Tectonic map of East Greenland (1:500,000). An account of tectonism, plutonism, and volcanism in East Greenland

Abstract

Greenland is bounded to the north and east by Paleozoic orogenic belts. The East Greenland fold belt, part of the circum-Scandic Caledonian domain, runs parallel to the coast line and is exposed from 70° to 82° N. Map sheets 1- 3 cover the belt and adjoining foreland parts north of the 72nd parallel, i.e. over a length of 1,100 km.

In Northeast Greenland, there are relics of a north-northwesterly trending Precambrian fold belt, the CAROLINIDES. This orogeny followed the deposition of the Precambrian Thule Group, that then covered most of North Greenland. Throughout late Precambrian and Lower Paleozoic times, the Carolinidian belt remained a positive element separating the geosyncline of Central East Greenland from smaller depositional basins in Northeast Greenland. The latter included the late Precambrian Hagen Fjord Group and a marine succession of Cambro–Silurian age.

In the geosyncline of Central East Greenland, more than 16,000 m of beds accumulated, some 13,000 m in the late (?) Precambrian (Eleonore Bay Group, Tillite Group) and 3,000 m in Cambro–Ordovician times.

The East Greenland CALEDONIDES developed during three distinct periods of tectonic activity which formed an unbroken sequence in the orogenic cycle: The main orogeny (old Caledonian), caused by deep-seated mobility, occurred in the late Silurian and/or earliest Devonian and affected the whole length of the east coast north of the 70th parallel. In Northeast Greenland, a marginal thrust belt outlines the ·western edge of this principal structure pattern. Regional metamorphism and igneous activity were most intense in the region between lats. 70° and 76°, i.e. the realm of the Central East Greenland geosyncline. This region also became the site of all late orogenic activity (young Caledonian), including the formation of an intramontane molasse basin (more than 7,000 m of Middle and Upper Devonian red beds).

In those highlands minor folding and thrusting lasted until the Lower Carboniferous. In the northern part of the Caledonian belt, tectonic unrest ended much earlier and incursions of the sea began in Carboniferous time (Moscovian). In the southern region, which was then still the site of continental deposition, elastic beds of Upper Carboniferous and Lower Permian age accumulated in fault-bounded troughs indicating a compound rift system.

The western flank of this late Paleozoic rift system remained henceforth positive and, therefore, part of the continent. But the area to the east subsided to become part of the Upper Permian Sea. This incursion re-stablished the marine regime over wide areas that had been land since the Caledonian mountains emerged. A fluctuating shelf-sea persisted there throughout the Mesozoic. The basement underlying this shelf gradually was broken off into a complex pattern of antithetic fault blocks.

Northerly running fault block structures characterize all of the coast north of Scoresby Sund (70° N). To the south, however, the coastal structure is quite different and also of later date. There, some 7,000 m of basalt lavas (Brito-Arctic province) erupted after Central East Greenland had become the site of regional upwarping at the very end of the Mesozoic. Except for a few flows, all lavas cooled on dry land. The building up of the basalt plateau was accompanied by gentle subsidence, and when the major volcanicity ceased, the plateau sank below sea-level. In Neogene times, differential vertical displacement then caused the present inland area to rise (resulting in the highest mountains in Greenland, viz. up to 3,700 m around the 69th parallel), while in the coastal area the plateau was submerged in the Denmark Strait. Between these areas of opposed displacement the Paleogene lava pile was bent into a giant flexure. Although this crustal warp (of some 8 km relative vertical displacement) has no direct bearing on the structures exposed on the mainland farther north, it is vital to the understanding of Greenland's southeast coast and, moreover, provides a link to the structural history of Iceland and the North Atlantic.