Sources and evolution of arc magmas inferred from coupled O and Hf isotope systematics of plutonic zircons from the Cretaceous Separation Point Suite (New Zealand)

Abstract

Coupled O and Hf isotopic compositions of zircons from Early Cretaceous (113-124 Ma) granitoids of the Separation Point Suite (SPS), New Zealand, obtained by cathodoluminescence imaging-guided micro-beam methods (SIMS, LA-ICPMS), are used as a record of evolving magma compositions in a prominent Mesozoic arc system. Eight representative SPS samples from individual plutons in the Nelson and Fiordland regions yield magmatic zircons with initial Hf isotope ratios (expressed in εHf) ranging from - 4 to + 11 (Nelson) and + 5 to + 12 (Fiordland), respectively. Initial Hf isotope ratios of zircons are extremely heterogeneous within individual samples, with the vast majority of values distinctly les..