McGarvie, D. W. and Burgess, R. and Tindle, A. G. and Tuffen, Hugh and Stevenson, John A. (2006) Pleistocene rhyolitic volcanism at Torfajökull, Iceland : eruption ages, glaciovolcanism, and geochemical evolution. JÖKULL, 56. pp. 57-75. ISSN 0449-0576Full text not available from this repository.
The Torfajökull central volcano lies in Iceland’s southern flank zone (a non-rifting zone) and last erupted in the 15th century. Peralkaline rhyolites from its pre-Holocene formations have been dated by the Ar-Ar method. Ages from 67±9 ka to 384±20 ka indicate Pleistocene eruptions, with the oldest age (384 ka) also being from the most evolved rhyolite (a pantellerite). The oldest age indicates that a mature and evolved magmatic-volcanic system was well established by the mid-Pleistocene and that the central volcano has been active for at least 400 ka. Good correlation is found between the Ar-Ar ages of sustained rhyolite eruptions into ice sheets (i.e. rhyolite tuya formation) and oxygen isotope stages dominated by cold conditions. This is the first stage of developing a new proxy that uses rhyolitic glaciovolcanic edifices to provide estimates of past Icelandic ice sheet thicknesses. The geochemistry of the dated samples corroborates earlier work showing a simple but enigmatic trend of steadily-decreasing alkalinity towards the present (i.e. older rocks are more evolved). The new ages reveal a hitherto-unrecognised drop in rhyolite alkalinity after 83 ka, which may be linked to the evacuation of c. 16 km3 of rhyolite during a subglacial eruption into the last (Weichselian) ice sheet, for which two new and overlapping Ar-Ar ages of 67±9 ka and 72±7 ka have been obtained. This rhyolite eruption, which is the largest known from Torfajökull, heralded a major change in the magma system as all subsequent eruptions are of small volume (<0.3 km3), dominated by subalkaline compositions, and characterised by interactions with mafic magmas. This change may be linked to lower rhyolite magma replenishment rates and/or to the increasing influence of rift zone volcano-tectonics.
|Journal or Publication Title:||JÖKULL|
|Uncontrolled Keywords:||Torfajokull rhyolite obsidian subglacial eruption Pleistocene glaciovolcanism Iceland|
|Subjects:||G Geography. Anthropology. Recreation > GE Environmental Sciences|
|Departments:||Faculty of Science and Technology > Lancaster Environment Centre|
|Deposited By:||Dr Hugh Tuffen|
|Deposited On:||07 Oct 2009 13:04|
|Last Modified:||07 Jan 2015 14:05|
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