Structure and LA-ICP-MS zircon U-Pb dating of syntectonic plutons emplaced in the Pan-African Banyo-Tchollire shear zone (central north Cameroon)

摘要

The Tchollire massif, in central north Cameroon, consists of elongated granite plutons that crop out along the Pan-African Tchollire-Banyo shear zone (TBSZ), a potential suture zone within the Central Africa Orogenic Belt. New structural and geochronological data on these granites constrain the tectonic regime and timing of the TBSZ. The plutons consist of syntectonic granites and granodiorite containing dioritic mafic enclaves. They show an S2 sub-vertical foliation, that trends NE-SW to ENE-WSW. The related L-2 lineation is subhorizontal to shallowly plunging to the SW or NE. Kinematic indicators such as asymmetric folds, sigmoidal-shape boudins, shear bands, imbricated feldspar phenocrysts along antithetic fractures point to a sinistral sense of shear. Microstructural analysis shows that structures are acquired from the submagmatic to the low temperature solid state suggesting progressive deformation of the magma during its emplacement, crystallization and cooling. U-Pb zircon dating on this massif yields emplacement ages of 719 +/- 12 Ma for the biotite-amphibole granite and muscovite granite, 652.2 +/- 5.4 Ma for the biotite-granite and 632 +/- 13 Ma for the leucogranite. These geochronological data show in addition, Palaeoproterozoic inherited ages of 1631 +/- 30 Ma on the leucogranites of this massif, and point to a Palaeoproterozoic contribution in their genesis. The range of ages (ca. 87 Ma) points to the timing of syntectonic emplacement of felsic magmas coeval with sinistral transpression along the TBSZ during the Pan-African orogeny. These results show that the TBSZ has recorded prolonged deformation associated with crustal magmatism between the Palaeoproterozoic Adamawa-Yade domain to the southeast and the Sinassi-Mayo Kebbi Neoproterozoic magmatic arc to the Northwest. (C) 2017 Elsevier Ltd. All rights reserved.