="font-family:Verdana;"> the</span><span style="font-family:Verdana;"> magmatic-arc setting.
文摘The amphibole biotite gneiss (ABGn) in the Méiganga area forms part of a meta volcano-sedimentary sequence of the Adamawa Yade domain (AYD), Central African Fold Belt (CAFB). This sequence shows affinity with immature sediments (greywackes, arkoses) with intercalation of mafic lavas or tuffs. New 207Pb/206Pb zircon evaporation ages for two ABGn samples range from 1887 - 2339 Ma and from 675 - 889 Ma, respectively. These ages and evidence from internal zircon structures indicate that igneous rocks of Archean to Paleoproterozoic and of early Neoproterozoic age contributed to the detritus of the sedimentary sequence. The deposition of detritus took place prior to 614 - 619 Ma which represent the syntectonic emplacement of the Méiganga metadiorite. Leucogranites north to the Méiganga area were generated by melting of crust identical to that which provided the source of the ABGn. The metasedimentary sequence investigated in this study is similar to that of the southern part of the AYD and in the Borborema Province, NE Brazil. The tectonic and geochronologic characteristics of the AYD in the Méiganga area support the idea that during the Proterozoic, Central Africa and NE Brazil were part of the same continental landmass.
文摘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 Tcholliré-Banyo Fault and M'BéréShear Zone during the Pan-African orogeny.
