Komatiites are ancient volcanic rocks, mostly from the Archaean era, that formed through high degrees of partial melting of the mantle and therefore provide reliable information on bulk mantle compositions. Here it is shown that most early Archaean komatiites from the Barberton greenstone belt of South Africa and the Pilbara craton of Western Australia are depleted in platinum group elements (PGEs) relative to late Archaean and younger komatiites, and the variations of this depletion with time suggests that PGE-enriched cosmic material was progressively mixed into the deep mantle.
- Wolfgang D. Maier
- Stephen J. Barnes
- R. Hugh Smithies
