A new paper from Dr. Tyrone Rooney, Dr. Barry Hanan, and others present a geochemical study of Ethiopian Miocene intraplate alkaline lavas: melts of a lithospheric mantle that was enriched metasomatically during lithospheric stabilization and by recent plume-lithosphere interaction.
The role of continental lithosphere metasomes in the production of HIMU-like magmatism on the northeast African and Arabian plates
Tyrone O. Rooney1, Wendy R. Nelson2, Laure Dosso3, Tanya Furman4 and Barry Hanan5
1Department of Geological Sciences, Michigan State University, East Lansing, Michigan 48824, USA
2Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas 77204, USA
3Centre National de la Recherche Scientifique, UMR 6538, Domaines Océaniques, 29280 Plouzané, France
4Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA
5Department of Geological Sciences, San Diego State University, San Diego, California 92182-1020, USA
Abstract
Intraplate alkaline lavas typically exhibit isotopic characteristics that require a source with long-term isolation from the convecting asthenosphere, such as in the sub-continental lithosphere mantle or a mantle boundary layer. Melting of metasomatically enriched domains, or metasomes, within the lithospheric mantle provides a viable mechanism for generating the geochemical characteristics of intraplate alkaline basalts. The origins and distribution of these metasomes have been attributed to recent enrichment of the lithosphere by a mantle plume or ancient events that occurred during the early evolution of the sub-continental lithosphere mantle. Here, we present a geochemical study of Ethiopian Miocene intraplate alkaline lavas: melts of a lithospheric mantle that was enriched metasomatically during lithospheric stabilization and by recent plume-lithosphere interaction. We find that these lavas have geochemical characteristics consistent with melting of an amphibole-bearing lithospheric-mantle metasome. New Pb and Hf isotope data for these lavas require a HIMU-like source component, similar to other alkaline lavas erupted through the Horn of Africa, Sudan, and Egypt, and adjacent Arabian plate lithospheres. The isotopic characteristics of this component are distinct from the Afar plume mantle source and instead are consistent with the long-term evolution of a lithospheric metasome created during a Neoproterozoic subduction event associated with the Pan-African orogeny. The widespread distribution of easily fusible lithospheric metasomes within the continental lithosphere mantle may facilitate magma generation without the need for substantial lithospheric thinning or elevated mantle potential temperatures. Mantle heterogeneity of this nature has implications for the source origin of HIMU magmas associated with continental lithosphere.
