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Delayed fractionation of basaltic lavas
Authors:Sven Maaløe  Rolf B Pedersen  D James
Institution:(1) Institutt for Geologi, Allégaten 41, 5007 Bergen, Norway;(2) Grant Institute of Geology, University of Edinburgh, West Mains Road, EH9 3JW Edinburg, Scotland
Abstract:The phenocryst cores of the basaltic lavas from Jan Mayen and Hawaii display a range in compositions. The textural features of the phenocrysts also vary, both euhedral and skeletal phenocrysts are present in the same thin section. Apparently the basaltic magmas underwent crystallization within a temperature interval of 50–200° C before they became fractionated. The fractionates of basaltic lavas are therefore average compositions of the phenocryst assemblages rather than liquidus compositions. This type of fractionation is called delayed fractionation. It is considered that most tholeiitic and alkalic basaltic lavas undergo delayed fractionation.
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