Large-volume lateral magma transport from the Mull volcano: An insight to magma chamber processes

Abstract

Long-distance lateral magma transport within the crust has been inferred for various magmatic systems including oceanic island volcanoes, mid-oceanic ridges, and large igneous provinces. However, studying the physical and chemical properties of active fissure systems is difficult. Hence, this study investigates the movement of magma away from the Mull volcano in the North Atlantic Igneous Province, where erosion has exposed its upper crustal dike networks. Magmatic lineations within dikes indicate that the magma flow in the Mull dike suite changed from near vertical to horizontal within 30 km of the volcanic center. This implies that distal dikes were fed by lateral magma transport from Mull. Geochemical characteristics indicate that many <50 km long dikes have deep crustal signatures, reflecting storage and assimilation in Lewisian basement. Following crystallization and assimilation in the lower crust, magma fed an upper crustal reservoir, where further fractionation and incorporation of Moinian rocks generated felsic compositions. Distal dikes are andesitic and reflect events in which large volumes of mafic and felsic magma were combined by mixing between lower and upper crustal reservoirs to generate the 30–80 km3 required to supply the long-distance dikes. Once propagated, compositions along dikes were not significantly affected by assimilation and crystallization. Supplying the distal dikes with magma would have required a large-scale evacuation of the crustal reservoirs that acted as a potential trigger for explosive volcanism and the caldera formation recorded in Mull central complex.

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ORCID for Rex N. Taylor: orcid.org/0000-0002-9367-0294

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