The Major Intrusions of South-Eastern Iceland

Abstract

The intrusions of plutonic habit in Iceland have their greatest development in the south-east of the country, and our present knowledge of them is summarized by Thoroddsen, who gives the location of the main occurrences (VII, pp. 264–87). Beyond this little is known of the relationship of the intrusions to the country- rocks or their petrological character; there is one short paper by Helland dating from 1884 (V). The present study is the result of four summer field excursions by the second-named author, and one excursion by his collaborators, who are responsible for the section on the Slaufrudal stock only. Some intrusions have been mapped on the ‘Generalstabens Topografiske Kort’ (1: 50,000) ; but this map is not yet completed, and more detailed work on certain areas is on that account held up. The country-rocks are mainly plateau-basalts of Tertiary age, with some rhyolitic lavas, tuffs, and breccias, having a north-westward to west-north-westward dip of 5° to 20°, and cut by numerous dyke-intrusions of a regional north-easterly to north-north-easterly trend. Some of the gabbros are beneath the Vatna Jökull ice-cap, and are represented by pebbles in the southern outwash fans. The outcrops of the rocks here described are indicated on the sketch-map (fig. 1, p. 506).