Rit (Vísindafélag Íslendinga) - 01.06.1967, Side 52

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have not been located may be taken to indicate that the dip
of the lavas is rather due to sagging than tectonic tilting.
Trausti Einarsson: What would be the density of pillow
lavas, — will it be more than 2.2 g/cm3 which I have used
for “tuffs and breccias”?
H. Sigurdsson: Pillow lavas formed in deeper submarine
eruptions will not vesiculate due to a high hydrostatic load,
and hence their specific gravity might be expected to be simi-
lar to compact basalt lavas, i.e. of the order of 2.7.
Trausti Einarsson: The local gravity bowl in the North-
west-Peninsula indicates a light layer at a depth of 3—5 km
but this need not be sial.
G. Pálmason: Trausti Einarsson mentions a tectonic phase
when Iceland rose above the surrounding ocean floor and
that this phase might be connected with the formation of
the gravity anomaly. Could he elaborate a little more what
processes could conceivably have caused this uplift.
H. Sigurdsson: How can we assume that block faulting
caused both central thickening of a deep layer under the
Northwest-Peninsula and delineated the outlines of the pre-
sent gravity field?
Trausti Einarsson: Block faulting and uplift is a common
phenomenon. In the present case I assume that under in-
fluence of the stress field in which the fragile surface layers
were broken and faulted, deeper light layers moved plas-
tically and led to a central thickening which caused the main
Bouguer bowl and the uplift of the country. These light deep
layers need not be sial, they could be in part glassy basaltic
material.
7. Jónsson: Concerning the occurrence of acid volcanic
rocks in Iceland I would like to draw attention to a rather
big acidic area to the north of Hvammsfjördur, around Sael-
ingsdalur and Skeggjadalur. The geology of the Vestfirdir
is very little known but might be of great interest in this
connection.
H. Sigurdsson: G j á r or open fissures in the neovolcanic