Hikurangi Plateau: A Cretaceous large igneous province in the southwest Pacific Ocean

Abstract

The first dredge haul of basement rocks obtained from the Hikurangi Plateau in the southwest Pacific Ocean consists dominantly of volcanic and volcaniclastic rocks of probable pre–Late Cretaceous age. All samples have undergone extensive seafloor weathering to phyllosilicate‐ and zeolite‐bearing assemblages. Petrography, mineral chemistry, and whole rock element concentrations and ratios of the least altered lavas (e.g., TiO2 = 1.3–1.6 wt%, Cr = 132–224 ppm, Zr/Y = 2.9–3.6, Zr/Nb = 19–29, Ti/V = 22–29) suggest a restricted igneous compositional range broadly comparable with normal to enriched mid‐ocean ridge basalt. However, isotopic compositions of leached samples (87Sr/86Sri = 0.70361–0.70374, εNdi = 5.7–6.2) are comparable with oceanic island basalt suites. Collectively, these petrological characteristics are similar to rocks from large igneous provinces of Cretaceous age in the western Pacific Ocean (e.g., Manihiki and Ontong Java Plateaus). Consequently, we interpret the Hikurangi Plateau as another of these Early Cretaceous basaltic oceanic plateaus. Speculatively, parts of the obducted Tangihua and Matakaoa igneous complexes of the North Island may have been derived from the Hikurangi Plateau as the plateau collided with the New Zealand continent in the early Miocene.