Melt inclusions from the Southwest Indian Ridge and Reykjanes Ridge : insights into melt extraction and magma chamber processes

• Main Author: Font Morales, Laura
• Format: Thesis
• Language: English
• Published: University of Southampton 2003
• Subjects: Indian; Reykjanes; Iceland
• Online Access: https://eprints.soton.ac.uk/465057/; https://eprints.soton.ac.uk/465057/1/906250.pdf

Naturally glassy melt inclusions trapped in olivine, plagioclase and pyroxene crystals in basalts from the Southwest Indian Ridge (SWIR) (49 o E-69 o E) and the Reykjanes (RR) (57 o N-63 o N) are used to study the diversity in composition of primary melts, the conditions of mantle melting, source composition and magma chamber processes occurring beneath these slow spreading ridges. The SWIR is characterised by cold mantle and low degrees of melting and the RR is characterised by high degrees of the Iceland mantle plume. The different geological mantle conditions of the SWIR and RR influence the composition of the melt inclusions. Along the SWIR, there is an increasing diversity in Mg# from east to west (69 o E-49 o E), between the glasses of olivine hosted melt inclusions with the plagioclase hosted melt inclusions. This suggests an entrapment of primitive melts in plagioclase phenocrysts and more evolved melts within late olivine crystals, which are close in composition to the matrix glasses. The eastern-most melt inclusions show high concentrations in incompatible elements (P, K, Ti, Na, (La/Sm), Zr/Y, Ba/Yb) , which decrease towards the western part of the ridge studied area. This suggests low degrees of melting in the eastern part, increasing towards the west. The variable fractionation histories between the melt inclusions and the matrix glass along the SWIR, and slight increase in the degree of melting from east to west suggest that the melts in the eastern side of the ridge migrated more slowly upwards from the mantle while fractionating en route compared to the melts in the western area. Once in the magma chamber, residence times were short prior to eruption, allowing little opportunity from different melt batches to mix and differentiate.