Age and petrogenetic constraints on the lower glassy ignimbrite of the Mount Somers Volcanic Group, New Zealand
| Autor: | Q. H. A. Van der Meer, Tod E. Waight, Tom Andersen, Martin J. Whitehouse |
|---|---|
| Rok vydání: | 2017 |
| Předmět: |
geography
Sensitive high-resolution ion microprobe geography.geographical_feature_category Younger age 010504 meteorology & atmospheric sciences Geochemistry Geology Magma chamber 010502 geochemistry & geophysics 01 natural sciences Geophysics Volcano Group (stratigraphy) Earth and Planetary Sciences (miscellaneous) Upper crust Period (geology) 0105 earth and related environmental sciences Zircon |
| Zdroj: | New Zealand Journal of Geology and Geophysics. 60:209-219 |
| ISSN: | 1175-8791 0028-8306 |
| Popis: | The Mount Somers Volcanic Group (MSVG) forms a large (c. 18,000 km2) calc-alkaline volcanic complex on New Zealand’s Eastern Province. U–Pb secondary ion mass spectrometry (SIMS) spot ages on zircon from the lower glassy ignimbrite in Rakaia Gorge reveal a bimodal distribution of 99.0 ± 0.5 and 96.3 ± 0.5 Ma (2σ). These ages are within error of previous (unpublished) zircon sensitive high resolution ion microprobe ages but have a precision that enables identification of two distinct episodes of zircon crystallisation, indicating magmatic activity over a period of at least 2.5 Ma. The younger age is interpreted to represent the emplacement age of the ignimbrite. The older age may originate from the assimilation of underlying ignimbrites or prolonged magma chamber processes. Combined O and Hf isotopes in zircon indicate that melt compositions for the c. 99 and c. 96 Ma magmatic episodes were very similar and intermediate between the local upper crust and mantle-derived melts, supporting formation th... |
| Databáze: | OpenAIRE |
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