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Remobilization of Andesite Magma by Intrusion of Mafic Magma at the Soufriere Hills Volcano, Montserrat, West Indies |
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| Authors: | MURPHY M D; SPARKS R S J; BARCLAY J; CARROLL M R; BREWER T S |
| Institution: | 1DEPARTMENT OF EARTH SCIENCES, UNIVERSITY OF BRISTOL, WILLS MEMORIAL BUILDING, QUEENS ROAD, BRISTOL BS8 1RJ, UK 2DÉPARTEMENT DE MINÉRALOGIE, UNIVERSITÉ DE GENÈVE, 13 RUE DES MARAICHERS, 1211 GENEVA 4, SWITZERLAND 3DIPARTIMENTO DI SCIENZE DELLA TERRA, UNIVERSITÁ DI CAMERINO, 62032 CAMERINO, ITALY 4GEOLOGY DEPARTMENT, UNIVERSITY OF LEICESTER, UNIVERSITY ROAD, LEICESTER LE1 7RH, UK |
| Abstract: | The 1995–1999 eruption of the Soufriere Hills volcano,Montserrat, has produced a crystal-rich andesite containingquench-textured mafic inclusions, which show evidence of havingbeen molten when incorporated into the host magma. Individualcrystals in the andesite record diverse histories. Amphibolephenocrysts vary from pristine and unaltered to strongly oxidizedand pseudomorphed by anhydrous reaction products. Plagioclasephenocrysts are commonly reverse zoned, often with dusty sievetextures. Reverse zoned rims are also common on orthopyroxenephenocrysts. Pyroxene geothermometry gives an average temperatureof 858 ± 20°C for orthopyroxene phenocryst cores,whereas reverse zoned rims record temperatures from about 880to 1050°C. The heterogeneity in mineral rim compositions,zoning patterns and textures is interpreted as reflecting non-uniformreheating and remobilization of the resident magma body by intrusionof hotter mafic magma. Convective remobilization results inmixing together of phenocrysts that have experienced differentthermal histories, depending on proximity to the intruding maficmagma. The low temperature and high crystallinity are interpretedas reflecting the presence of a cool, highly crystalline magmabody beneath the Soufriere Hills volcano. The petrological observations,in combination with data on seismicity, extrusion rate and SO2fluxes, indicate that the current eruption was triggered byrecent influx of hot mafic magma. KEY WORDS: Montserrat; eruption; magma mixing; mafic inclusion; sieve texture |
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