Contrasting high field strength element contents of continental flood basalts from plume versus reactivated-arc sources

Abstract

Published geochemical data pertaining to global continental flood basalts (CFBs) indicate that there are two contrasting distributions of high field strength elements (HFSEs) plotted on silicate Earth-normalized spider diagrams. Most CFBs plot close to a standard oceanic island basalt (OIB) line and are the product of magma from a mantle plume head mixed to varying degrees with magma from other sources. The compositional diversity of the OIB-like basalts is consistent with the interaction of plume heads with diverse mantle layers during gradual emergence followed by plume-tail magmatism along hotspot tracks. On the other hand, at least three CFBs, including those in the Central Atlantic magmatic province, the Siberian Traps, and the Lesotho basalt province of South Africa, plot close to a standard arc-basalt line. These arclike basalts contain virtually the same average HFSE contents. The much lower HFSE contents of the arclike CFBs are consistent with a sudden reactivation of dormant arc or backarc sources trapped under continental-plate sutures.