The Geoscience Society of New Zealand’s 2018 Hochstetter Lecture
The Pounamu Terrane: a new component in the assembly of Zealandia
Emeritus Professor Alan Cooper,
Geology Department, University of Otago
Date: Monday, 17th of September, at 7.30pm
Venue: Hawke’s Bay Regional Council,
corner Vautier and Dalton Streets, Napier
Admission: Gold coin donation
Stretching from the Hokitika River in Westland through to the Dunstan Range in Central Otago, the Pounamu terrane is a newly-identified component of the ancient Zealandia continent. Zealandia now is largely submerged (excepting the islands of New Zealand and New Caledonia), but it broke away from Australia and Antarctica between 85 and 60 million years ago.
Professor Cooper details how the Pounamu terrane is much younger than the adjoining components of New Zealand’s Eastern Province and formed after the original subduction zone, situated at the Chatham Rise, was blocked by collision of the Hikurangi Plateau approximately 105 million years ago. This collision ended a 200 million year phase of west-dipping subduction during which marine sediments scraped off the subducting oceanic crust were assembled to form the Eastern Province of New Zealand. The deeper levels of these off-scraped sediments were metamorphosed by extreme heat and pressure, producing the Haast Schist (dominated by Otago, Alpine and Marlborough schists).
However, new evidence suggests that a second subduction zone developed subsequently on the western margin of the South Island with off-scraped sediments, making up the Pounamu terrane, accumulating above an east-dipping subduction zone. Deep in the subduction zone, the Pounamu terrane underwent metamorphism at around 70 million years ago forming this younger component of the Alpine Schist.
Alan was educated in Burton-on-Trent and Sheffield, England. He came to New Zealand in 1966 as a Teaching Fellow to undertake PhD study at the University of Otago, under Professor Douglas Coombs. His thesis area was the Haast River, south Westland, where he investigated the structure and progressive metamorphism of greenschists and amphibolites in the Alpine Schist. In 1970, he was appointed a Lecturer at the University of Otago, from where he retired in 2012 after 46 years service.
Alan continues to do research work in the Southern Alps. Subjects of his research include: a lamprophyre-carbonatite dyke swarm intruding the schist (first documented by Julius von Haast); the Pounamu Ultramafics and correlative rocks; marine terrace remnants and uplifted Holocene sedimentary sequences; mapping of the Alpine Fault; anatectic pegmatites; ages of detrital zircons within the Alpine Schists. He has undertaken experimental work on carbonate minerals in Canada, and mapping of carbonatites in Antarctica, Namibia and Turkey. He has spent eight field seasons in Antarctica: supervising students and investigating the basement geology of the Transantarctic Mountains and the Neogene to Recent alkaline volcanic rocks of the Erebus Province of the McMurdo Volcanics.
The Hochstetter Lecture is named in honour of Ferdinand von Hochstetter and a speaker is chosen annually by the GeoScience Society of New Zealand. Hochstetter is known for the geological maps of the Auckland and Nelson areas produced in conjunction with colleague Julias Haast whilst on a scientific voyage in 1859.