The Petrology of Thingmuli, a Tertiary Volcano in Eastern Iceland |
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| Authors: | CARMICHAEL I S E |
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| Institution: | Department of Geology, Imperial College of Science London, S. W. 71 |
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| Abstract: | The Tertiary flood-basalt sequence of eastern Iceland is intermittentlydisturbed by central volcanic activity with the voluminous eruptionof acid magma. Associated with one of these central volcanoes,described in this paper, is an intense swarm of acid and basicdykes, a set of acid cone-sheets, and extensive superimposedhydrothermal alteration. The lavas and intrusions which makeup the volcano grade in composition from olivine-tholeiites,through olivine-free tholeiites, basaltic-andesites, and andesites(icelandites), to rhyolites. This series is unusually rich iniron, titanium, and manganese, and poor in magnesium; aluminaand total alkalis also tend to be low in the basic members.Magnetite (sensu lato) plays a varied role in the order of crystallization,and it is only in the intermediate stages of this fractionatedseries that magnetite is available for crystal fractionation.The otherwise progressive enrichment of iron relative to magnesiumthroughout the successive liquids of the series is halted duringan intermediate stage, as magnetite becomes an early-crystallizingphase. |
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