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Title: Degassing of volatiles and semi-volatile trace elements at basaltic volcanoes
Author: Collins, S. J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2009
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At Mt. Etna, Italy, vigorous gas-rich eruptions in 2001, 2002 and 2003 were followed by gas-poor eruptions in 2004, 2006 and 2007. Contrary to expectation, melt inclusion compositions indicate that magmas erupted between 2004 to 2007 did not follow similar degassing paths as recorded in 2001 and 2002 and that are expected from the solubility laws of CO2 and H2O. Instead melts stored in the plumbing system since 2002 reequilibrated with CO2-rich gases from depth. Sustained gas percolation caused loss of water and enhancement of CO2 in the evolving melt. At Piton de la Fournaise melt inclusions trapped in olivines record degassing of various batches of magma and the fractionation of olivines at various depths within the plumbing system. The host melt which carries these olivines to the surface represents an infiltration of new magma which erupts rapidly incorporating olivines along the way. The host melt also records processes of diffusive fractionation during groundmass crystallisation. Semi-volatile trace metals and Li have been found to behave in a volatile fashion at both Mt. Etna and Piton de la Fournaise. At Mt. Etna, CO2 gas fluxing may have been important for causing the transfer of Cu from magmas at depth, to magmas stored in the shallow plumbing system. At Piton de la Fournaise trace metals are not simply behaving as incompatible elements but rather show the influence S and H2O loss during degassing. However, when investigating trace metal concentrations in volcanic products this thesis shows that the affect of sulphide immiscibility should not be neglected. Loss of chalcophile trace metals to sulphide melts prevents partitioning of the element into a gas phase. Destabilisation of these melts on the other hand, may release enriched concentrations of trace metals to a gas phase.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available