Melrakkaslétta, NE-Iceland: Volcanic lineaments and petrology

• Main Author: Sigurlaug María Hreinsdóttir 1985-
• Other Authors: Háskóli Íslands
• Format: Thesis
• Language: English
• Published: 2014
• Subjects: Jarðfræði; Bergfræði; Melrakkaslétta; Afrétt; Blikalónsdalur; Hraunhafnartangi; Iceland
• Online Access: http://hdl.handle.net/1946/18557

Mineralogical and geochemical analysis of 67 basalt samples from Melrakkaslétta reveals three rock types: a) Tholeiitic basalts in the early Quaternary volcanic lineaments along the east coast of the peninsula and the dolerite lava fields covering the central peninsula. b) Evolved high phosphorus basalts with strong Fe-Ti affinities occurring locally in the SE-part and c) olivine tholeiites along the west coast. The tholeiites contain occasional large xenocrysts of bytownite in plagioclase-clinopyroxene groundmass with abundant Fe-Ti oxides. The olivine tholeiite contains large phenocrysts of olivine dispersed in a groundmass of olivine, plagioclase, late clinopyroxene and Fe-Ti oxides. Formation of Melrakkaslétta during the earliest Quaternary followed a northwards rift-propagation of an inland volcanic lineament with a N fracture orientation (160-59°) (Hjartardóttir et al., 2014) that defines the present SE-coast of the peninsula. During the Quaternary, younger parallel volcanic lineaments formed on the rift side (west) of earlier lineaments. The Fjallgarðar lineament reaches as far north as the Afrétt while at least one younger lineament, now mostly covered by dolerite lavas, probably reached as far north as Hraunhafnartangi. Blikalónsdalur, a recent graben along the central peninsula, is parallel to the earlier tectonic lineaments. A productive volcanic lineament formed during the last glaciation along the west coast of the peninsula. This lineament is characterized by olivine tholeiites matching the composition of the off-shore volcanism. This youngest volcanic lineament with a NNW fracture orientation (110-159°) (Hjartardóttir et al., 2014) is subparallel to all other volcanic structures of the peninsula and its south-termination is connected to the junction of the rift-zone and the GOR that runs into Melrakkaslétta in Núpasveit. Safnað var 67 bergsýnum á Melrakkasléttu til greiningar á textúr og efnasamsetningu bergs og steinda. Þrjár berggerðir eru á Melrakkasléttu: a) þóleiítbasalt, ríkjandi í ...