PhD defence: Quinten van der Meer
Quinten van der Meer defends his PhD thesis,
The timing and sources of intraplate magmatism related to continental breakup in southern New Zealand
Professor Tod Waight, IGN
Associate Professor Paul Martin Holm, IGN (chairman)
Professor Valentin Troll, University of Uppsala - Sweden
Professor Kaj Hoernle, Geomar, Kiel - Germany
The long history of New Zealand as Gondwana’s eastern active margin ended at ~110 Ma when extensional tectonics initiated. In New Zealand’s inboard Western Province this is expressed in the formation of metamorphic core complexes and the syn-tectonic intrusion of the latest large scale subduction related I- to I/S-type plutons of the Rahu suite up to 105 Ma. Isolated plutonism continued on a smaller scale after 105 Ma. O and Hf isotopes in zircon from later felsic plutons indicate waning subduction related magmatism up to 101 Ma. This is followed by the regional dominance of intraplate signatures. This is also manifested in the intrusion of extension related dikes from ~92 Ma to ~84 Ma followed by opening of the Tasman Sea and a second event between 72.5 and 68 Ma.
Detailed chemical and Sr-Nd-Hf-Pb isotopic investigations of these dikes suggest an intraplate source highly enriched in incompatible elements. A subset of the most primitive samples with SiO2 <46 wt.% have compositions that are compatible with melting of variable proportions of hornblendite (±apatite ±phlogopite ±rutile ±clinopyroxene) and depleted peridotite. These observations are in accordance with decompressional melting of lithospheric mantle with HIMU-type enriched veins. Chemical similarities suggest that contemporaneous and younger intraplate magmatism in New Zealand may also be derived from the same or similar sources.
The thesis is available from the PhD administration office, 04.1.409