Geochemical and Sr‐Nd isotopic records of Paleoproterozoic metavolcanics and mafic intrusive rocks from the West African Craton: Evidence for petrogenesis and tectonic setting

Abstract

Metavolcanics and mafic intrusive rocks of the Paleoproterozoic Birimian terrane in the southeastern part of the West African Craton, Ghana, were analyzed for major and trace elements and Nd and Sr isotopic data to constrain the geodynamic evolution of the Birimian Supergroup. The metavolcanic rocks consist of metabasalts, meta‐andesites, and amphibolites, whereas the mafic intrusions are mainly gabbros, hornblendites, and dolerites. The rocks are tholeiitic in composition and show the classic features of arc magmatism. The metavolcanics display significant enrichments in large ion lithophile elements (LILE) and light rare earth elements, relative to high field strength elements (HFSE) and heavy rare earth elements. The multielement patterns of the rocks also show positive Pb, Ba, Th, and Sr and negative Nb, Ta, and Ce anomalies that are typical characteristics of subduction‐related magmas. They also have La/Nb ratios <3 and La/Ta ratios <43 that are similar to other Archean and Birimian greenstone belts in West Africa. The rocks have εNd (2.1 Ga) values of −0.96 to +2.60, and Nd model ages of 2.24–2.51 Ga (TDM1) and 2.16–2.45 Ga (TDM2), indicating their juvenile character with possible contributions from pre‐Birimian crustal materials in their sources. The εNd values suggest a depleted source and further indicate that they were probably produced in an almost entirely oceanic environment with minor influence from the continental crust. The Nd isotopic results are consistent with the island arc model, which views Paleoproterozoic terranes of the West African Craton in the context of subduction–accretion processes. Accordingly, these processes may have played a role in the formation of the Columbia supercontinent during the Paleoproterozoic (2.1–1.8 Ga) orogenic events.

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“…87 Sr/ 86 Sr sources from West Africa and Trans Mexican Volcanic Belt (TMVB) used for calibration. Compilation of 87 Sr/ 86 Sr from West Africa for groups A ( Liégeois et al, 1991 ), B ( Bernard-Griffiths et al, 1988 ), C ( Peucat et al, 2005 ), D ( Ferrière et al, 2010 ), E ( Fullgraf et al, 2013 ), and F ( Sakyi et al, 2018 ) while G ( Solís-Pichardo et al, 2017 ) correspond to the TMVB for isotopic comparison.…”

“…Mexican Volcanic Belt (TMVB) used for calibration. Compilation of 87 Sr/ 86 Sr from West Africa for groups A (Liégeois et al, 1991), B (Bernard-Griffiths et al, 1988, C (Peucat et al, 2005), D (Ferrière et al, 2010), E (Fullgraf et al, 2013), andF (Sakyi et al, 2018); while G (Solís-Pichardo et al, 2017) correspond to the TMVB for isotopic comparison. a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a Streptomyces niveus Sr concentration (ppm)…”

Geochemical constraints on provenance and source area weathering of metasedimentary rocks from the Paleoproterozoic (~2.1 Ga) Wa-Lawra Belt, southeastern margin of the West African Craton

“…volcanic rocks and associated granitoids) indicate that the Birimian constitutes a huge addition of materials from the mantle (e.g. Dampare et al, 2009;Sakyi et al, 2018Sakyi et al, , 2014 although the terrane may be underlain substantially by Archaean basement. In Ghana, the metasedimentary rocks in the Birimian Supergroup have received relatively less attention, even though they form the dominant component of the overall Birimian rocks.…”

Origin and tectonic significance of the metavolcanic rocks and mafic enclaves from the Palaeoproterozoic Birimian Terrane, SE West African Craton, Ghana

“…The tectonic settings proposed by some of the studies so far range from the generation of the Birimian juvenile crust in arc environments (e.g. Sylvester & Attoh, 1992;Asiedu et al 2004;Dampare et al 2005;Sakyi et al 2014Sakyi et al , 2018a to plume-related magmatism (e.g. Abouchami et al 1990;Lompo, 2009).…”