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
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.
