Anorogenic plutonism in the West Congo Belt of the Democratic Republic of Congo further supports early Tonian continental rifting in the Congo – São Francisco palaeocontinent

Abstract

Our paper presents an updated geological map and simplified lithostratigraphy of the West Congo Belt (WCB) in the Democratic Republic of Congo. The WCB holds a key position for understanding the construction of Gondwana and constitutes a larger orogenic system along with its Brazilian counterpart (i.e. Araçuaí orogen). Our current contribution focuses on a newly found and mapped early Tonian small-sized (6 × 4 km) plutonic body (so-called “Shinkakasa intrusive complex”) located in the westernmost amphibolite facies tectono-metamorphic domain of the West Congo fold-and-thrust belt. The complex is hosted by the Kimeza gneissic basement. Our fieldwork, samples and a new geological map provide a solid and updated geological background for more in-depth future work and proves essential for reinterpreting the broader tectonic framework. Our findings show that the Shinkakasa complex comprises felsic, intermediate and mafic to ultramafic rocks displaying mixing-mingling features and well-preserved igneous textures with only limited Panafrican metamorphic and tectonic overprint. According to previously published zircon U–Pb (SHRIMP) data, the Shinkakasa magmatism lasted from 911 Ma to 869 Ma and the complex was hosted by the 2069 Ma Kimeza gneissic basement.We compare the Shinkakasa complex with other small-sized intrusive complexes of the WCB, emplaced in a similar geological setting, such as the contemporaneous Mayumba bimodal complex of southwestern Gabon. This comparison is extended across the Atlantic Ocean to the recently studied early Tonian Salto da Divisa complex of southeastern Brazil. In the African counterpart we correlate the plutonic complexes to the early Tonian eastward arcuate (sub)volcanic bimodal successions (Seke-Banza Group of the DRC) largely exposed along trend of the orogen over a length of ca. 550 km in the greenschist facies domain of the WCB. Finally, we give an updated account of the early Tonian emplacement ages and lithostratigraphic terminology of the multiple bodies constituting this arcuate structure. Our data show that i) the vast majority of the anorogenic magmatism testifying for the aborted early Tonian continental rifting of the Congo - Sao Francisco palaeocontinent is exposed in the African counterpart, and ii) the extent of the (sub)volcanic successions largely predominates compared to the small-sized intrusive bodies such as the Shinkakasa complex.