Abstract
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 structures 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°C to 811°C and 658°C to 768°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 the magmatic-arc setting.
Highlights
Pan-African orogeny contributed to the formation and recycling of continental crust during the melting of Gondwana from 870 to 550 Ma ([1] [2])
In Cameroon, the Ngazi-Tina region belongs to the Adamawa-Yade domain of the Pan-African Central African Fold Belt (CAFB)
Fifty-five spots were obtained on zircon grains, including 29 for quartz monzonites and 26 for nepheline syenites
Summary
Pan-African orogeny contributed to the formation and recycling of continental crust during the melting of Gondwana from 870 to 550 Ma ([1] [2]). This Pan-African orogeny generated granitoids with different chemical compositions and evolutionary processes, in various tectonic environments [3]. During the past two decades, these granitoids have been studied in order to better understand the geodynamic evolution of this orogenic belt, which generally involve collision processes between continents ([7]-[12]) except recent works ([13] [14]), these studies do not integrate the trace element composition of zircon as well as the temperatures of the magma in which these zircons were crystallized. We examine the morphology, internal structure, trace elements and Ti-inzircon thermometer of zircon grains extracted from Ngazi-Tina rocks with the aim to clarify the origin and nature of magma, and to better constraint the tectonic setting
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