Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.792345
Title: Complex petrogenesis of Lesser Antilles arc lavas : insights from mineral chemistry
Author: Johnson, Hannah Margaret
ISNI:       0000 0004 8498 3103
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 2015
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Abstract:
The Lesser Antilles arc is unusual in erupting high MgO lavas relative to many other volcanic arcs. This provides a rare opportunity to study early fractionating phases, such as olivine, with the aim of gaining insight into the early petrogenesis of these lavas as well as shallow level magmatic interactions and storage. Olivine, plagioclase and clinopyroxene crystals were studied from the central (Guadeloupe and Dominica) and southern (St. Vincent, Bequia, Petite Martinique, Carriacou and Grenada) islands of the arc in order to assess how deep (melting and source processes) and shallow (fractional crystallisation, crustal contamination and magma mixing) processes varied along arc strike. Analysis of mineral crystals from the Lesser Antilles has shown significant variation in both textural and chemical signatures in crystal cargoes from the same lava. Multiple populations are observed in host lavas along the arc. Geothermobarometric modelling showed the southern arc clinopyroxenes to have crystallised at higher temperatures and pressures (with the exception of the Bequia crystals) than those from further north. High forsterite olivines (up to Fo91) and high anorthite plagioclases (up to An96) indicate water is required in the melts, particularly in the south of the arc. Bimodal CaO, Al2O3, Cr, Y, Yb and in some cases Sc contents in the olivines suggest the disaggregation of cumulate xenoliths before assimilation into the host melts. Assimilation and magma mixing are also apparent in the plagioclase crystals, as are varying rates of ascent through the magmatic plumbing system. Effects of shallow level degassing or decompression are visible in the plagioclases and these processes could also be a suitable method for generating bimodal forsterite contents in the olivines from one Guadeloupe host lava. Processes identified from the mineral phases show that petrogenesis in the Lesser Antilles is complex and varies along arc strike, with the southern islands potentially requiring more water in the melts and deeper crystallisation depths. In general, deeper processes are more prevalent to the south of the arc, with shallower processes dominating the north and centre.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.792345  DOI: Not available
Keywords: Geochemistry ; Olivine ; Plagioclase ; Clinopyroxene ; LA-ICP-MS
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