The Marinkas Quellen Carbonatite Complex, southern Namibia; carbonatite magmatism with an uncontaminated depleted mantle signature in a continental setting

The Marinkas Quellen Carbonatite Complex, in southern Namibia, forms part of the ca. 490–550 Ma Kuboos-Bremen Igneous Province, a zone of alkaline igneous rocks that intrude the Mesoproterzoic to Paleoproterozoic Namaqualand Metamorphic Province and Neoproterozoic platform sediments. The carbonatite complex includes Ca-rich, Mg-rich and Fe-rich carbonatites as well as late ferrocarbonatite dykes that show extreme enrichments in Mn, REE and Th. Compared to most carbonatites, those at Marinkas Quellen are generally depleted in most trace elements, particularly Ba and the LREE. These depletions are accompanied by what are possibly the highest ϵNd values (>+5.3) observed for carbonatites from a continental setting, and combined with low initial 87Sr/86Sr values (<∼0.7029), indicate a depleted asthenospheric source, similar to that associated with oceanic island basalts and carbonatites from oceanic settings. Such compositions suggest that old, metasomatized lithospheric mantle was not a significant component of sub-continental southern Namibia immediately after the Neoproterozoic closure of the Atlantic Ocean.