Age of fire

• Main Author: Muir-Wood, Robert
• Format: Book Part
• Language: English
• Published: Oxford University PressOxford 2024
• Subjects: Iceland
• Online Access: http://dx.doi.org/10.1093/oso/9780198871620.003.0003; https://academic.oup.com/book/chapter-pdf/58292257/oso-9780198871620-chapter-3.pdf

Abstract This chapter focuses on the volcanic processes that shaped the landmass of Britain between 60 and 57 million years ago. It considers the principles of magma chemistry, according to partial melting, fractional crystallization, and how the hot magma can melt the continental crust through which it passes. In a surface basaltic lava flow magma freezes quickly, and the grains stay small, whereas in a ‘gabbro’ or ‘granite’ the crystal size may be a centimetre or more in size when the magma cools slowly underground. In Iceland today, recent studies have consistently shown that vertical sheet dykes emerge from over-pressured magma chambers beneath volcanoes. Where a dyke breaks surface lava flows form. Around the Hebrides, gravity mapping reveals the volume of dense mantle derived magma that has accumulated under each volcano, with the largest concentration beneath two least investigated volcanoes to the west: Blackstones and St Kilda.