Fig. 6

δ13C values (‰, VPDB) of hydrothermal calcites from the Ongeluk Formation. For comparison, data from modern unsedimented ridge-derived mid-ocean ridge (MOR) crusts (Gillis and Coogan 2011), sedimented ridge-derived MOR crusts (Coggon et al. 2004), rift-zone seafloor basalts (Gieskes et al. 1982), rift lake basement volcanics (Fouillac et al. 1989), and hydrothermal chimney (Dekov et al. 2014) from Afar Rift, Archean MOR basalts (Nakamura and Kato 2004; Shibuya et al. 2012), and rift-zone seafloor basalts (Shibuya et al. 2013a) are also shown