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Geochemical and Field Relationships of Pillow and Dike Units in a Subglacial Pillow Unit Undirhliđar Quarry, Southwest Iceland

By Lindsey J. Bowman


Undirhlíðar quarry is located on the Sveifluhals ridge, a Pleistocene subglacial pillow ridge within the NE-SW trending Krísuvík fissure swarm on the Reykjanes peninsula in Southwest Iceland. The walls of Undirhlíðar quarry provide excellent exposures of the internal architecture of the pillow ridge, yielding insights into the sequence of eruptive and intrusive events that construct subglacial ridges. In particular, the south and east walls expose at least 5 different pillow units and 3 dikes. Also seen in the east wall is a black, glassy breccia unit that appears on both the north and south sections of the east wall. Preliminary investigations of the west wall reveal a sixth pillow unit. The units can be separated into two groups primarily based on the presence or absence of olivine. Trace element variations also reveal two groups, but the geochemical groups do not correspond exactly to the mineralogical groups. This is consistent with the findings of Alcorn (2011), who focused on the south wall. Within each geochemical group, compositional variations can be explained by various additions or subtractions of plagioclase, clinopyroxene and olivine. Based on mineralogical, geochemical, and field relationships, a model reconstructing the order of the events for the pillow ridge is proposed. This model suggests early effusive activity occurred over multiple eruptive events and was followed by an explosive phase that preceded another effusive sequence. This contrasts with the current model for subglacial eruptions, which suggests a single effusive phase transitions into explosive activity

Topics: iceland, subglacial volcanism, basalt, geochemistry, Geology, Cosmochemistry
Publisher: Open Works
Year: 2012
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