Remnants of Gondwanan continental lithosphere in oceanic upper mantle: Evidence from the South Atlantic Ridge

Abstract

Dredged glass from the southern Mid-Atlantic Ridge near the Bouvet Triple Junction has unique major element, trace element, and isotopic composition, distinct from typical mid-ocean ridge basalts. It is a high-Mg (Mg# 67.8), high-Ni (NiO 290 ppm) andesite depleted in highly incompatible and heavy rare-earth elements with an isotopic signature of ancient continental lithosphere (i.e., low 206Pb/204Pb and 143Nd144Nd and high 87Sr/86Sr and δ18O). The origin of this glass is attributed to melting of a Precambrian garnet bearing, mafic lithology, possibly related to lower crustal blocks stranded in the upper mantle during breakup of Gondwana and opening of the Atlantic. This composition can be us..