Abstract

Large igneous provinces, representing prodigious volumes of basalt erupted through continental and oceanic crust, are believed to be associated with high-temperature mantle plumes incident at the base of the lithosphere. Recent "plume initiation" models for continental flood-basalt volcanism suggest that material in the plume will intersect the solidus shortly after arriving, or impacting, beneath the lithosphere, so that melting is near-synchronous with plume impact. Beneath continents, however, melting of a plume head is inhibited by the presence of a thick (>125 km) mechanical boundary layer, which must be thinned and removed by conductive heating and melt injection before significant basalt production can occur. This necessitates a period of plume incubation, characterized by lithosphere extension and doming, by the establishment of long- lived paleodrainage patterns, and, laterally, by the intrusion of alkalic magmas. Field evidence from rive major igneous provinces indicates that plume incubation is a more appropriate model than simple plume impact for continental flood-basalt volcanism.

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