The Caledonian orogen of East Greenland contains remnants of Archean, Paleoproterozoic, late Mesoproterozoic, and early Neoproterozoic rocks that occur within far-traveled thrust sheets, and bear witness to a complex polyorogenic history of the region prior to Caledonian orogenesis. Archean and Paleoproterozoic complexes consist mainly of granitoid orthogneisses. A succession of Paleoproterozoic tholeiitic metabasalts is present in some of the foreland windows. A major unit of late Meso-proterozoic metasedimentary rocks (Krummedal supracrustal sequence) contains early Neoproterozoic (ca. 950 Ma) as well as Caledonian granites. There is evidence for Archean (ca. 2800–2600 Ma), Paleoproterozoic (2000–1750 Ma), and late Grenvillian (ca. 950 Ma) deformation and metamorphism, but Caledonian overprinting complicates the study of these events. This paper presents a broad overview of the various rock units with structural, geochemical, and geochronologic data. The Paleoproterozoic metabasaltic rocks from the foreland windows are described in more detail.

Caledonian (435–425 Ma) and “Grenvillian” (950–900 Ma) S-type leucogranites and augen gneisses are prominent in the thrust units that form the southern half of the East Greenland Caledonian orogen, south of 76°N. Such rocks do not occur further north (76°N–81°N), where the bedrock is dominated by Paleoproterozoic orthogneisses and metagranitoid rocks (2000–1750 Ma). More mafic Caledonian granitoid rocks (quartz diorites, granodiorites, quartz monzonites, syenites, etc.) are found only in the southernmost parts of the orogen (∼71°N), side by side with S-type leucogranites. The S-type granites were formed by partial fusion of “fertile” lithologies within the late Mesoproterozoic Krummedal supracrustal sequence prior to or during emplacement of the thrust units and subsequent collapse of the orogen. The lack of similar granites north of 76°N is probably related to the absence of major units of metasedimentary rocks in that area. Among the granitoid rocks in the southernmost area, an early quartzdioritic to granodioritic intrusion was dated at 466 ± 9 Ma; this is ∼35 m.y. older than most Caledonian S-type granites. Quartzmonzonitic, granitic, and syenitic intrusions have yielded ages of 444–432 Ma. These rocks are geochemically similar to Caledonian granites in Scotland and may be related to subduction of oceanic lithosphere underneath East Greenland. The north-south variation in the occurrence of granites in the East Greenland Caledonides is the expression of an original (pre-thrusting) west-east zonation. It is envisaged that the orogen consists of a number of parallel belts, now telescoped by thrusting: a southeastern belt containing supracrustal rocks (Krummedal sequence) with leucogranites, with more mafic granitoids in the southeast, and a northwestern belt where these rocks do not occur. These belts are envisaged to run from Scotland over the southern parts of the East Greenland Caledonides and, obliquely to the Greenland coast, over the North-East Greenland shelf to Svalbard and Norway, where similar rock units also occur.

The Caledonian orogen of North-East Greenland hosts numerous mineral occurrences related to (1) pre-Caledonian crystalline complexes (Pb-Zn skarn type); (2) Neoproterozoic basins (strata-bound copper); (3) Caledonian granites (vein-type gold, silver, tungsten, arsenic, and antimony); and (4) late Caledonian extensional structures (vein base metal ± silver). Sr, Pb, and Sm-Nd isotope analyses of scheelite (CaWO 4 ) indicate a heterogeneous, probably local, source for tungsten, and Sr isotopic data support a genetic link to Caledonian magmatic activity. Pb isotopes indicate mixing of Pb derived from late waning-stage fluids from the granites and from interaction with wall rocks. Sm-Nd isotopic data for the investigated scheelites indicate that a portion of the rare earth elements was derived from fluids that had interacted with both Archean-Paleoproterozoic crystalline basement and Mesoproterozoic-Neoproterozoic sedimentary rocks. Mineral occurrences associated with fault zones and late Caledonian veins all show a genetic relationship with Caledonian granite emplacement. Sm-Nd isotopic data from scheelite define an errorchron with a slope corresponding to 382 ± 39 Ma (mean square of weighted deviates [MSWD] = 2.6) and an initial 143 Nd/ 144 Nd value of 0.511642 ± 0.000049. This indicates emplacement during the latest stages or even subsequent to emplacement of most Caledonian granites around 425 Ma. The initial Nd isotopic ratio defined by the scheelite Sm-Nd isotopic correlation line is identical within error to the values of S-type granitoids. The multi-isotope studies indicate that tungsten may have been deposited from fluids associated with Caledonian granites, which provided heat sources for local hydrothermal circulation cells. Forced into faults, thrusts, and fractures, the fluids were trapped by dominantly Ca-rich sediments.

In this review we summarize the major lithological and geochemical characteristics of the Mesoarchean (ca. 3075 Ma) Ivisaartoq greenstone belt, Nuuk region, southern West Greenland. In addition, the geological characteristics of the Ivisaartoq greenstone belt are compared with those of other Archean greenstone belts in the area. The Ivisaartoq greenstone belt is the largest Mesoarchean supracrustal lithotectonic assemblage in the Nuuk region. The belt contains well-preserved primary magmatic structures including pillow lavas, volcanic breccias, and cumulate (picrite) layers. It also includes variably deformed gabbroic to dioritic dikes, actinolite schists, serpentinites, siliciclastic sediments, and minor cherts. The Ivisaartoq rocks underwent at least two stages of postmagmatic metamorphic alteration, including seafloor hydrothermal alteration and syn- to post-tectonic calc-silicate metasomatism, between 3075 and 2961 Ma. The trace element systematics of the least altered rocks are consistent with a subduction zone geodynamic setting. On the basis of lithological similarities between the Ivisaartoq greenstone belt and Phanerozoic forearc/backarc ophiolites, and intra-oceanic island arcs, we suggest that the Ivisaartoq greenstone belt represents a relic of dismembered Mesoarchean suprasubduction zone oceanic crust. The Sm-Nd isotope system appears to have remained relatively undisturbed in picrites, tholeiitic pillow lavas, gabbros, and diorites. As a group, picrites have more depleted initial Nd isotopic signatures (ɛ Nd = +4.2 to +5.0) than gabbros, diorites, and tholeiitic basalts (ɛ Nd = +0.3 to +3.1), consistent with a strongly depleted mantle source. In some areas gabbros include up to 15 cm long white inclusions (xenoliths). These inclusions are composed primarily (>90%) of Ca-plagioclase and are interpreted as anorthositic cumulates of the lower oceanic crust brought to the surface by upwelling gabbroic magmas. Alternatively, the inclusions may represent the xenoliths from older (>3075 Ma) anorthositic crust onto which the Ivisaartoq magmas were emplaced as an autochthonous sequence. However, no geological evidence has been found for such older anorthositic crust in the region. The anorthositic cumulates have significantly higher initial ɛ Nd values (+4.8 to +6.0) than the surrounding gabbroic matrix (+2.3 to +2.8), suggesting two different mantle sources for these rocks.