Geology, petrology, and petrogenesis of Little Barrier Island, Hauraki Gulf, New Zealand

Abstract

Little Barrier Island is the emergent part of a large, isolated, dacite-rhyodacite volcano in the active Hauraki Rift, 80 km northeast of Auckland. Two volcanic episodes are recognised: Waimaomao Formation was emplaced as a rhyodacite dome at 3 Ma, whereas the more extensive dacitic lavas of Haowhenua Formation were erupted between 1.2 and 1.6 Ma. All Little Barrier lavas are strongly porphyritic and contain phenocrysts of plagioclase, orthopyroxene, and hornblende. Geochemically, they are subduction related and distinct from the older lavas of the Coromandel Volcanic Group, being Zr rich but Rb and Ba poor. Their Sr and Nd isotope ratios are similar to those of the Tonga-Kermadec arc volcanoes. Modelling of the dacite supports petrographic evidence that recharge and mixing were important in the magmatic system. Little Barrier and two dacite domes of similar age and composition near Whangarei form a northwest-trending lineament subparallel to the Alexandra Volcanics and the Vening Meinesz Fracture Zone.

Genetic divergence between isolated populations of the North Island New Zealand Rifleman (Acanthisitta chloris granti) implicates ancient biogeographic impacts rather than recent habitat fragmentation

“…Given those provisos, the genetic separation of the Insular and all mainland sites appears to substantially predate human occupation of the New Zealand archipelago (approx. 1,000 years ago) and is consistent with the long geological isolation of this volcanic island (Hauturu-o-Toi/Little Barrier), which is estimated to have emerged approximately 3 mya with subsequent eruptions at approximately 1.6 mya (Lindsay et al, 1999). Land-bridges to the mainland (approx.…”

“…40 km to the south) are likely to have formed at least once during the Pleistocene, when glacial maxima would have caused significant lowering of sea levels (Chapple et al, 2008;Hamilton & Atkinson, 1961;Hare et al, 2008;Lindsay et al, 1999;Turbott, 1961). Nearby mainland populations of Rifleman are now regionally extinct (Robertson et al, 2007); therefore, more fine-scale patterns of gene flow Mitchell et al (2016).…”

Orthopyroxene, augite, and plagioclase compositions in dacite: application to bedrock sourcing of lithic artefacts in southern British Columbia

“…Dacites from around the Pacific rim (e.g., South America, southern Asia, South Pacific) and the Mediterranean (Ujike et al 1999;Lindsay et al 1999;Matthews et al 1999;Pe-Piper and Piper 1994) commonly contain microphenocrsyts of orthopyroxene, augite, and plagioclase. This hints at the potential for widespread practical application of mineralogical fingerprinting in provenance studies.…”

K‐Ar ages of early Miocene arc‐type volcanoes in northern New Zealand

“…Much younger ages of 0.8 ± 0.1 and 1.2 ± 0.1 Ma have been obtained from Parakiore and Hikurangi Domes, respectively (Lindsay et al 1999 Fig. 8 Histograms of timing and duration of activity of arc-type volcanism in northern New Zealand between 25 and 15 Ma, as indicated by K-Ar dating (this paper), biostratigraphic dating (Hayward 1993; this paper), and seismic stratigraphic analysis beneath the western continental shelf (Herzer 1995).…”