Geology of New Zealand’s Sub-Antarctic Islands

Abstract

ABSTRACT New Zealand s remote five Sub-Antarctic island groups are the only sub-aerial exposures of the ∼800,000\u2005km2 Campbell Plateau portion of Zealandia. An up-to-date geological map, a summary of the current geological knowledge and a geological interpretation is presented for each island group. The oldest rocks are Early Paleozoic metasediments on Campbell Island/Motu Ihupuku. Granitoids dominate the Bounty Islands/Moutere Hauriri (Early Jurassic) and Snares Islands/Tini Heke (Early Cretaceous), form a small part of the Auckland Islands/Motu Maha (Late Cretaceous), and occur as rare Cretaceous xenoliths in tuffs on the Antipodes Islands/Moutere Mahue. The Campbell Island/Motu Ihupuku metasedimentary rocks are overlain by Late Cretaceous-Cenozoic basin sediments, which are in turn overlain by tuff and lava resulting from emergent intraplate volcanism. The Auckland Islands/Motu Maha and Antipodes Islands/Moutere Mahue stratigraphies are also related to emergent intraplate volcanism. Limited radiometric dating indicates that the Auckland Islands/Motu Maha breached the Southern Ocean in the Early-Middle Miocene, Campbell Island Volcano formed in the Late Miocene, and the Antipodes Volcano formed in the last 300,000 yrs. Basaltic dikes on the Snares Islands/Tini Heke are undated, and mafic dikes on the Bounty Islands/Moutere Hauriri are Mesozoic; it is unclear when these two island groups formed. The Auckland Islands/Motu Maha and Campbell Island/Motu Ihupuku have cirques, terminal and lateral moraines, till deposits and glacially carved fjords, and near-shore bathymetry indicates that all island groups exposed significantly larger areas during glacial periods. More work is required to understand the geological formation of these islands and their Southern Ocean climatic records.