Intracontinental anorogenic alkaline magmatism and carbonatites, associated mineral systems and the mantle plume connection

Intracontinental alkaline complexes and carbonatites commonly occur in rift-related settings, best exemplified by the Cenozoic-present day East African Rift System. Examples in the ancient geological record are more difficult to unravel due to subsequent overprinting during tectono-thermal events unrelated to the original rifting. In the present paper, with the exception of the Bayan Obo carbonatite, I have used examples of anorogenic alkaline complexes and carbonatites that are effectively pristine and unaffected or little influenced by later geological events. In this context, I report on two alkaline complexes and associated mineralisation in Namibia (Brandberg and Erongo) related to the opening of the South Atlantic and the Parana-Etendeka large igneous province. With regard to carbonatites and associated mineralisation, I discuss the exceptionally well-preserved Kruidfontein and Goudini in South Africa, Mount Weld and Gifford Creek ferrocarbonatite complex in Western Australia, the controversial Bayan Obo in northern China and the carbonatites of the Mianning-Dechang belt in SW China. It is proposed that all these igneous systems are formed by processes of partial melting in metasomatised lithospheric mantle, induced by upwelling mantle plumes. Furthermore, it is contended that these alkaline and carbonatite igneous systems are generally formed in the distal sectors of a mantle plume due to lateral transfer of volatiles, resulting in low degrees of partial melting in the metasomatised sub-continental lithospheric mantle. (C) 2014 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.