Komatiites and picrites: evidence that the 'plume' source is depleted

Abstract

High-temperature magmas such as picrites and komatiites are candidates for the material in the hot axial region of mantle plumes. In current plume theories these magmas should have an enriched ocean-island basalt (OIB) type chemistry. High MgO magmas, however, are often more like depleted mid-ocean ridge basalts (MORB) in trace element and isotopic chemistry. This is a paradox for deep mantle plume, or primitive mantle, theories but is expected if hotspots and MORB share a common depleted source and the transition to OIB chemistry involves shallow-level cooling, crystal fractionation and contamination. Ancient komatiites appear to have come from the same deep depleted reservoir as modern picrites and MORB.

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© 1994 Elsevier Science B.V. Received 11 June 1994; accepted 29 August 1994. I appreciate the comments of Bruce Marsh. I thank Eleanor and John R. McMillan and their family for their support. This research was also supported by NSF Grants No. EAR-9002947 and EAR-9218390. Contribution No. 5323 Division of Geological and Planetary Sciences, Caltech, Pasadena, CA 91125.

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