Volcanic geology of Thingmuli, Eastern Iceland

• Main Author: Carmichael, Ian Stuart Edward
• Published: Imperial College London 1962
• Subjects: 551.21
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602161

Part of a Tertiary central volcano in eastern Iceland has been mapped, and a stratigraphic succession has been established. This complex, which in the early stages shows a shield-like form, is built up predominantly of tholeiitic lavas, together with olivine-basalts, toleiitic-andesitcs, andesites and rhyodacites, and all gradations are found between these types. Acid intrusions are also found, together with an intense basic dyke swarm, and two sets of cone-sheets, an early basic and a later acid set. Superimposed upon the structure is an extensive zone of hydrothermal alteration; this alteration increases in intensity towards the centre of the complex, and the increase in intensity may be zoned by the amygdale minerals so prominent in many of the basic lavas. A selection of the lavas and intrusions which form the volcano have been examined petrographically and analysed chemically. There is a regular and continuous gradation in the composition of this series, which is unusually rich in iron. The genesis of this series is discussed.