Emeritus Professor Alan Cooper, Department of Geology, University of Otago
The Haast Schist of New Zealand, composed predominantly of Otago, Alpine and Marlborough Schist components, is the most deeply buried and strongly metamorphosed part of a broadly eastward younging accretionary complex developed on the subduction margin of Gondwana.
The Torlesse Composite terrane protoliths that grade into schist range in age from Carboniferous to Triassic. They were multiply deformed and metamorphosed in the Jurassic. However, extensive areas of Alpine Schist in the west, in part overlying a metamorphosed ophiolitic sequence, and rich in metabasite and metachert, have been shown to have anomalous detrital zircon ages, as young as ~108 Ma.
This deposition occurred approximately synchronous with both the cessation of westward-directed subduction in the Eastern Province of New Zealand, and localised covering of the erosion surface in the now contiguous Otago Schist to the east by extensional terrestrial and volcanoclastic sediments.
These Mid Cretaceous schist protoliths are interpreted to form the exotic Pounamu terraneaccreted and interfolded with the Otago Schist on the western margin of Southeast Zealandia.
The accompanying metamorphism on the tectonic margin between SE and NW Zealandia microplates is dated from zircon overgrowths on detrital grains at 69 Ma (although over an extended period, 64 to 98 Ma, regionally). The Haast Schist is therefore a polygenetic unit formed from the two-sided amalgamation of polyphase metamorphic components.
|Date||Wednesday, 9 May 2018|
|Time||5:00pm - 6:00pm|
|Location||Quad 4 Lecture Theatre, Geology Building, 360 Leith Street, Dunedin|