Pb-Sr-Nd-O isotopic constraints on the origin of rhyolites from the Taupo Volcanic Zone of New Zealand: evidence for assimilation followed by fractionation from basalt

Abstract

A comprehensive Sr-Nd-Pb-O isotopic study is reported for rhyolites from the Maroa Volcanic Centre in the Taupo Volcanic Zone (TVZ) of New Zealand. The Sr-Nd isotopic compositions of the rhyolites (87Sr/86Sr=0.705236 to 0.705660 and e{open}Nd = 2.0 to 0.2) are intermediate between those of primitive basalts (87Sr/86Sr=0.70387 and e{open}Nd = 5.3) and the Torlesse basement (87Sr/86Sr=0.709 and e{open}Nd = -4.5). The relatively low 'mantle-like' oxygen isotopic compositions of δ18 O = 7 ± 0.5 are consistent with the Nd-Sr isotopic constraints in that they can be accounted for by ∼15% to 25% crustal contamination of a basaltic parent by relatively δ18 O-rich Torlesse metasediment. High precisio..