Evolution of Icelandic Central Volcanoes: Evidence from the Austurhorn Plutonic and Vestmannaeyjar Volcanic Complexes
WOODS HOLE OCEANOGRAPHIC INSTITUTION MA
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There are several aspects of Icelandic magmatism which are not predicted from its geographic position along the mid-Atlantic Ridge. Specifically, local occurrences of alkalic lavas and oversaturated silicic magmas are uncommon in a mid-ocean ridge setting. This study uses field, petrologic and geochemical data to understand the petrogenesis of these diverse lava types. Two areas have been investigated the volcanic Vestmannaeyjar archipelago and the hypabyssal Austurhorn intrusive complex. Vestmannaeyjar is located at the tip of a transgressive ridge segment the eastern neovolcanic zone the most recent eruption in this area was Eldfell in 1973. Austurhorn is an evolved central volcano in southeastern Iceland which was active approximately 607 Ma and has been exhumed by glaciation. In both areas, the relative contributions of fractional crystallization and crustal melting to geochemical trends among cogenetic magmas have been assessed, and fractionation processes are found to dominate. Vestmannaeyjar moderate pressureapprox. 8 kbar fractionation of mantle-derived liquids can produce the observed range of erupted compositions. Radiogenic and stable isotope data support this scenario. At Austurhorn sampled mafic and felsic magmas differentiated at near surface conditions approx. 2 kbars. The cumulus mineralogy of associated gabbros supports this model.
- Physical and Dynamic Oceanography
- Geology, Geochemistry and Mineralogy