Crustal thermal state and origin of silicic magma in Iceland: the case of Torfajökull, Ljósufjöll and Snæfellsjökull volcanoes

Pleistocene and Holocene peralkaline rhyolites from Torfajokull (South Iceland Volcanic Zone) and Ljosufjoll central volcanoes and trachytes from Snaefellsjokull (Snaefellsnes Volcanic Zone) allow the assessment of the mechanism for silicic magma genesis as a function of geographical location and cr...

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Bibliographic Details
Published in:Contributions to mineralogy and petrology 2007-05, Vol.153 (5), p.593-605
Main Authors: Martin, E., Sigmarsson, O.
Format: Article
Language:English
Subjects:
Crystallization
Fractionation
Holocene
Magma
Melting
Mineralogy
Petrology
Pleistocene
Rift zones
Volcanoes
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Summary:Pleistocene and Holocene peralkaline rhyolites from Torfajokull (South Iceland Volcanic Zone) and Ljosufjoll central volcanoes and trachytes from Snaefellsjokull (Snaefellsnes Volcanic Zone) allow the assessment of the mechanism for silicic magma genesis as a function of geographical location and crustal geothermal gradient. The low [delta]180[omicron] (2.4 0/00) and low Sr concentration (12.2 ppm) measured in Torfajokull rhyolites are best explained by partial melting of hydrated metabasaltic crust followed by major fractionation of feldspar. In contrast, very high 87Sr/86Sr (0.70473) and low Ba (8.7 ppm) and Sr (1.2 ppm) concentrations measured in Ljosufjoll silicic lavas are best explained by fractional crystallisation and subsequent 87Rb decay. Snaefellsjokull trachytes are also generated by fractional crystallisation, with less than 10% crustal assimilation, as inferred from their [delta]18O. The fact that silicic magmas within, or close to, the rift zone are principally generated by crustal melting whereas those from off-rift zones are better explained by fractional crystallisation clearly illustrates the controlling influence of the thermal state of the crust on silicic magma genesis in Iceland. [PUBLICATION ABSTRACT]
ISSN:0010-7999
1432-0967
DOI:10.1007/s00410-006-0165-5