Háskóli Íslands

The Geldingadalahraun lava has a porphyritic texture, it contains, in order of decreasing abundance, the following minerals: plagioclase > olivine > clinopyroxene > spinel (Figure 1). It has an olivine tholeiite composition with Mg#=60.1. The bulk rock measurements lie at the primitive end of the spectrum of magmas that have erupted on the Peninsula over the Holocene.

Preliminary geothermobarometric calculations suggest a magma temperature of 1180-1190 °C on the surface. Furthermore, microphenocrysts of plagioclase, augite and olivine (Figure 1) crystallized in equilibrium with the basaltic glass in the shallow dyke, in accordance with geophysical observations. The bulk magma itself on the other hand is probably derived from a significantly larger depth (as deep as the crust-mantle boundary), suggesting that the shallow dyke is fed from a much deeper magma storage zone.

Full report on the major element composition of the rock and mineral samples are available here

Trace element and isotopic characterization are coming soon!

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