Older Guiana basement south of the Imataca Complex in Venezuela, and in Suriname

Abstract

Older basement rocks of the northeastern Guiana shield in South America underlie supracrustal sequences in Venezuela, Guyana, Suriname, and French Guiana. The supracrustal rocks are believed to be coeval and of early Proterozoic age and have been correlated with the upper and lower Birrimian rocks of West Africa. In West Africa the Birrimian sequence is underlain by basement rocks of the 2,700 m.y. B.P. Liberian event. These supracrustal rocks in both South America and West Africa are intruded by granites related to the Trans-Amazonian–Eburnean thermotectonic event. Rb-Sr and U-Pb isotopic age measurements of the basement rocks of the Pastora province, Venezuela, and the Bakhuis Mountains, Suriname, yield ages of 2,600 to 2,800 m.y. The isotopic ages of these rocks in South America reinforce correlation of this older basement with the Imataca province in Venezuela, and the 2,700 ± 100 m.y. old Liberian orogeny basement in West Africa. A unified pre-drift Precambrian stratigraphy extending throughout the entire West African–Guiana shield area is strongly suggested.