| Popis: |
Active volcanoes pose a significant natural hazard. In order to evaluate the hazard it is important to reconstruct the history of such volcanoes to understand the frequency, style of eruption and the areas typically affected by the explosive eruptions. This thesis focuses on deciphering the volcanic and magmatic record for one of the most productive volcanoes in southern Chile, Volcán Mocho-Choshuenco. Work presented in the thesis establishes a detailed record of the explosive activity during the last 18 kyrs, constructed using field observations and geochemical analyses of the eruption deposits. Using a multi-technique approach Mocho-Choshuenco is shown to be one of the most explosive, frequently active and hence hazardous volcanoes in Chile. This high-resolution eruptive record provides new constraints on the underlying causes of spatial and temporal variability in arc volcanism. Temporally, the record gives new understanding into the response of arc volcanoes to deglaciation; clear temporal variation in eruption flux, eruption size and magma composition are observed. This time-varying behaviour is hypothesised to reflect changes in the crustal plumbing system, and magma storage timescales in response to removal of an ice-load. It demonstrates that deglaciation can drive changes in eruption behaviour at arc volcanoes; however the response is more complex and subtle than settings where decompression melting dominates. Spatially, Mocho-Choshuenco has a high number and density of scoria cones that have erupted relatively primitive magmas but nonetheless with a wide range of magma compositions. For some of the 'classical' slab and mantle geochemical tracers the erupted magmas span the complete range seen in this part of the arc. The tight temporal and spatial constraints provided by the analysed samples, coupled with recent advances in numerical modelling of magma transport through subduction zones, enable new hypotheses for interpreting the signatures of mafic arc magmas to be defined. |
