Anatexis of metadiorite from the Yaoundé area, Central African Orogenic Belt in Cameroon: implications on the genesis of in-source granodiorite leucosomes

This paper presents integrated whole-rock geochemistry, LA-ICP-MS zircon U–Pb geochronology, and zircon and monazite thermometry of the Yaounde in-source granodiorite leucosomes in order to better constrain the crustal growth of the Yaoundé segment of the Central African Orogenic Belt (CAOB). The Yaoundé area is dominantly made up of extensively melted metadiorites hosting partially digested enclaves of metasediments and in-source granodiorite leucosomes. Field investigations have revealed that the regional structure is dominated by the shallow-dipping to occasionally subvertical S n foliation characterized by variable trending resulting to the transposition of the locally E-W trending S n -1 foliation in metadiorite. New LA-ICP-MS zircon U–Pb geochronology indicates partial melting age crystallization at 595 ± 4 Ma for the in-source granodiorite leucosomes. This in the Yaoundé area is coeval with and emplacement of some syntectonic granitoids of the CAOB. Metadiorites are high-K calc-alkaline while granodiorite leucosomes are medium-K calc-alkaline and both rocks are magnesian, display LREE enrichment, and LILE depletion as well as strong depletion in Nb–Ta, Sr, P, and Ti. The protholith of the Yaoundé metadiorites derived from partial melting of mixed source involving a metasomatized mantle with the contribution of crustal materials. In-source granodiorite leucosomes derived from the partial melting of metadiorites during a period of intense migmatization in the Yaoundé group. The average T Zr T Ti-in-zr and T REE (ca. 794 °C, 767 °C, 821 °C, respectively) estimates of the melts are similar to estimated temperatures (ca. 750–800 °C) for the host metadiorites, suggesting that the melting took place in the deep crustal level as inferred by estimated pressure of 9–13 kbar.