Superplumes from the deep mantle



A new and dramatic interpretation of mantle convection is emerging from the record of massive volcanic eruptions that have occurred episodically throughout Earth's history. The most recent volcanic outburst began suddenly at about 125 million years ago and continued for at least 60 million years, spanning much of the Cretaceous period. According to a recently completed study, the rate of ocean crust production during that burst was approximately twice what it is today [Larson, 1991). Much of this activity appears to have been produced by the melting of one, or perhaps several, massive thermal plumes that rose from the deep mantle beneath the Pacific and Indian plates. Cretaceous age continental flood basalts such as the Deccan Traps in India fit this picture nicely. Several large ocean plateaus such as Ontong-Java in the southwest Pacific and Kerguelen in the south Indian Ocean date from this period, and were probably formed in a similar way. These plateaus consist of 20-50 million cubic kilometers of plume-derived basaltic crust.