Petrological record from young Ruapehu eruptions in the 4.5 ka Kiwikiwi Formation, Whangaehu Gorge, New Zealand

• Published in: New Zealand journal of geology and geophysics Vol. 56; no. 3; pp. 121 - 133
• Main Authors: Auer, A, White, JDL, Nakagawa, M, Rosenberg, MD
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis Group 01.09.2013; Taylor & Francis Ltd
• Subjects: andesite; clinopyroxene; geobarometry; Magma; magma plumbing; mineral chemistry; mush column; plagioclase; Ruapehu volcano; PSE, New Zealand
• ISSN: 0028-8306; 1175-8791
• DOI: 10.1080/00288306.2013.796998

A petrological study of the Kiwikiwi Formation from Mount Ruapehu is presented. We apply mineral thermobarometry to investigate the volcano's plumbing system and the petrogenesis of the Kiwikiwi andesite. The earliest petrographic record is preserved in rare orthopyroxene-plagioclase (X An >85) glomerocrysts and scarce highly resorbed olivine. A traverse of the magma through an extensive crustal mush column resulted in crystallisation of a two pyroxene-plagioclase andesite. Complex mineral zonation and a large range of glass composition was the result of the frequent intrusion of small magma batches into the system. The range of mineral and end-member liquid compositions suggest that crystallisation commenced at c. 25 km depth. Subsequent ascent through the crust added considerable textural complexities but resulted in only little net loss to cumulate phases. The last magma storage occurred at crustal levels of c. 5 km depth prior to the eruption of a highly porphyritic andesitic magma.