South Greenland Research Articles

Erosion and Vegetational Changes in South Greenland Caused by Agriculture

Fredskild, Bent: Erosion and Vegetational Changes in South Greenland, Caused by Agriculture. Geografisk Tidsskrift 92:14–21. Copenhagen 1992. Pollen analyses and measurements of magnetic parameters in some lakes and ponds in sub-arctic South Greenland have shown, that after stable conditions through most of the Holocene drastic environmental, changes appeared as a result of the introduction of agriculture by the Norsemen c. A.D. 1000: the vegetation cover was broken by wood cutting and grazing, and soil erosion began. After c. five centuries the Norsemen died out, the vegetation began recovering and soil erosion decreased. After some centuries of stabilizing environmental conditions, the reintroduction of sheep breeding in the beginning of the 20th century has caused a new period of vegetational changes and increasing soil erosion.

The palaeomagnetism of major (middle proterozoic) igneous complexes, South Greenland and the Gardar apparent polar wander track

The Gardar Province comprises a major rift-related igneous suite emplaced in three pulses at ca. 1300–1280 Ma, ca. 1220 Ma and 1160–1125 Ma. This study reports a palaeomagnetic study of the northeastern sector of the present outcrop and incorporates igneous units belonging to the first and last episodes. Early lavas from the basal part of the rift infill record a reversal of magnetisation and define a palaeomagnetic pole at 207°E, 10°N ( 5 sites, dp/dm= 7 14° ). This primary magnetisation record has been partially overprinted in the aureoles of large alkaline complexes. The latter plutons include the North Qoroq intrusion (1291 ± 61 Ma) yielding a pole position at 203°E, 13°N ( 65 samples from 12 sites, dp/dm= 6 12° ), the Motzfeldt intrusion (1291 ± 31 Ma) yielding a pole position at 212°E, 10°N ( 25 samples, dp/dm= 6 12° ), and the Narssarssuaq Stock yielding a pole position at 207°E, 9°N ( 23 samples, dp/dm= 4 7° ). The younger South Qoroq complex (1160 ± 8 Ma) yields a pole position at 216°E, 42°N ( 67 samples from 9 sites, dp/dm= 11 16° ). Positive contact tests indicate primary cooling-related magnetisations. These bodies are predominantly of single polarity equivalent to W + directions of magnetisations although reversals are recorded. The majority of a suite of NE-SW trending dykes emplaced at ca. 1154–1143 Ma are magnetised in a similar direction [ D/I= sol3 51° , pole position at 231°E, 33°N ( 18 dykes, dp/dm= 5 7° )] to the slightly-older South Qoroq complex. Together with earlier results from the Gardar Province, these data define a motion of the region from shallow to equatorial and then back to intermediate palaeolatitudes between 1290 and 1140 Ma. Pole positions trace out an apparent polar wander path comprising a small loop followed by a long track. This track is the outward path of the “Great Logan” palaeomagnetic loop for which data from the Keweenawan Province of North America (ca. 1100–1050 Ma) define the return path. The loop was executed between ca. 1200 and 1050 Ma following a near-static interval between ca. 1290 and 1200 Ma. This long static interval was also characterised by constant field polarity. Asymmetry of geomagnetic field reversals is recognised in early Gardar events; it is not apparent in younger Gardar data although it recurs in Keweenawan times.

A revised magnetostratigraphy for the Mid-Proterozoic Gardar lava succession, South Greenland

New palaeomagnetic results from the ca. 1300 Ma Gardar lava succession within the Eriksfjord Formation of South Greenland are presented. This study incorporates stepwise thermal demagnetisation of 256 samples from 66 lava flows from all three lava groups in this formation, accompanied by principal component analysis. The results identify two complete reversals (N → R → N) in the upper lava group and two (R → N and N → R) in the lower group, with a possible palaeoexcursion in the lower group. A minimum of two further reversals are predicted in the time interval represented by the sandstone units intercalated with the lava flows. Both complete reversals in the upper group exhibit inclination asymmetries of 30°. This degree of asymmetry is satisfied by a geomagnetic field model equivalent to a dipole axially offset by 570 km. However, a more complex source is not precluded by the present evidence. Four new pole positions are calculated for the Gardar lavas, two for the upper lava group and one each for the middle and lower groups. The middle lava group shows an anomalous mean direction and pole position, which is unrepresentative of the remainder of the lava succession and is thought to record a virtual geomagnetic pole representative of a transitional field direction. The presence of a non-axial geocentric dipole field means that the use of the Laurentian apparent polar wander path for dating the new poles is not valid.

Feldspar megacrysts and anorthosite xenolith-bearing dykes in the Narssarssuaq area, South Greenland

Numerous dyke intrusions are found in the Narssarssuaq area of the Gardar province, a Mid-Proterozoic intracontinental rift system. Ten to fifteen percent of these dykes, which range in composition from trachybasalt to phonolite and rhyolite, contain significant proportions of feldspar megacrysts and occasionally anorthosite xenoliths. Two groups of dykes are distinguished; the older group is more alkaline, richer in incompatible elements and contains more anorthosite xenoliths than the younger. It is probable that the main reason for the differences is variation in magma production through time and from one area to another. Chemical zonation in the dykes reflects compositional gradients in the feeding magma reservoirs; the magma reservoirs acting as open systems in which crystal fractionation was an important controlling process. The anorthosite xenoliths are not strictly cognate with their hosts, but were derived from comparable alkaline magmas with a composition roughly corresponding to the most primitive of the dykes. The plagioclase megacrysts were presumably formed at an early stage of the development of the magma chambers. Rb-Sr dating of one of the dykes from the older group of dykes gives an age of 1206 ± 20 Ma and an initial 87Sr/86Sr ratio of 0.7028 ± 0.0001 supporting a low degree of contamination with upper crustal Sr.

Cathodoluminescence Petrography of Middle Proterozoic extrusive carbonatite from Qasiarsuk, South Greenland

AbstractThe amygdaloidal carbonatite lavas at Qasiarsuk have a primary phenocryst assemblage of calcite, fluor-apatite and magnetite set in a groundmass of calcite, apatite and iron oxides, and minor dolomite. Cathodoluminescence reveals a complex history, both for the major minerals which show zonal growth, and for important Nb andREEaccessory phases which include pyrochlore and perovskite. TheREEreside in fluor/hydrous-carbonates included exclusively in apatite. TheseREEminerals are similar to synthetic phases from hydrothermal experiments, but probably crystallised in equilibrium with a late-stage volatile-rich carbonate melt. Apart from low-temperature alteration, the rocks have been little disturbed since their extrusion during the earliest phase of development of the Gardar Alkaline Igneous Province.

Biotite Equilibria and Fluid Circulation in the Klokken Intrusion

Chemical variation in biotite from the KJokken gabbro-syenite intrusion in the Proterozoic Gardar province in South Greenland has been investigated by electron probe and, for F and Li, ion microprobe. Most mica occurs in small amounts as fringes on ilmenomagnetite or fayalite, rarely as an intercumulus or poikilitic phase. The micas range continuously from Phlog70Ann30 in a gabbro, to Phlog4Ann96 in the most evolved (slightly persilicic and peralkaline) syenite. In the syenites Fe-Mg partitioning between biotite and olivine can be described by a single distribution coefficient, K6 = Xfi X%? /X^-Xf°'~3, suggesting that these reactant phases mix ideally at the reaction T. Experimental data for Fe-Mg exchange via aqueous chloride solutions (Schulien, 1980) imply low T (~ 320 °Q. F was absent in the experiments and may significantly affect the exchange equilibrium. K6 in the gabbros is ~ 1, consistent with equilibrium via a fluid depleted in F because of crystallization of large amounts of amphibole. Al, Mn, and Ti vary regularly throughout the series and can be used as markers of cryptic variation in the layered syenites. (Al + Si): 22 O is always in the range 7-7—7-85. A1/(A1 + Si) decreases from ~O31 in gabbros to 0-25 in the most Fe-rich micas. Li is always 300 °C subsolidus even when texturally intercumulus. Stable isotope data are consistent with the separation and retention of a deuteric fluid during the final stage of magmatic crystallization. Klokken was not generally subject to the pervasive, long-range (in both distance and time) dydrothermal interactions demonstrated in

Cathodoluminescence and microporosity in alkali feldspars from the Blå Måne Sø perthosite, South Greenland

AbstractSamples from a traverse across the Blå Måne Sø perthosite unit in the Tugtutôq Central Complex of the Gardar province, South Greenland have been examined for cathodoluminescence characteristics, microporosity and δ18O isotopic values. Reddening of cathodoluminescence colours in alkali feldspars (normally blue) from the unit may be correlated with increased microporosity of the feldspars as determined using scanning electron microscopy. δ18O values of all samples lie within the range of values expected of juvenile fluids, independent of the level of alteration indicated by cathodoluminescence studies.Observations are consistent with previous suggestions that levels of alkali feldspar microporosity and levels of fluid alteration (as determined by cathodoluminescence of alkali feldspars) are related phenomena. Oxygen isotope ratios suggest that the fluid is largely juvenile in origin, with, perhaps, some meteoric (low δ18O) component.

Compositional zoning in hydrothermal aegirine from fenites in the Proterozoic Gardar Province, South Greenland

Compositionally aoned Ti-bearing aegirine is a common constituent in fenites and hydrothermal veins and vugs associated with nepheline syenites from the mid-Proterozoic Gardar Province of South Greenland. A typical assemblage in these mineralization includes quartz, albite, microcline, aegirine, calcite, stilpnomelane, apatite, monazite and Nb-Fe-Ti-Mn oxides, with a wide range of unusual REE-Zn-Be-Ba-Mn-silicates as accessory phases. Individual aegirine crystals display evidence of sequential growth, concentric- and sector-zoning that represent large variations in wt. % TiO 2 (0.1-3.0), Na 2 O (11.6-12.8), CaO (0.0-2.0), FeO t (25.4-30.9) and ZrO 2 (0.0-0.74). Concentrations of Al 2 O 3 (<1.34 but typically less than 0.7 wt. %) and MgO (<0.76 but typically less than 0.4 wt. %) are both very low. In terms of pyroxene end-members, these compositions correspond to from 70-95 mole % NaFe 3+ [Si 2 O 6 ] (Aegirine), <1-6 mole % NaAl[Si 2 O 6 ] (Jadeite), <1-8 mole % Ca (Mg,Fe 2+ )[Sii2O 6 ] (Enstatite-Ferrosillite), and from <mole % of an unnamed end-member having the composition Na(Mg,Fe 2+ ) 0.5 (Ti,Zr) 0.5 [Si 2 O 6 ]. As such, the principal chemical variation in the analyzed crystals involves the substitution : VI (Fe 2+ ,Mg)+ VI (Ti 4+ =2 VI (Fe 3+ ) in the M1-position. Textural relationships, together with the chemical inhomogeneities of the pyroxenes, suggest rapid nonequilibrium crystallization from a hydrothermal fluid of changing composition and/or temperature

Conversion of nepheline to sodalite during subsolidus processes in alkaline rocks

AbstractCathodoluminescence (CL) petrography of nepheline syenites of the Igaliko complex, Gardar province, South Greenland shows that sodalites possess embayed contacts against nepheline, and have formed by a process of metasomatic replacement. This texture is demonstrated clearly by CL, since sodalite luminesces bright orange and nepheline is poorly luminescent. The transformation from nepheline to sodalite results in a volume change which leads to a network of fractures in which deep-blue luminescent fluorite is precipitated. Fluorite is formed since the chlorination process involved in the transformation causes localised reductions of the salinity of the fluid and therefore a decrease in the solubility of fluorite. Sodalite-fluorite textures observed using CL allow sodalites of secondary origin in alkaline igneous rocks to be identified.Nephelines and sodalites, when observed using scanning electron microscopy, possess small micropores. By analogy with recent work on alkali feldspars, pervasive alteration of nephelines may occur by fluid flow assisted by a permeable micropore network.

High-technology metals in alkaline and carbonatitic rocks in Greenland: recognition and exploration

High-technology metals such as Zr, Y, Nb, Ta, ree and Ga are generally associated with alkaline and carbonatitic rocks. The recognition of alkaline magmatic provinces or carbonatitic complexes is, therefore, a first step in the exploration for high-technology metals. Low-density exploration data over large parts of South and West Greenland including airborne gamma-ray spectrometry and stream sediment surveys clearly delineate the extension of a major Proterozoic alkaline igneous province and two Phanerozoic carbonatite complexes. On a reconnaissance scale, Nb in stream sediment is the best indicator and gave distinct anomaly patterns over all of the alkaline and carbonatitic intrusive complexes. The anomaly patterns for Y, Zr, Ga, Mn, Sr, Zn, U, and Th also reflect the alkaline/carbonatite intrusions but they are less regular and consistent. In the alkaline Gardar igneous province in South Greenland, two prospects in the Ilimaussaq intrusion relate to rock units rich in eudialyte (Zr, Y, ree). Some of the eudialyte-rich zones were located by geological mapping and visual recognition of this red mineral; elsewhere in the fine-grained eudialyte-bearing rocks, analyses of chip samples and drilling were used. In the Motzfeldt intrusion of the Gardar province, zones of intense hydrothermal alteration are enriched in Nb, Ta, Zr, ree, U and Th. The mineralised zones were located by helicopter-borne gamma spectrometry and subsequently grid sampled to assess Nb and Ta contents. In the Sarfartôq carbonatite complex, alteration zones with massive pyrochlore (Nb) were located by airborne and ground radiometry combined with detailed stream sediment sampling. In the Qaqarssuk carbonatite, minor pyrochlore concentrations and ree-bearing veins have been discovered during exploration for apatite. Based on this experience it is concluded that alkaline and carbonatite complexes are easily recognised in low-density geochemical data. Ore zones have been located using radiometric methods combined with geological mapping and detailed geochemical surveying.

Early Proterozoic collision tectonics, and rapakivi granites as intrusions in an extensional thrust-thickened crust: The Ketilidian orogen, South Greenland

The Ketilidian orogen, that extends east-west across southern Greenland, formed in the period 1740–1850 Ma. In a north to south profile there are the following interpreted tectonic zones: a shelf-foredeep which has been thrust northwards to the foreland and back-folded and thrust southwards towards the suture, and which overlies Archean basement with Ketilidian granites with an appreciable crustal melt component; a suture with basaltic lavas, gabbros, shear belts, mylonites, copper and gold mineralisation; an Andean-type granitic batholith intruded into an island arc of volcanics, gneissose plutons and layered noritic gabbros; a steep back-arc shear belt of high-strain gneisses; and a flat-lying thrust stack of meta-supracrustals and paragneisses intruded by, largely crustal-melt, rapakivi granites. It is proposed that this profile is analagous to that from the Himalayas to Tibet, and that the rapakivi granites are equivalent to the Baltoro batholith in the Karakoram at the western uplifted end of the Tibetan plateau. Crustal thickening was achieved by thrusting, and ensuing thermal relaxation led to partial dehydration melting of deep continental crust. This provides a new model for the tectonic environment of rapakivi granites as intrusions in extensional zones within a collapsing thrust-thickened crust.

Textural evolution of the rapakivi granites, south Greenland ?Sr, O and H isotopic investigations

The development of rapakivi texture in feldspars from the Ketilidian granitoids of south Greenland has been investigated using Sr, O and H isotopes. A low temperature signature is found in the Sr and O data which seemingly contradicts some textural features that point to a magmatic origin of the plagioclase mantles around the K-feldspar ovoids. An origin for these mantles involving exsolution from an original alkali feldspar solid solution is proposed, which involves growth of mantles over a range of conditions determined by the mobility of the exsolving sodic feldspar. This mobility may be enhanced at high temperatures in the presence of melts or increased fluid pressures and at lower temperatures by the processes responsible for the transformation of K-feldspar to microcline. Rapakivi granites with both white and dark green feldspar occur in south Greenland but show no major isotopic differences, although the dark alkali feldspars contain significantly more fluid. Equivalent fluids in the white alkali feldspars may have escaped during plagioclase exsolution.

Ornamental stones in West and South Greenland

In the spring of 1990 the Greenland Home Rule administration initiated a project to evaluate the potential for ornamental stones in West and South Greenland, with support from the Geological Survey of Greenland (GGU). The project was established in view of an interesting new development of the international ornamental stone market which might be exploited to diversify the economy and provide new job opportunities in Greenland.

Geochemical mapping: distribution of gold, arsenic, antimony and tantalum in South Greenland

New graphics software utilising raster techniques has been developed at the Geological Survey of Greenland (GGU) during 1989 and 1990 for presentation of geochemical and geophysical areal data. The software is very suitable for the display of the regional variation of chemical elements as contoured colour maps of interpolated data. In this paper we show the distribution patterns for a few selected elements of economic interest, which have been determined in stream sediment samples collected in South Greenland in 1979. The implications of the new information for the mineral potential of the region are briefly discussed.

Seasonal variations in the concentration of 10Be, Cl −, NO 3−, SO 42−, H 2O 2, 210Pb, 3H, mineral dust, and σ 18O in greenland snow

A detailed snow pit study at Dye 3, South Greenland, has been carried out in order to investigate the seasonal variations of 10Be, Cl −, NO 3 −, SO 4 2−, H 2O 2, 210Pb, 3H, Mn and σ 18O. Special emphasis was placed on understanding the causes of 10Be variations because this isotope can be used to trace the history of solar activity. A sampling interval of 5 cm was chosen to assure a mean time resolution of about 20 samples per year for the period 1978–1983. Four different categories of seasonal variations were identified: strong summer peaks (σ 18O, H 2O 2, 3H), weak bimodal peaks (NO 3 −, SO 4 2−, conductivity, 10Be), a fall peak ( 210Pb) and a winter-spring peak (Cl −, Mn). Although we are still far from a detailed understanding of the mechanisms which control the measured compositions, there are indications that different processes dominate at different seasons. NO 3 −, SO 4 2−, Mn and Cl − variations suggest that aerosol transport is most important during winter-spring. In summer-fall there seems to exist a second period of long range transport from low latitude continental areas resulting in enhanced concentrations of 210Pb, 10Be and SO 4 2−.

Paleothermometry by control methods

AbstractThe recovery of past climatic conditions from ice-sheet borehole temperatures can best be accomplished using the calculus of variations (control methods) to minimize mismatch between the observed profile and a solution of the heat equation which depends on the unknown climate history. Here, we use control methods and a simple one-dimensional heat equation and the temperature depth profile observed at Dye-3 to infer the surface temperature of south Greenland over the last 30 000 years. This history illustrates the virtues that recommend control methods for future use in borehole-temperature analysis, namely: (i) it meets objective performance criteria, and (ii) its uncertainty can be established quantitatively. Our inferred climate history displays what may be the Younger Dryas cold event at about 9000 years BP. Borehole paleothermometry by control methods may thus resolve the controversy concerning the interpretation of Greenland ice-core isotope records.

Paleothermometry by control methods

AbstractThe recovery of past climatic conditions from ice-sheet borehole temperatures can best be accomplished using the calculus of variations (control methods) to minimize mismatch between the observed profile and a solution of the heat equation which depends on the unknown climate history. Here, we use control methods and a simple one-dimensional heat equation and the temperature depth profile observed at Dye-3 to infer the surface temperature of south Greenland over the last 30 000 years. This history illustrates the virtues that recommend control methods for future use in borehole-temperature analysis, namely: (i) it meets objective performance criteria, and (ii) its uncertainty can be established quantitatively. Our inferred climate history displays what may be the Younger Dryas cold event at about 9000 years BP. Borehole paleothermometry by control methods may thus resolve the controversy concerning the interpretation of Greenland ice-core isotope records.

Zirconium and niobium-bearing ilmenites from the Igaliko dyke swarm, South Greenland

AbstractIlmenites from alkaline basic dykes in the Gardar province, south Greenland have Zr contents up to 3850ppm and Nb contents up to 1030ppm. These elements substitute for Ti in the octahedral site. These are amongst the highest recorded Zr and Nb contents for ilmenites, giving distribution coefficients (Kdilmenite/matrix) for Zr up to 11.6 and Nb up to 70.3. Fractionation of ilmenite may thus have a dramatic effect on residual Zr and Nb contents. These effects are discussed in relation to the use of trace element tectonomagmatic discrimination diagrams.

Ion microprobe study of intragrain micropermeability in alkali feldspars

Alkali feldspar cleavage fragments from the Klokken layered syenite, South Greenland, were heated to 700°C at 0.1 GPa in 99% H218O for 75 h. These samples were then polished and imaged by ion microprobe for 18O. The feldspars were known to contain areas of pristine, braid micro-perthite which were not turbid and areas of deuteric patch perthite which were turbid. Turbidity is related to the presence of micropores in the feldspars. On imaging the grain, it was found that the 18O had penetrated into the parts of the grain which were microporous and not into the pristine areas. Micropores are therefore responsible for rendering the feldspars permeable as well as porous. The implications of micropermeable feldspars in several areas of geology are discussed.

Geochemical patterns related to major tectono-stratigraphic units in the Precambrian of northern Scandinavia and Greenland

Abstract Large areas of the Fennoscandian Shield (Norway, Sweden, Finland) and the Laurentian Shield (Greenland, Canada) have been covered by regional geochemical surveys based on low-density sampling of various surficial materials. Till and sediment, organic matter and moss from streams were collected at an average density of 1 site per 30 km 2 over 250,000 km 2 of northern Fennoscandia. The geochemical patterns reflect both the major Precambrian tectono-stratigraphic units, and also distinguish sub-units, e.g., Archaean gneiss units, ultramafic predominance within greenstone belts, and granites enriched in incompatible elements. In Greenland, stream sediment was collected over 35,000 km 2 of Archaean and Proterozoic rocks at a density of 1 site per 20–30 km 2 in the west, and at 1 site per 2–5 km 2 in the south. Stream sediment data display geochemical boundaries that coincide with recently defined tectono-stratigraphic units in Archaean gneisses. The Proterozoic of South Greenland is enriched in U and other incompatible elements, resembling the Fennoscandian Shield. A major Nb province outlines alkaline magmatism associated with Late Proterozoic rifting. Widely scattered isotopic data and plate-tectonic models have been used to correlate the evolution of the Fennoscandian and Laurentian shields. The regional geochemical data distinguish major boundaries and provinces, will aid in further correlation, and help to unravel crustal evolution.