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Whole-rock geochemical reference data for Torlesse and Waipapa terranes, North Island, New Zealand

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journal contribution
posted on 22.10.2015 by RC Price, N Mortimer, IEM Smith, R Maas

Sixteen metasedimentary rocks from the Waipapa and Torlesse composite terranes of New Zealand’s North Island have been analysed for major and trace elements and Sr, Nd and Pb isotope composition. The new data provide a comprehensive analytical dataset that can be used for quantitative trace element and isotopic modelling of the petrogenesis of Neogene North Island volcanic rocks. The major and trace element and isotope data confirm previously recognised systematic compositional differences between Waipapa and older Torlesse (Kaweka Terrane) metasedimentary rocks. Kaweka Terrane samples tend to have higher SiO2, Al2O3, Cs, Rb, Th, U, Hf and total rare earth elements (REE) abundances and chondrite normalised REE patterns characterised by light/heavy REE enrichment. Fe2O3, MgO, Sr and Sc contents are lower in Kaweka samples than those observed in their Waipapa Terrane counterparts. 87Sr/86Sr ratios are lower and 143Nd/144Nd values are higher in Waipapa compared to Kaweka samples, and Pb is isotopically more radiogenic in the Kaweka samples. Younger Torlesse (Pahau Terrane) samples have major and trace element and isotopic compositions that span the Waipapa and Kaweka suites, but overall they are more similar to the former. Mudstones from all terranes converge in bulk composition and there are systematic differences in isotopic composition between mudstones and sandstones from the Kaweka and particularly the Waipapa terranes. Both lithologies need to be considered when estimating the compositions of metasedimentary terranes. Major and trace element and isotope compositions of the metasediments indicate a complex provenance involving subduction-related volcanic and crustal or continental inputs.