The geological structure, tectonics and geodynamic evolution of the territory of the Central African Republic

Abstract

Introduction: The key to decoding the Neoproterozoic structure of the Central African fold belt is the sector that territorially belongs to the Central African Republic. This sector takes up to 20% of the area of the belt. The structure of the territory of the Central African Republic is determined by a long and diverse history of its development. Moreover, at various stages, different geodynamic styles were quite clearly manifested. These styles determine the formation of the main structural and compositional complexes (SCCs) and, as a result, the minerageny. The purpose of the paper is to use published data and available materials of regional studies to create a working geodynamic model which will be used for solving regional cartographic problems and mineragenetic mapping.

Methods: The study was conducted using the method of geodynamic modelling, which involved a comprehensive analysis of stratified and unstratified SCCs, their compositions and age characteristics.

Results and discussion: The territory of the Central African Republic has four structural stages, Archean, Paleoproterozoic (Eburnean), Neoproterozoic (Pan-African), and Phanerozoic. The three lower stages have substages separated by internal unconformities. Each substage correlates with the corresponding orogenic phases and subsequent intraplate regimes. In modern coordinates, the northern and southern zones are distinguished, in which the dominant mechanism was Meso-Cenozoic rifting and Proterozoic thrusting. The Archean autochthonous stage is composed of TTG rocks (3.45 – 2.45 GA) associated with green-stone belts. The Paleoproterozoic stage forms the Parautochton Yangana, represented by green-stone-altered metabasalts, metapelites, and banded iron formations intruded by 2080 MA granitoids. The Neoproterozoic allochtonous stage is formed in the form of the Gbaya nappe composed of 640 – 650 MA granulites, charnokites, orthogneisses, and migmatites. Chaotic complexes in the northern framing of the Congo paleokraton belong to a special type of SCCs of the Neoproterozoic stage. The Phanerozoic stage is composed mainly of Cenozoic sediments in the northern part of the country and two large troughs in its south-western and north-eastern parts.

Intrusive magmatism is extremely diverse and is present in all structural stages, from the Archean to the Phanerozoic. There is an evolution of granitoid magmatism from TTG rocks characteristic of the Archean to the S-type in the Paleo- and, especially, the Neoproterozoic and to the A-type (Mesoproterozoic and Phanerozoic). The magmatites of the main composition of the Archean cycle were completely transformed into amphibolites. Basaltoids of the Paleo-, Meso-, and Neoproterozoic formed in both intraplate continental and oceanic structures. The latter show signs of allochthonous occurrence.

Based on the tectonic structure and material features of the dominant SCCs, which make up the Autochthon, Para-autochthon, Allochthon of the Precambrian and Phanerozoic cover of the territory of the Central African Republic, we traced the evolution of geodynamic processes and proposed a pilot geodynamic formation model. The evolution as a whole involves changing of plume processes that determine the compo

sition of the granite-green-stone regions of the Mesoarchean and Neoarchean to confidently recognisable mechanisms of plate tectonic generation in the Paleo and Neoproterozoic and intraplate manifestations of “hot spots” type and continental rifting in the Phanerozoic.

Conclusions: The case of the Central African Republic allows us to state that, regardless of the style of tectonic generation, the culminating orogenic phase is followed by a platform (paraplatform) stage of development characterised by relatively calm conditions, the formation of weathering crusts, and the accumulation of highly differentiated material. Paraplatform regimes were manifested in the Neoarchaean and Paleoproterozoic (Eburnean) times in the form of intraplate magmatism (trap formation and A-type granitoids). The main mechanism for the formation of structures in the Paleo- and Neoproterozoic was the collisional mechanism expressed in the active margin – ocean – passive margin system, the large-amplitude nappes within which belong to the territory of the Central African Republic and which at that time were a passive margin.