Constraining the structure of arc crust is critical to our understanding of arc magmatic systems and to test the hypothesis that continental crust is generated at arcs (e.g. Tay- lor, 1967). In this study, petrological information has been combined with information on rock physical properties from laboratory measurements and theoretical calculations to produce the most thoroughly constrained model to date of the structure of the crust beneath the active volcanic island of Montserrat. Ultrasonic velocity measurements together with the seismic tomography model of Paulatto et al. (2012), support geological evidence that andesite dominantly comprises the shallow crust. Igneous crustal inclusions found in host andesite and high velocity regions identified in the seismic tomography model are consistent with shallow intrusive complexes beneath the three volcanic centres. A low velocity region is distinguished in the seismic tomography model beneath the currently active Soufriere Hills centre, most likely due to the presence of melt. The volume of this magma storage region is highly dependent on the geometry of melt pockets. Using constraints from this study, the best model to explain this low velocity zone is a magma storage region between 5.5-7.5 km depth with a volume of ~13 km ' and melt fraction of ~0.30-0.35 (Paulatto et al., 2012). Cumulate-textured inclusions provide direct evidence for fractional crystallisation at Montserrat. Thermobarometry calculations indicate that most of these inclusions crystallised between 3-6 km depth, providing further evidence in support of a shallow magma chamber. Some inclusions however, including one erupted in the current eruption, are calculated to have formed at depths of up to 22 km from a highly water-rich magma with up to 8.9 ±1.3 wt% H20. Magma may therefore be ascending from the lower crust to feed the current eruption.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:558080 |
| Date | January 2011 |
| Creators | Kiddle, Emma Jane |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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