Geochronology of mafic and felsic rocks at the Mundonguara Mine: Insights into the chronostratigraphy of Archean greenstones within the Zimbabwe Craton

Abstract

The Zimbabwe Craton comprises a typical Archean TTG (tonalite-trondhjemite-granodiorite)-greenstone terrain. In this study we contribute with geochronological results from the Manica Greenstone Belt in Mozambique. The Manica Group constitutes the eastern extension of the Odzi-Mutare-Manica Greenstone Belt and comprises the Macequece Formation dominated by komatiitic rocks in its lower part and the sedimentary dominated M'Beza-Vengo Formation on top. U–Pb zircon data from this study yield crystallization ages between ca. 2.91 and ca. 2.94 Ga, reflecting two distinct magmatic episodes: (1) the intrusion of mafic dykes and granitoids into older komatiitic rocks, and (2) the emplacement of a rhyolitic volcanic unit within the Macequece Formation. These results indicate that the upper, more evolved mafic to felsic units of the formation were formed over a relatively short time interval during the late Archean. In contrast, the underlying komatiitic sequences currently lack precise age constraints. Overall, the data suggests that a major magmatic phase occurred around ca. 2.93 Ga, representing a significant stage in the development of the Macequece Formation. Based on these ages the Macequece Formation belongs to the 3.0–2.8 Ga Lower Greenstones of the Bulawayan Supergroup. However, similar ca. 2.9 Ga greenstone units are rare within the Zimbabwe Craton and in most cases lack significant amounts of komatiite rocks. A major unconformity is indicated by a ca. 170 Ma time gap between the Macequece Formation and the overlying M'Beza-Vengo Formation, suggesting the absence of stratigraphy intervals common in other greenstone belts within the Bulawayan Supergroup. The lower intercept ages between ca. 578 and ca. 856 Ma indicated that the Manica Group and surrounding TTG basement were affected by Neoproterozoic tectono-thermal events. The age of ca. 578 Ma is consistent with overprinting related to the Pan-African orogeny, while the older ages of 704–846 Ma coincide with bimodal magmatism associated with the Rodinia breakup. In particular, they also correlate well with the newly recognized 724–712 Ma Mutare-Fingeren Large Igneous Province, which affected the eastern Kalahari Craton.