Structural Evolution of a Precambrian Segment: Example of the Paleoproterozoic Formations of the Mako Belt (Eastern Senegal, West Africa)

Abstract

The western part of the Kedougou Kenieba Inlier is located in the West African Craton. It consists of paleoproterozoic NE-trending elongate belts (subprovinces) of metavolcanic and granitic rocks that alternate with metasedimentary belts. Major linear fault such as the MTZ which also approximate a north-easterly trend form the eastern boundaries. The field observations and geophysics analyses were completed by a microscopic study. Based on these data we define across this region four lithostructural domains from east to west. The western domain is structurally complex. The rocks of this domain have been subjected to a complex history of polyphase deformation and metamorphism. The structural analyse allow us to distinguished three deformation events. The deformation results in the formation of D1 thrust tectonic and D2 and D3 transcurrent tectonic. The structural evolution of the Mako Belt is characterized by deformation dominated by the intrusion of large TTG batholiths (D1) followed by basins formation and transpression accommodating oblique convergence and collision (D2 and D3). The change from thrusting (D1 deformation to transcurrent motion (D2 and D3) is recorded in the marginal basin of the central domain and in Tinkoto pull apart basin. The timing of these basins indicates a diachronous evolution. Deformation styles within the basin are compatible with a dextral transpression which terminated at ca 2090 Ma. Small extensional basins formed over the rocks of the Mako Belt are filled with continental detrital sedimentary rocks that show weak foliation and active felsic volcanism. We suggest that the sinistral transpressive tectonic associated with oblique subduction may have generated the pull-apart basin and subaqueous volcanism. In part these features are now related to terrain accretion, thrusting and strike slip movement during oblique convergence. The inversion of the large scale structural evolution from thrusting to strike slip is common to modern orogenies.

Polycyclic Evolution of Paleoproterozoïc Rocks in the Southwestern Part of the Mako Group (Eastern Senegal, West Africa)

“…In a second step, stress moved toward the NE-SW direction and made the resulting brittle structures arranged in NS dextral corridors. The idea of an early phase of tangential deformation has already been mentioned by Ledru et al, [13] and Diène et al, [20]. According to these authors this tangential phase is followed by two separate transcurrent tectonic events named D2 and D3.…”

New Approach of Structural Setting of Gold Deposits in Birimian Volcanic Belt in West African Craton: The Example of the Sabodala Gold Deposit, SE Senegal

“…The Eburnean tectonothermal event has been interpreted as occurring as a period of Birimian volcanic eruption, intrusion of granitoids and a period of metamorphism, uplift and erosion (2130 Ma -1980 Ma, Feybesse et al, [8]). Emplacement of sub-volcanic plutons such as occurred during the Eburnean tectono-thermal event around 2070 Ma (Gueye et al, [20] [21]; Hirdes and Davies, [22]; Diene et al, [23]) ago may have contributed to the formation of late, discordant epigenetic veins, vein systems and stockwerks in the Birimian. The lode gold deposits in the Birimian are concentrated along the contacts of the volcanic belts with the sedimentary basins.…”

Petrological and Structural Approach to Understanding the Mechanism of Formation and Development of Paleoproterozoic Calc-Alkaline Volcanic Rocks of West Africa’s Craton: An Example of the Mako and Foulde Groups (Kedougou Inlier in Western Senegal)

“…The geometric design of the spatial distribution of the major lithological units (Figure 7) suggests a synchronic relationship between tectonics and magmatism. The lithostructural evolution of the Mako Group reveals great lithotectonic units, notably various basins including marginal and pull-apart basins (Diene et al, [38]).…”

“…The structural evolution of the Mako Group is marked by two deformation phases that form a contunium: a tangential D1 phase that caused the crustal thickening and which is related to a horizontal shortening of the crust; this resulted in the formation of marginal basins; a D2-3 evolution characterized by transcurrent tectonics controlling the geometry and evolution of pull-apart basins (Diene et al, [38]). These two evolutions may create NE-SW, NS, EW and NW-SE-oriented overlapping and transcurrent structures affecting the whole aspect of the volcanic belt.…”

“…The study of the sedimentation and deformation inside the basins suggests that the D2-3 transcurrent phase has caused the development of these basins. The structural evolution of the Mako volcanic belt is characterized by deformations dominated by a D1 phase preceding the formation of basins and transpressive tectonics that includes an oblique convergence (Diene et al, [38]). The sedimentation in the various basins filled with continental calc-alkaline, volcano-sedimentary and detritic volcanic rocks, together with the distortions affecting these formations, could suggest that transpressive tectonics associated with oblique subduction may have caused the development of pull-apart basins and subaerial volcanism.…”