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Contrasting conditions of rift and off‐rift silicic magma origin on Iceland
Author(s) -
Schattel Nadine,
Portnyagin Maxim,
Golowin Roman,
Hoernle Kaj,
Bindeman Ilya
Publication year - 2014
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2014gl060780
Subject(s) - rift , geology , silicic , crust , rhyolite , magma , rift zone , geochemistry , volcano , mineral redox buffer , east african rift , magma chamber , volcanic rock , mantle (geology) , tectonics , seismology
Abstract Factors controlling the origin of silicic magmas on Iceland are poorly constrained. Here we present new data on H 2 O content, pressure, temperature, oxygen fugacity, and oxygen isotope composition of rhyolites from Askja, Öræfajökull, and Hekla volcanoes. All these parameters correlate with tectonic (rift and off‐rift) setting of the volcanoes. Askja rift rhyolites originate through extensive assimilation of high‐temperature hydrothermally altered crust ( δ 18 O < 2‰) at shallow depths (≥1.8 km). These rhyolites are hot (935–1008°C), relatively dry (H 2 O < 2.7 wt%), and oxidized (QFM = +1.4). Cooler (874–902°C), wet (H 2 O = 4‐6.3 wt%), and non‐oxidized (~QFM to QFM‐1) off‐rift rhyolites (Öræfajökull, Hekla) originate through differentiation deeper in the crust (≥4 km) with almost no or little assimilation of high‐T, altered crust, as reflected by slightly lower to normal δ 18 O values (5.2–6‰). Although off‐rift rhyolites predominate during the Holocene, older silicic rocks on Iceland primarily formed in a rift setting possibly analogous to the oldest continental crust on Earth.