Crystal size distributions and other quantitative textural measurements in lavas and tuff from Egmont volcano (Mt. Taranaki), New Zealand |
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Authors: | Michael D Higgins |
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Institution: | (1) Sciences de la Terre, Université du Québec à Chicoutimi, Chicoutimi, G7H 2B1, Canada, CA |
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Abstract: | The size, shape and orientation of plagioclase crystals have been quantified in a tuff and series of andesite lavas from
the active Egmont volcano (Mt. Taranaki), New Zealand. Linear crystal size distributions (CSDs) show that if the magma had
several components, then only one provided the crystals. The slope of the CSD indicates that the earliest lavas measured had
a residence time of ∼50 years in the magma chamber for a growth rate of 10–11 cm/s. Subsequent lavas had slightly longer residence times (50–75 years), but the following series returned to 50-year residence
times. The youngest magmas, from both Egmont summit and the parasitic Fantham's Peak, have the shortest residence times of
∼30 years. Variations in residence time may reflect changes in the magma chamber shape or depth, or the temperature of the
surrounding rocks. Crystal shapes and zonation suggest that crystallization occurred in a bottle-shape magma chamber, and
not in a narrow conduit. If future eruptions use the same magma chamber as the most recent eruptions, then a delay of approximately
30 years can be expected between refilling and eruption.
Received: 25 October 1995 / Accepted: 19 April 1996 |
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Keywords: | CSD Residence time Egmont volcano Mt Taranaki Crystal shape Crystal orientation Magma chamber |
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