The petrostructural characteristics and 207Pb/206Pb zircon data from the Ngomedzap-Akongo area (Nyong complex, SW-Cameroon)

Abstract

Herein, we constrain the Ngomedzap–Akongo geodynamic evolution in the eastern part of the Nyong complex (NyC) in SW Cameroon that belongs to the Paleoproterozoic West Central African Fold Belt (WCAF) through petrostructural field observations, laboratory analyses, and 207Pb/206Pb zircon geochronology. It consists of magnetite bearing quartzite, metagranodiorite, metaanorthosite, metagabbro, and metasyenites that have recorded a polyphase D1–D3 deformation. D1, likely a pure shear-type, has been strongly overprinted by the D2 transpression flow regime that emplaced the Nyong tectonic nappe, transported top – to the East onto the Congo shield. This nappe is dissected by D3 blastomylonitic shear-zones. Both the D2 and D3 have controlled the actual geometry of the Nyong belt, later crosscut by D4 multiple brittle tectonic styles, likely post-orogenic. Zircon geochronology yielded 207Pb/206Pb zircon geochronology protolith Archean mean ages of 2764 ± 26 Ma (MSWD = 0.81) in metagranodiorite; 2816 ± 34 Ma (MSWD = 1.3) and 2789 ± 13 Ma (MSWD = 0.28) in metasyenites. These new data corroborate old ones and, together, document the Archean origin of the NyC as details of the Nyong fold-and-thrust belts that of WCAFB and South American homologous due to the colliding Congo-San Francisco shields associated with Eburnean/Trans Amazonian orogeny (~2100–2050 Ma).