The Pan-African West Congo belt in the Republic of Congo (Congo Brazzaville): Stratigraphy of the Mayombe and West Congo Supergroups studied by detrital zircon geochronology

摘要

The African part of the Neoproterozoic Aracuai-West Congo orogen forms a more than 1400 km long belt, running from Gabon in the north to Angola in the south, parallel to the South Atlantic coast. It consists of the West Congo fold belt in the west and a largely undeformed sedimentary foreland basin in the east. In the Republic of Congo (Congo Brazzaville) these are known as, respectively, the 'Mayombe fold belt' and the 'Niari basin'. The 'Mayombe fold belt is largely made up of strongly deformed metasedimentary rocks of the Mayombe Supergroup and its reworked granitoid basement complex. The Niari basin comprises the sedimentary strata of the West Congo Supergroup, which contain a unit of diamictite and associated cap-carbonate, related to the Marinoan (ca. 635 Ma) glaciation. In this paper detrital zircon U-Pb data are employed to investigate the relationships between the Mayombe and West Congo Supergroups in Congo Brazzaville, as well as the relationships with similar stratigraphic units in the Democratic Republic of Congo (DR Congo). Unfortunately, major differences in stratigraphical nomenclature exist between Congo Brazzaville and DR Congo which, together with geological differences, complicate comparisons. The terminology used in this paper follows the Congo Brazzaville tradition.