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Mixed Magmas, Mush Chambers and Eruption Triggers: Evidence from Zoned Clinopyroxene Phenocrysts in Andesitic Scoria from the 1995 Eruptions of Ruapehu Volcano, New Zealand |
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| Authors: | NAKAGAWA MITSUHIRO; WADA KEIJI; WOOD C PETER |
| Institution: | 1DIVISION OF EARTH AND PLANETARY SCIENCES, GRADUATE SCHOOL OF SCIENCES, HOKKAIDO UNIVERSITY, N10 W8 KITA-KU, SAPPORO, 060-0810, JAPAN 2DEPARTMENT OF EARTH SCIENCES, HOKKAIDO UNIVERSITY OF EDUCATION, ASAHIKAWA, JAPAN 3INSTITUTE OF GEOLOGICAL AND NUCLEAR SCIENCES, WAIRAKEI RESEARCH CENTRE, TAUPO, NEW ZEALAND |
| Abstract: | Juvenile ejecta from the September and October 1995 eruptionsof Ruapehu volcano, New Zealand, indicate that mixing occurredbetween relatively higher- and lower-temperature (high-T andlow-T) andesitic magmas. Compositional zonations in clinopyroxenephenocrysts provide direct evidence for a pre-eruption crystal–meltmush chamber containing low-T magma, and elucidate the processesof magma mixing and eruption, following the injection of high-Tmagma. Many phenocrysts with Fe-rich cores derived from low-Tmagma have extremely reverse zoned mantles around slightly resorbedcores. Mg-value 100Mg/(Mg + Fe)] increases from 65–70to |
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