Textural and chemical variation in plagioclase phenocrysts from the 1980 eruptions of Mount St. Helens,USA |
| |
| Authors: | Kim Berlo Jon Blundy Simon Turner Chris Hawkesworth |
| |
| Institution: | (1) Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s road, BS8 1RJ Bristol, UK;(2) Department of Earth and Planetary Sciences, McGill University, 3450 University Street, H3A 2A7 Montreal, QC , Canada;(3) GEMOC, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW, 2109, Australia |
| |
| Abstract: | This study presents major- and trace-element chemistry of plagioclase phenocrysts from the 1980 eruptions of Mount St. Helens
volcano. Despite the considerable variation in textures and composition of plagioclase phenocrysts, distinct segments have
been cross-correlated between crystals. The variation of Sr and Ba concentration in the melt, as calculated from the concentration
in the phenocrysts using partition coefficients, suggests the cores and rims crystallised from compositionally different melts
offset by the plagioclase crystallisation vector. In both of these melts Sr and Ba are correlated despite the abundance of
plagioclase in the 1980 dacites. We propose that rapid crystallisation of plagioclase upon magma ascent caused a shift in
melt composition towards lower Sr and higher Ba, as documented in the rims of the phenocrysts. Although the cores of the phenocrysts
crystallised at relatively shallow depths, they preserve the Sr and Ba of the deep-seated melts as they ascended from a deeper
region. Further magma ascent resulted in microlite nucleation, which is responsible for a similar shift to even lower Sr concentration
as observed in the groundmass of post-18 May 1980 samples.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
| |
| Keywords: | Mount St Helens Plagioclase Nucleation Crystallisation Sr and Ba |
| 本文献已被 SpringerLink 等数据库收录！ |
|
