U-Pb and Ar-Ar geochronological constraints on timing of deformation and peak metamorphism in the Central Africa Orogenic Belt, Yaoundé Domain, Cameroon

Abstract

ABSTRACT The Central Africa Orogenic Belt (CAOB) and the Transaharan and Sergipano belts form a major West Gondwana suturing orogen affected by D1–D4 compressional deformation. Microstructural observations, mineral chemistry, zircon, and titanite laser ablation ICP-MS U-Pb dating, and biotite, muscovite, and K-feldspar 40Ar-39Ar age data are used to constrain the timing of rocks formation and D1–D4 events in the Yaoundé Domain of the CAOB, as well as characterize the Neoproterozoic-Cambrian transition. The Yaoundé Domain rocks were deposited on a pre-Neoproterozoic structure that was overprinted by a c. 1000–700 Ma mega arc/back-arc system and related Tonian to Ediacaran magmatism. Older U-Pb dates (1000 up to 2700 Ma) are inheritance from a pre-existing crust. The D1–D4 compressional events relate to the inversion of the c. 1000–700 Ma mega-rift system. New dates at c. 700 Ma, c. 630 Ma, c. 580–555 Ma constrain the timing of D1, D2, D3+D4, respectively. The peak of accompanying metamorphism occurred at 614 ± 4 Ma during D2. This was followed by a c. 115 Ma period of deformation-driven crustal exhumation and cooling that extended into the Cambrian. New data document short episodes of rapid denudation and cooling (up to 0.9 km/Ma and 40°C/Ma at c. 578 Ma in gneiss and up to 5 km/Ma and >125°C/Ma at c. 555 Ma in micaschist). It is proposed that the CAOB and correlative belts are parts of the orogenic hinterland formed from accretion and collision between the West African Craton and the Sahara Metacraton precursor. The correlated belts appear to represent the result of a protracted tectono-metamorphic and magmatic process that started in late Mesoproterozoic (c. 1167 Ma) and continued through the Neoproterozoic to the Cambrian (c. 500 Ma).