EAST GREENLAND CALEDONIDES
East Greenland Caledonides

Tony Higgins is the present contact person at GEUS for the Caledonides. The investigations have been carried out over an extended series of years, and a large group of Danish and international scientists have participated.

Setting
The East Greenland Caledonides extends for 1300 km between 70°N (Scoresby Sund) in the south and 82°N (Kronprins Christian Land) in the north. This N-S trending orogenic belt was created by the collision of the continents of Laurentia (North America and Greenland) and Baltica about 400-435 Ma ago. The subsequent opening of the North Atlantic Ocean disrupted the Caledonian orogenic belt, and fragments of the orogen are now found in the widely separated locations of Svalbard, Scandinavia and the NW British Isles. The orogen takes its name from Caledonia, the Latin name for northern Britain.

Early work
The earliest systematic geological investigations in the East Greenland Caledonides were undertaken during the long series of Danish geological expeditions to East Greenland led by Lauge Koch between 1926 and 1958. Work in the basement gneiss complexes by Helge Backlund and Emil Wegmann in the 1930s suggested that intense waves of Caledonian migmatisation and metasomatism had transformed a thick pile of metasediments into granites and gneisses. Wide-ranging geological mapping and aerial reconnaissance by John Haller and colleagues in the 1950s appeared to confirm this interpretation, and led to development of the 'stockwerke' concept of in situ orogenesis. Thrusts were recognised, but were thought not to have significant displacements. The granites and gneisses of the infrastructure were envisaged as of Caledonian origin, and separated by a zone of detachment from a less deformed metsedimentary suprastructure. The high grade metasediments appear to pass gradually upwards into the unmetamorphosed, very thick Neoproterozoic to Ordovician succession that forms spectacular outcrops in the fjord zone of central East Greenland (72∞–75∞N). After Lauge Koch's expeditions were brought to a close in 1958, John Haller continued compilation of a set of 1:250 000 map sheets covering the region 72∞–76∞N (Koch & Haller 1971), a set of structural maps at 1:500 000 covering the entire orogenic belt (Haller 1970), and a comprehensive book on the "Geology of the East Greenland Caledonides" (Haller 1971).

[Geological map of northern East Greenland, showing position of the Caledonian foreland windows in the western marginal thrust belt.]

[Spectacular coloured limestones and dolostones of the Eleonore Bay Supergroup.]

Survey work
In 1968 the then Geology Survey of Greenland (GGU) began geological mapping in the Scoresby Sund region (69∞–72∞N), as part of the Survey's 1:500 000 geological mapping project. This project was continued after the Geological Survey of Greenland and the Geological Survey of Denmark merged in 1995, and the set of 14 map sheets that cover all the land areas of Greenland was completed in 2004. [LINK TO 1:500 000 MAP SHEETS]. Five summers mapping (1968–1972) in the Caledonian orogenic belt as well as the post-Caledonian succession, led to publication of the 1:500 000 Scoresby Sund geological map sheet (Sheet 12) in 1984, as well as 16 geological maps at scale 1:100 000 [LINK TO 1:100 000 MAP SHEETS?]. Mapping of the gneiss complexes in the Scoresby Sund region, by Survey geologists accustomed to working in the Precambrian gneiss terrains of West Greenland, raised doubts as to some of the interpretations of Lauge Koch's expeditions. Geochronological studies confirmed these doubts, and demonstrated that the gneisses retained clear evidence of their Archaean history, as well as Caledonian reworking. Furthermore, isotopic evidence from granites emplaced into migmatitic sediments yielded c. 1000 Ma ages, suggesting that at least some of the metasedimentary rocks were older than the Neoproterozoic Eleonore Bay Supergroup. Two levels of thrust sheets were distinguished, and displacements in excess of 100 km were proposed, again a contrast to the limited thrust displacements previously proposed by John Haller and colleagues.

Minor follow-up work was carried out in the Kong Oscar Fjord region (72∞–75∞N) between 1976 and 1978, but the next major mapping project in the Caledonides was the 1988–1990 geological mapping of the Dove Bugt region (75∞–78∞N). This region is dominated by Palaeproterozoic gneiss complexes, which in the northern part of the region contain numerous eclogitic enclaves. Subsequent research has demonstrated that the eclogites are Caledonian, and form part of an eclogite province that extends 400 km farther northwards to Kronprins Christian Land. In Dronning Louise Land, in the western part of the Dove Bugt region, Survey work confirmed many of the observations made by the 1952–1954 British North Greenland expedition, but demonstrated that the Zebra Series quartzites locally contain Skolithos ichnofossils, and are therefore of early Cambrian in age. The Dove Bugt 1:500 000 map sheet was printed in 1997.

The next major project in the East Greenland Caledonides was in Lambert Land and Kronprins Christian Land (78°–81°N), where the border against the foreland to the west is well exposed. The transition to the foreland is formed by a thin-skinned fold and thrust belt developed in Ordovician–Silurian shelf carbonates. This fold and thrust belt is over-ridden in the east by the Vandredalen thrust sheet that largely comprises a thick succession of Proterozoic clastic rocks known as the Rivieradal Group. Farther east older Palaeoproterozoic–Mesoproterozoic quartzite sequences and interbedded volcanic rocks make up higher thrust sheets. Studies of colour alteration indices in conodonts from the carbonate rocks in the thin-skinned fold and thrust belt show that the former overburden (made up of thrust sheets now eroded) ranged from 4 km in the west to more than 12 km in the east). The Lambert Land 1:500 000 geological map sheet was printed in 2000.

[Cross-section of marginal thrust belt of Kronprins Christian Land showing overburden deduced from conodont alteration colours.]

The final segment of the Caledonian orogenic belt to be mapped by the Survey was the Kong Oscar Fjord region (72°–75°N), well known from the activities of Lauge Koch's expeditions, and the 1:250 000 geological maps of Koch & Haller (1970). The two year mapping project in the 1997–1998 field seasons produced many surprises, and resolved several of the outstanding problems of East Greenland Caledonian geology. Most notable was recognition of two major foreland windows, that provided convincing evidence for distinguishing two major thrust sheets above the windows; both thrust sheets have displacements probably in excess of 100 km. These conclusions completely undermine the arguments for in situ Caledonian orogenesis and limited thrust displacements, implicit in Haller's (1971) 'stockwerke' concept. The focus of orogenic activity was probably several hundred kilometres offshore the present coast of East Greenland. Within the thrust sheets, extensive ion probe studies of detrital zircons in the high grade metasediments, and in the granites hosted by the metasedimentary succession, provide insights into the make-up of the Laurentian craton prior to Caledonian orogenesis. The high grade metasedimentary rocks were laid down after 1050 Ma (the oldest detrital zircons) and prior to emplacement of a suite of 940–910 Ma S-type augen granites. A later suite of Caledonian granites, also produced by melting of metasediments, has yielded a narrow range of ages from 435–425 Ma. Comparable metasedimentary successions containing similar types of early Neoproterozoic and Caledonian granites are also known in Svalbard and NW Scotland, providing further evidence of the proximity of these terrains prior to opening of the North Atlantic.

[Cross-section of the Eleonore Sø and Målebjerg windows, with thrust sheet structure and nomenclature shown in legend.]

[Early Cambrian quartzites of the Slottet Formation (SF) and clastic sediments and volcanic rocks of the Eleonore Sø complex, in the Eleonore Sø window. These units are not represented in the overlying thrust sheets.]

[The Målebjerg window. Gneisses (G) and early Cambrian quartzites of the Slottet Formation (SF), overlain by metasediments of the Niggli Spids thrust sheet (NSTS). The Niggli Spids thrust (NST) has a westward displacement of more than 100 km.]

Synthesis
The Survey's regional mapping of the East Greenland Caledonides has extended over a period of 30 years, with major mapping activity in 13 field seasons with extensive helicopter support. Each season some 13–15 field teams have been active in the field, the geologists involved coming partly from the Survey, but including large numbers of specialist guests from geological institutes and Surveys mainly in Denmark, Britain, Australia and the USA. The final field season in 1998 was followed by printing of the Kong Oscar Fjord 1:500 000 map sheet in 2001, completing the set of four map sheets that cover almost the entire orogen. Using these map sheets as a basis, a new map sheet of the orogen at a scale of 1:1 million was compiled, and printed in 2003. Many of the geologists involved in the original field mapping are at present cooperating in the production of a synthesis volume on the East Greenland Caledonides, which is planned to be published by the Geological Society of America in their Memoir or Special Paper series, probably in 2006.

[Portraits]

Niels Henriksen. Retired former head of Geological Mapping Department. Emeritus Senior Research Geologist Feiko Kalsbeek. Retired Petrologist and geochronologist. Emeritus Senior Research Geologist.

A.K. (Tony) Higgins. Structural geologist. Senior Research Geologist

Selected References:
Brueckner, H.K., Gilotti, J.A. & Nutman, A.P. 1998. Caledonian eclogite-facies metamorphism of Early Proterozoic protoliths from the North-East Greenland eclogite province. Contributions to Mineralogy and Petrology, 130 , 103–120.

Gilotti, J.A. & Ravna, E.J.K. 2002. First evidence for ultrahigh-pressure metamorphism in the North-East Greenland Caledonides. Geology 30 , 551–554.

Haller, J. 1970: Tectonic map of East Greenland (1:500,000). An account of tectonism, plutonism and volcanism in East Greenland. Meddelelser om Grønland 171 (5), 286 pp.

Haller, J. 1971. Geology of the East Greenland Caledonides. Interscience, London, 413 pp.

Higgins, A.K. & Leslie, A.G. 2000. Restoring thrusting in the East Greenland Caledonides. Geology 28 , 1019–1022.

Higgins, A.K., Leslie, A.G. & Smith, M.P. 2001a: Neoproterozoic – Lower Palaeozoic stratigraphical relationships in the marginal thin-skinned thrust belt of the East Greenland Caledonides: comparisons with the foreland in Scotland. Geological Magazine 138 , 143–160.

Higgins, A.K. et al. 2004: The foreland-propagating thrust architecture of the East Greenland Caledonides 72°–75°N. Journal of the Geological Society (London) 161 (in press)

Kalsbeek, F., Jepsen, H.F. & Nutman, A.P. 2001a. From source migmatites to plutons: tracking the origin of c. 435 Ma granites in the East Greenland Caledonian orogen. Lithos, 57 , 1–21.

Kalsbeek, F., Jepsen, H.F. & Jones, K.A. 2001b. Geochemistry and petrogenesis of S-type granites in the East Greenland Caledonides. Lithos, 57 , 91–109.

Koch, L. & Haller, J. 1971: Geological map of East Greenland 72°-76° N. Lat. (1:250,000). Meddelelser om Grønland 183 , 26 pp. (+ 13 map sheets).