Lu-Hf Isotopic Data of the Mbé-Sassa-Mbersi Tonalite (Central Cameroon Domain): Indicator of ca. 1.0 Ga Juvenile Tonian Magmatism in the Region

Abstract

The Pan-African/Brasiliano orogenic belts are a part \nof numerous Neoproterozoic orogenic belts that belong to the long-lived orgenic \ncycle that distancing phase started at the Tonian around 1.0 Ga. The Tonian magmatism \nfairly documented in the Neoproterozoic belts of Borborema Province \n(NE-Brazil), seemed so far inexistent in the Central African Orogenic Belt \n(CAOB) although these two belts were geologically correlated. Through the Lu-Hf \ngeochronological analysis on zircon of tonalite, the present work, coupled with \nthe previous data, suggests the existence of a Tonian age magmatism in the \nCentral Cameroon Domain of the CAOB although the latter is much reworked. The \nNguesseck tonalite outcrops in the northern part of the Mbe-Sassa-Mbersi region, in the northern edge of Central \nCameroon Domain of the CAOB and in the Tchollire-Banyo shear zone (TBSZ). The Lu-Hf data obtain on \nthe zircon grains of this tonalite reveal juvenile HfTDM age of ca. \n1.0 Ga. This age, combined to the previous geochemical data suggests that the protholites of this tonalite would have \nextracted from the source during the distancing phase (rifting and \noceanization) of the Pan-african/Brasiliano orogeny at the early Neoproterozoic.