Caledonian Nappes Research Articles

The Caledonian nappes of Kronprins Christian Land, eastern North Greenland

The earliest geological reconnaissance work in Kronprins Christian Land concerned with the Caledonian nappes was that of Nielsen (1941). Subsequently, Fränkl (1954, 1955) published maps of selected areas and a greatly simplified map of the central part of Kronprins Christian Land between Marmorvigen, Centrum Sø, and Romer Sø (fig. 4). Haller (1970, 1971) studied Kronprins Christian Land from the air as part of a larger operation in East Greenland. His conclusions concerning the nappes followed the work of Fränkl (1954, 1955). The primary aims of the 1980 field season were to remap the clastic sediments contained on the Caledonian nappes, to establish a detailed stratigraphy on each nappe and to correlate between each nappe and the platform sediments.

Lower Palaeozoic stratigraphy around Danmark Fjord, eastern North Greenland

Geologieal fieldwork in the Caledonian foreland of eastern North Greenland commenced during 1979 (Peel, 1980) was continued in 1980 with systematic regional mapping on a 1:100000 photomosaie base of western Kronprins Christian Land, from Centrum Sø in the south to Prins Frederik Øer in the north (fig. 6). Mapping was coneentrated on the essentially autochthonous sequence adjacent to Danmark Fjord, with Hurst & McKerrow (this report) investigating the Caledonian Nappe sequenee further to the east (Map i). In addition to activities in Kronprins Christian Land, short visits were also made to Kap Holbæk and Valdemar Glückstadt Land, on the western side af Danmark Fjord.

The Caledonian nappes of eastern North Greenland

Reconnaissance work in Kronprins Christian Land1–7 indicated the presence of one main nappe of late Proterozoic sediments2,3 thrust over Lower Palaeozoic platform carbonates similar to Peary Land7,8. Our 2-month helicopter-supported work in 1980 now indicates the presence of three thrust-bounded nappes. The Finderup Land Nappes, which occur in northern Kronprins Christian Land, contain a late Precambrian early Cambrian sequence in thrust contact above Silurian carbonates. The younger Vandredalen Nappe in thrust contact above the Finderup Land Nappes and Silurian carbonates occurs throughout Kronprins Christian Land and contains a thick sequence of late Proterozoic elastics and carbonates. In southern Kronprins Christian Land the Saefaxi Elv Nappe only contains Ordovician-?Silurian carbonates and is in thrust contact below Vandredalen Nappe. The nappes were involved in westward-directed thrusting (≥150 km) and are probably a result of continental collision when the northern part of lapetus Ocean closed in the late Silurian.

Subduction of the Iapetus Ocean crust beneath the Møre Gneiss Region, southern Norway

Basement–cover relations between Caledonian nappes and underlying Precambrian basement along the western coastline of southern Norway have long intrigued geologists and considerable progress has recently been made in understanding the Caledonian geology1–3, geochronological studies proving particularly useful. For example, the Precambrian gneisses along the coast from Bergen to Namsos yield ages up to 1,700 Myr, supposedly the age both of the formation of the rocks and the main metamorphism and deformation phases4. The Lofoten–Tromso archipelago is a presumed continuation of this basement block once sandwiched between the Caledonides of Norway and Greenland. An important phase of rock formation and metamorphism affected the gneisses here at around 1,800 Myr, whereas subsequent orogenies at 1,100 and 400 Myr (Grenville–Sveco-Norwegian or Dalslandian, and late Caledonian orogenies, respectively) had little effect. COCORP reflection profiling in the southern Appalachians5 has demonstrated that crystalline ‘basement’ has been thrust for a large distance over autochthonous early Palaeozoic sediments of the proto-Atlantic continental margin. Data from a seismic profile6 across the More Gneiss Region (often called the northwestern basal gneisses of southern Norway) show evidence of P-wave velocity reversal at a depth of about 14 km, and the associated low-velocity layer (LVL) has a thickness of 4 km. As there is no excess of heat flow to account for the LVL, we consider here the hypothesis that oceanic crust and accompanying sediments have been subducted under the gneisses.

Metamorphism of the Seve Nappes at Åreskutan, Swedish Caledonides

Abstract Two Seve Nappes occur in the Åreskutan area. The lower nappe is composed of a layered sequence of tectonized metasediments and amphibolites, metamorphosed in the amphibolite facies. The upper nappe (Åreskutan Nappe) consists of high-grade migmatitic gneisses and metabasites. The two nappes are separated by a mylonite zone. A remnant of extensively mylonitized Särv Nappe is believed to occur between the Lower Seve Nappe and the Silurian rocks of the Lower Allochthon. The Särv Nappe is metamorphosed in greenschist facies. A phyllonitic zone separates the Särv Nappe from the Lower Seve Nappe. The mineral assemblage in the amphibolite facies Lower Seve Nappe indicates recrystallization temperatures around 550°C and pressures of 200–500 MPa. The distribution coefficients for the partitioning of Mg and Fe between biotite and garnet are about K D = 0.18. Strong retrogression occurred in the mylonitic basal parts of the Särv and Seve Nappes during Caledonian nappe translation. In the gneisses of the Åreskutan Nappe, a granulite facies metamorphism at >650°C and > 500–700 MPa was overprinted by amphibolite facies metamorphism. Biotite-garnet K D-vaIues from the Åreskutan Nappe cluster around 0.30, indicative of high-grade metamorphism. Polymetamorphism is possibly reflected by a considerable spreading of the K D-values from 0.26 to 0.58. Caledonian pegmatites cut the Åreskutan Nappe. They are mylonitized at the base of the nappe. No retrogression has taken place during the formation of the mylonitic foliation, which indicates that this process took place under relatively high-grade conditions. This is confirmed by the K D-values from recrystallized garnets and biotites in the mylonite. It is believed, therefore, that this mylonite formed during Caledonian nappe translation, when the Åreskutan Nappe was superposed on the Lower Seve Nappe. Subsequent displacement of the two Seve Nappes together on to the underlying tectonic units occurred under much lower metamorphic conditions. Recent Rb-Sr age determinations suggest that a high-grade metamorphism of the Åreskutan Nappe is of Caledonian age, although the rocks of this nappe may have had a pre-Caledonian history. The few age determinations (fission track) of minerals in the Lower Seve Nappe gave Proterozoic ages.

On the thermal stability of Rb-Sr and K-Ar biotite systems: Evidence from coexisting Sveconorwegian (ca 870 Ma) and Caledonian (ca 400 Ma) biotites in SW Norway

The Caledonian orogeny has imposed a zone of greenschist facies metamorphism on the high-grade Sveconorwegian basement along the front of the Caledonian nappe system in S.W. Norway. In this zone a Caledonian generation of green biotite (ca 400 Ma old) has developed, indicating a metamorphic temperature of about 400° C. This Caledonian biotite occurs side by side with relicts of a Sveconorwegian generation of brown biotite (ca 870 Ma old). The somewhat younger ages obtained from a number of brown biotites can be related to a partial transformation of the old biotite to titanite+green biotite during the Caledonian metamorphic recrystallization. Loss of radiogenic Ar and Sr from the biotite by volume diffusion apparently has not been operative, even at a temperature as high as 400° C. The Sveconorwegian biotite appears to have remained virtually closed to K-Ar and Rb-Sr up to the break-down due to metamorphic recrystallization.

Caledonian deformation in Norway

Geological research and mapping over the last decade has led to a reassessment of the Caledonian orogen in Norway. Two principal stages of orogenesis are now established: (1) a late Cambrian to early Ordovician Finnmarkian or Grampian event recognized mainly in Finnmark and probably also developed in western Norway; and (2) the widespread Middle-Upper Silurian Scandinavian stage of central and southern areas. Another significant finding, aided by radiometric studies, is that of incorporation of Precambrian crystallines as discrete tectonic slices within the Caledonian nappe complexes, reminiscent of the Lewisian-within-Moine relationship of Scotland. In the extensive gneiss terrain of western districts and of Lofoten the effects of Caledonian tectonometamorphic reconstitution have been minimal. Biostratigraphic and geochronological indicators provide evidence that diachroneity is a major feature common to both the above evorogenic stages, with deformation younging progressively towards the southeastern quadrant. In S Norway, folding and local thrusting continued into the Devonian. In terms of geometry and strain, individual nappes are generally extensive, thin, sheet or westward-thinning elements in which protracted high strains in basal zones have produced complex, banded mylonitic and pseudo-psammitic lithologies. Indications of an overall, primary, progressive simple shear deformation are ubiquitous, commonly with evidence of fold rotation into the stretching lineation trend in areas of high ductile strain; this is masked by important episodic increments of flattening and extensional strain producing lensoid, mega-boudin structures and leading to excision of some nappe units. This vertical shortening and gravitational spreading is recognized in both the Cambrian and the Silurian stages of the orogenesis and affects calculations of nappe translation, estimated in hundreds of km for central and southern areas. In conclusion, some comparisons are outlined between the Scandinavian and East Greenland Caledonides; in these two segments of the orogen, nappe displacement is in opposite directions.

Silurian or Upper ordovician fossils at Guolasjav'ri Troms, Norway

In August 1979, specimens of rugose and tabulate corals, crinoids and brachiopods (Fig. 1a) were recovered from meta-limestones in a belt extending 0–3.5 km north-west of Guolasjav'ri, a mountain lake south-east of Kaafjord, Troms, in Norway (Fig. 2, locality I). This is the first fauna to be recognised in this part of the Caledonian nappe sequence in Troms. The presence of corals proves that these metalimestones are not older than Middle Ordovician which imposes constraints on the correlation of this series with units in the Caledonides to the north and south and has an important bearing on the problematic relationship between the dominant Scandian phase (mid-Silurian1) of the Central Scandinavian Caledonides and the Finnmarkian phase (late Cambrian2) of northernmost Scandinavia.

Mineralization controls in the sandstone lead-zinc deposits at Vassbo, Sweden

The sandstone-lead-zinc mineralization in the Vassbo region of west-central Sweden is concentrated in two deposits, Vassbo and Guttusjoe. The ores occur in Lower Cambrian quartz sandstones in a thin sedimentary sequence, underlain by a Precambrian basement and overlain by Caledonian nappes. Although the ores are stratabound, mineralization occurs in suitable arenaceous horizons throughout the sedimentary sequence.The Precambrian basement is crossed by a number of diabases dated at 1,100 to 1,350 m.y. Erosion of these diabases and their associated joints led to the formation of basement depressions. This is reflected in thickening in the overlying sediments. The distribution of mineralization in the area is found to be strongly controlled by the location of the basement diabases and, consequently, the sediment thickness. The recognition of this relationship and the fact that the subsurface location of the diabase dikes could be traced by aeromagnetics led to the discovery of the Guttusjoe deposit.Within the ores, mineralization is strongly controlled by sedimentary structures. However, the ore minerals infill the interstices between the sand grains, and thus high ore concentrations are independent of sedimentary structures. The spatial relationships suggest that the mineralization originated through penetration of the sedimentary sequence by solutions, preferentially flowing along the low pressure conduits provided by the thicker sandstones overlying the diabases.

Studies on the genesis of the Laisvall sandstone lead-zinc deposit, Sweden

The Laisvall deposit in Swedish Lappland is one of a series of sandstone lead-zinc deposits at the border of the Caledonian mountains. The total ore reserves were estimated to be 80 million tons of 4 percent lead and zinc.The ore is located mainly in two thin sandstone horizons in a late Precambrian-Cambrian autochthonous sedimentary sequence overlying a Proterozoic crystalline basement and covered by nappe slices related to the Caledonian orogeny. The sandstones were deposited on a stable platform at the shallow, tidal margin of the proto-Atlantic.Nappe translation into the area was accompanied by minimal disturbance of the Laisvall autochthonous sediments. Disruption of the alum shales, which formed the sole of the lowermost nappe, flexure folding, and some faulting are the major tectonic effects. The ore has suffered folding, faulting, and overthrusting, and thus predates the arrival of the Caledonian nappes into the area. An illite crystallinity study reveals that thermal effects of the overthrusting were limited to within 20 m of the lowermost nappe. This is consistent with textural observations on the sandstones and ore minerals suggesting that the major metamorphic effect on the ore was caused by low-temperature loading. Total recrystallization or remobilization of the deposit is precluded.The minerals of the ore association include galena, sphalerite, calcite, fluorite, and barite. They infill the pore spaces in the sandstones. No definitive paragenesis can be unraveled at Laisvall. The minerals are commonly mutually exclusive and several generations of each mineral exist. However, there is a marked tendency for sphalerite to be generally older than galena, which in turn usually precedes the calcite, barite, and fluorite. The deposit is zoned, particularly with respect to galena and sphalerite, with zinc being dominant in the Upper Sandstone to the northwest and very minor in the galena-rich Lower Sandstones.A fluid inclusion study on the sphalerites shows that the ore was precipitated from a concentrated Na-Ca-Cl brine at around 150 degrees C. No evidence for boiling is found. Sulfur isotopic ratios of the sulfides are not in equilibrium, indicating sequential deposition. The sulfide-sulfur is isotopically heavier than the barite sulfate-sulfur. This indicates that two solutions were involved in the formation of the ore, a sulfidic solution and a low sulfide sulfate solution. Thermodynamic and mass balance considerations suggest that the metals were contained in the sulfate solution.Calcite carbon and oxygen isotope ratios reveal the presence of both sedimentary and hydrothermal carbonate, suggesting partial reaction of hydrothermal solutions with the sedimentary carbonate. Oxygen isotopic ratios are consistent with the fluid inclusion data.The distribution of the ore is mainly controlled by permeability variations in the sandstones caused by the distribution of shale layers and sedimentary structures. Sharp ore contacts in some areas of the deposit indicate that the ore was formed after the deposition of the sandstones. The ore formation temperature, similarities of fluid inclusion properties in sphalerite in probable Caledonide-related joints with bulk ore, and increased crystallinity of illites when in contact with the ore suggest that ore formation was nearer to the arrival of Caledonide nappes in the area.Trace hydrocarbons have been detected in the sphalerite and evidence is presented as to their primary origin, rather than from recent contamination. These observations, together with the fluid inclusion data, suggest that the ore solutions were similar to oil field brines.The accumulated data suggest that pulses of metalliferous, low sulfide brines encountered sulfidic waters in the Laisvall area, leading to precipitation of the ore. Sulfur isotopic evidence indicates that the sulfate was derived from oxidative leaching of sedimentary sulfides and the sulfide possibly from oil-field waters. The metalliferous brines varied in gross chemistry, being zinc-rich initially, lead-rich in the main phase of ore formation, and becoming metal-poor in the later stages. The sulfide solution seems to have been more homogeneous in character.Precipitation occurred at around pH 5 at 150 degrees C from a concentrated chloride solution.Subsequent loading by the nappes effectively sealed the Laisvall sandstone aquifer, leading to the preservation of the ore during the remaining, relatively peaceful, 400 million years of its history.

Caledonian nappe correlation and orogenic history in Scandinavia north of lat 67°N

A comprehensive correlation of the Caledonian nappe pile in northern Scandinavia is attempted for the first rime. The geology of a traverse through the nappes in a part of Troms, Norway, where the structural succession is more complete than elsewhere, forms the main basis for correlations to the northeast and southwest. Seven nappes or nappe complexes (designated 1 through 7, from bottom to top) are distinguished regionally from lat 67°N northward, and probable correlations to central Scandinavian nappes are mentioned. Stratigraphic and structural correlation criteria are emphasized. The nappe pile is shown to contain rock bodies of Ordovician-Silurian age interleaved with older ones that have at least partly undergone pre-Silurian Caledonian deformation and metamorphism; Precambrian units, some of which appear to be at least partially unaffected by Caledonian deformation and metamorphism, are also involved. The interleaving is mainly attributed to nappe tectonics. Most nappes were translated at least 200 to 400 km toward the east or southeast. Most independent movement of nappes 4 through 7 took place synmetamorphically during and shortly after the Middle to Late Silurian metamorphic peak. Major translation of nappe 3 occurred as a lateorogenic event. Nappes 1 and 2 were apparently emplaced before nappe 3, after Ordovician time.

Caledonian Nappe Sequence of Finnmark, Northern Norway, and the Timing of Orogenic Deformation and Metamorphism

On the basis of regional, structural, and metamorphic studies combined with age determinations, it is demonstrated that the internal metamorphic fabrics of the main nappe sequence of Finnmark, northern Norway, developed during an Early Ordovician phase of the Caledonian orogeny (Grampian?); the cleavage development in the autochthon also belongs to this phase. The final mise-en-place of the thrust-nappe sequence, however, appears to belong to a later phase of Caledonian orogenic development, probably toward the end of the Silurian Period, as does the deformation and metamorphism of the Silurian sequence of Mageroy. The geochronological results also give information regarding the positioning of the lower boundaries to the Cambrian and Ordovician Systems.