Jökull - 01.01.2014, Blaðsíða 43

Magnetostratigraphy, K-AR dating and erosion history of Hafrafell, SE–Iceland
Figure 1. Geological setting of the Hafrafell research area (blue frame) in relation to the Öræfajökull volcano,
neighboring volcanic centers (VC) east of the accreting rift zone. – Jarðfræðilegar aðstæður Hafrafells (blár
ferningur) í útjaðri megineldstöðvarinnar í Öræfajökli ásamt nærliggjandi megineldstöðvum fyrir austan rek-
belti landsins.
finely grained, brown hyaloclasite grains with dark
gray to black, angular breccia fragments. We assume
the primary hyaloclastite to have been rapidly trans-
ported to site of deposition and remained mainly intact
thereafter. The laminated hyaloclastite is distinctly
bedded with rounded to subrounded rocks, normally
of variable lithology and color. We assume the lami-
nated sediment to have been reworked and subjected
to considerable transport from source. A total of 12
erosion surfaces, HR1 to HR12, were defined within
the Hafrafell strata.
Dikes and alteration
Numerous near-vertical dikes cut through Hafrafell
which, over a horizontal distance of some 1600 m,
amounted to 234 m or 14.7% at 120 m a.s.l. Mean
dike thickness is 2.5 m for 94 dikes. Mean dike
strike is N70◦E (22◦ s.d.). In addition a few near-
horizontal dike sheets/sills are observed at the south
end of Hafrafell. The intensity of dikes, sheets and
rhyolite intrusions increases generally toward north.
The south part of Hafrafell lies within the mesolite-
scolecite zeolite zone but some 2 km farther north
JÖKULL No. 64, 2014 43