The Kibaran cycle in Angola - a discussion

Three sedimentary formations of Kibaran age have been identified in SW Angola: the Cahama‐Otchinjau Formation, the Chela Group and the Leba‐Tchamalindi Formation. The Cahama‐Otchinjau Formation is intruded by red granites which are also found as boulders within the Chela Group basal conglomerate. These granites yielded the following Rb‐Sr ages: Matala region t = 1350 ± 65 Ma, 87Sr/86Sri = 0.716 ± 0.003; Ompupa region t = 1407 ± 26 Ma, 87Sr/86Sri = 0.7058 ± 0.0020; Otchinjau region t = 1411 ± 24 Ma, 87Sr/86Sri = 0.7052 ± 0.0012; Chitado region t = 1302 ± 20 Ma, 87Sr/86Sri = 0.7075 ± 0.0016. The red granites are cut by basic dykes of different compositions and ages. The noritic dolerites which are intrusive in the Chela Group yielded a good Rb‐Sr isochron at t = 1119 ± 27 Ma, 87Sr/86Sri = 0.7044 ± 0.0010. This age postdates the deposition of the Chela Group and of the Leba Tchamalindi Formation. These formations of Kibaran age extend to Namibia where they outcrop near the border. Their extension to the central and northeastern Angola is not yet well defined. Regarding the centralwestern region some metasediments outcrops are considered by several authors to belong to the Bale Group of Eburnean age or to the Oendolongo (s.s.) Group. It is assumed in this paper that some of the referred metasediments outcrops belong to the Bale Group while the others belong to the Oendolongo (s.s.) Group to which we suggest a Kibaran age. Concerning the eastern region we admit that the metasediments belonging to the Malombe and Luana Groups which are intruded by basic and granitoid rocks may be of Kibaran age. A more accurate establishment of the stratigraphy of this area will only be possible after isotope determinations, mainly on the basic rocks to define whether they belong to one or other of the two thermotectonic events already detected in Zaire at 2000–2220 Ma and 991 ± 30 Ma.