Um dýpdarboringina í Vestmanna og í Lopra Scientific deep drilling in the Faeroes

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Published Dec 27, 2022
Arne Noe-Nygaard Jóannes Rasmussen

Abstract

A 1:50.000 geological map of the Faeroe Islands was published in 1969 with a shortened English edition in 1970. It was based on strictly chronostratigraphic principles. A total sequence of 3 km of tholeiitic basalt lavas was divided into a lower basalt series (about 900 m); a coal bearing sediment series (alout 10—15 m); a middle basalt series (about 1250 m) initiated by explosive volcanism producing agglomerates and tuffs, the tuffagglomerate zone; and an upper basalt series (about 675 m). Minor intrusions occur in form of dikes, sills and irregular intrusive bodies. The plateau has a low-angle easterly dip and the lavas of the lower basalt series are updomed in two areas, Vágar—Mykines and Suðuroy.

Geological and geophysical investigations were continued out on the shelf around the islands and on the Faeroe bank, Bill Baily bank and Lousy bank to the west.

Further geological information was obtained from two bore holes, one drilled in the summer 1980 at Vestmanna on Streymoy and the second in the summer and autumn of 1981 near the village of Lopra on Suðuroy (Fig- !)•

The faeroese government organized, and was economically responsible for the drill project, which was carried out in collaboration with the Geological Survey of Denmark. The drilling work was entrusted to the icelandic »National Energy Authority« (Orkustofnun). The drilling project was supported by the Carlsberg Foundation because of its scientific significance,
The bore hole at Vestmanna was drilled to determine if the lower basalt series and the coal bearing sediment series from Vágar could be traced down dip below sea level as far east as Streymoy, and to get information on the regional thermal gradient.

The bore hoie at Vestmanna (Fig. 2) was drilled from just above sea level with full core to a depth of 660 m (Fig. 3). The coal bearing sedimentary series from Vágar was found at 556 m. Here it was 3 m thick and contained basaltic sand and pebbles, but not coal. The tuff-agglomerate zone did not occur at the drill site in Vestmanna. The drilling continued 101 m into the upper part of the lower basalt series. The thermal gradíent was 40°C/km.

The Lopra bore hole was planned to penetrate at least 2 km into the unknown sequence below the known part of the lower basalt series and to obtain further thermal gradient data. The drill site was located west of the village Lopra a few m above sea
level, as low in the known part of the lower basalt series as possible (Fig. 4). A section through the bore hole reaching 2178 m below sea level is shown on Fig. 5. Six cores were taken (one core lost) at different levels and cuttings collected for each two m drilled. The drilled sequence consist of about 120 subaerially erupted lava flows indicating a subsidence of more than 2000 m. The lava flows average about 20 m in thickness while the intercalated sediments are up to 5 m. The drilled sequence consists of
aphyric to feldsparphyric tholeiitic basalts and must be considered as a continuation af the lower basalt series. The thickness of the total lava pile on the Faeroes is therefore at least 5 km and the early Tertiary basalt plateau on the European side of the North Atlantic, the Faeroe Islands, then reaches a thickness which is directly comparable with that on the East Greenland side of that ocean. The thermal gradient was about the samt as in Vestmanna.

Final scientific results will be published in Fróðskaparrit (supplementa) in 2 years.

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Section
Natural Sciences