Cold magmas and explosive eruptions: The story of zircon from Mount Pinatubo, Philippines
Abstract
Explosive volcanic eruptions can have large impacts on their environments, from local societies to global climate. The 1991 eruption of Mount Pinatubo is one of the largest in the 20th century, as it released 10000 Mt of pyroclastic material and 20 Mt of SO2 gas. Previous work suggested that the eruption was triggered by injection of hot mafic magma into a cool dacite magma reservoir ( 780°C and 47 vol.% crystallinity). Our new zircon and glass data suggest that this reservoir was much cooler than previously considered. Ti-in-zircon geothermometry (Ferry and Watson, 2007) yields crystallization temperatures ranging 635-734°C (± 34°C). The calculation used 0.9 for the activity of TiO2 based on measured glass composition at 700-780°C. The crystallization temperatures are consistent with the zircon saturation temperature of 739°C based on glass composition and using the method of Watson and Harrison (1983). Furthermore, applying the pressure correction of -5°C/0.1 GPa suggests that magma may have been as cool as 595°C. The equation of Hui and Zhang (2007) for hydrous melt and the Einstein-Roscoe equation yield viscosities of 108.5, 107.4 and 106.6 Pa · s at 600°C, 700°C and 780°C, respectively. This suggests that the magma was up to two orders of magnitude more viscous than previously thought. Altogether, we envision that the cool ( 700°C or lower) and highly viscous magma explains the particularly explosive eruption of Mount Pinatubo witnessed in 1991.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.U11B..20L
- Keywords:
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- 0810 Post-secondary education;
- EDUCATION