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Abstract
Altered lavas have been dredged from three locations on the Resolution Ridge, west of New Zealand's South Island. On the basis of whole-rock geochemistry, Sr, Nd and Pb isotope data and Ar–Ar ages, they can be divided into two suites: 62–60 Ma enriched mid-ocean ridge basalt (E-MORB), and 57 Ma trachybasalt and trachyandesite of ocean island basalt (OIB) affinity. The E-MORBs from the Resolution Ridge are only the second place from which Tasman Sea abyssal oceanic crust has ever been sampled, they have Indian MORB-like isotope compositions, and their ages support a recent interpretation of a 100 km sinistral offset of the southern part of the Tasman Sea spreading ridge. The slightly younger OIB suite erupted shortly after oceanic crust formation and has FOZO to HIMU source characteristics similar to the well-known SW Pacific Diffuse Alkaline Magmatic Province (DAMP). The close occurrence and isotopic mixing relationships of both Paleocene volcanic suites on the Resolution Ridge may be explained by a heterogeneous upper mantle in which the more fertile OIB component was extracted during a later melting event away from the spreading ridge. The dredged lavas predate formation of Southeast Tasman oceanic crust that borders the Resolution Ridge to the south.
Acknowledgements
We thank the captain, crew and scientists on board the R/V Tangaroa TAN0006 cruise for recovery of the rock samples, Land Information New Zealand (LINZ) for permission to use the rocks obtained from UNCLOS cruise, and Ministry of Foreign Affairs and Trade (MFAT) for approving publication of this paper. Initial examination of the dredged rocks was done with Rick Herzer. Laboratory and office work were funded by the New Zealand Ministry of Science and Innovation's core funding to GNS Science. Earlier versions of the manuscript were improved by comments from François Bache, Christian Timm, Christoph Beier and an anonymous reviewer.