This paper discusses the deformation pattern of the Murchison Greenstone Belt, which is located in the northeastern Kaapvaal Craton, South Africa. The belt strikes northeast to southwest, is surrounded by gneisses and granitoids, and contains Meso-Archaean metavolcanics and metasediments. It is narrow, strongly deformed, and deeply rooted in the centre with a bulk keel geometry. Regional fabrics consist of a sub-vertical foliation at a low angle to the belt strike and bears steeply plunging lineations. From available data and our observations, we constructed a map of the foliation trajectories. The map reveals the following: the deformations are distributed, both the belt and the northern bounding gneisses are deformed together in a ductile way, and the plutons were emplaced during regional deformation. The overall structural pattern, together with the existence of contemporaneous intrusive and extrusive rocks outcropping at the surface, supports a vertical tectonic model, with burial of the upper crustal rocks within the underlying weak material during horizontal crustal shortening. The occurrence of leucogranite intrusions is consistent with the melting of buried sediments belonging to the belt at depth. Finally, ages available on syn-kinematic granitoids (2.97 to 2.77 Ga) suggest a long-lasting tectonic process.

S-type granites correspond to reworking of pre-existing continental material and form by partial melting of (meta)sediments. Early-to-mid Archaean S-type granites are rare and are more frequently found, usually as relatively small intrusions, during the Neoarchaean and the Archaean-Proterozoic transition. In the context of Archaean geology, their paucity is therefore significant, in that it matches the uncommon nature of processes during this period. In this study, we focus on the Late Mesoarchaean Willie pluton and Neoarchaean Lekkersmaak pluton, which crop out to the south of the Murchison Greenstone Belt in the Northern Kaapvaal Craton, South Africa. These intrusions represent the oldest S-type plutons known so far in the region. We constrain their petrogenesis by documenting their petrology, mineralogy (mineral composition), geochemistry (major and trace elements, Sr, Nd and O isotopes) and zircon U-Pb geochronology. The large Lekkersmaak and smaller Willie plutons represent two granites sharing many geochemical characteristics; they are both peraluminous, Ms-bearing S-type granites although they are more sodic and less potassic than typical S-type granites. The Willie granite was emplaced 2 816 ± 9 Ma ago while the Lekkersmaak yielded an emplacement age of 2 771 ± 2 Ma. Therefore, S-Type magmatism in the area occurred twice at 2.82 Ga and then 40 Myr later at 2.77 Ga, involving comparable immature metasedimentary sources and conditions of partial melting. Finally, a sample from the Lekkersmaak pluton devoid of S-type features as it is muscovite-free and aluminum poor was emplaced 2 734 ± 11 Ma ago. This confirms the episodic nature of magmatic activity south of the Murchison Greenstone Belt.

In the homogeneously deformed Murchison Greenstone Belt region, fluids circulations were focused along a localized deformation brittle-ductile zone, and the so-called Antimony Line. In order to trace the origin of the fluid, its composition, the temperature of the precipitation along the Antimony Line, we investigate the stable isotope (oxygen and carbon) and fluid inclusion compositions of the quartz-carbonate veins, as well as chemical analyses of the carbonates and ⁴⁰Ar-³⁹Ar dating on the fuchsite associated with the veins.