Straumsvola complex, Queen Maud Land, Eastern Antarctica, Antarctica
|Latitude & Longitude (WGS84):||72° 6' 60'' South , 0° 19' 60'' West|
|Latitude & Longitude (decimal):||-72.11666,-0.33333|
|Köppen climate type:||EF : Ice cap climate|
Straumsvola is a nepheline syenite intrusive complex about 7 km in diameter, which intrudes gneisses of the Jutulrøra Formation (Svedrupfjella Group), located on the eastern edge of the Jutulstraumen Glacier (Ravich & Solov'yev, 1966 and 1969; Hjelle, 1972; Allen et al., 1986; Harris & Grantham, 1993). The Straumsvola nepheline syenite complex consists of a massive outer zone and a layered inner zone, whereas the adjacent nunatak 5 km to the southeast, Tvora, consists of quartz syenite (see http://www.mindat.org/loc-266652.html). The Straumsvola complex is exposed mostly on the nunatak Straumsvola itself, but it can be observed also at the easternmost Storjoen and Joungane nunataks.
The outer zone contains numerous pegmatite dykes (southeast ridge of Straumsvola and summit ridge of Storjoen) consisting of alkali feldspar, biotite, sodium-rich pyroxene and amphibole. Such pegmatite dykes can contain cavities up to several metres in diametre, in which large, well-formed crystals of feldspar, amphibole, aegirine, zircon (up to 2 cm accross), analcime, and natrolite are present. Natrolite prismatic crystals are partially enclosed by icositetrahedra of analcime.
The layered rocks are exclusively exposed on Straumsvola. Near the summit of Straumsvola a more mafic facies unconformably overlies the layered zone.
A large number of Jurassic dykes cut the two plutons and the surrounding country-rocks. These dykes are extremely varied in composition and include nephelinites, pyroxenites, lamprophyres, dolerites, phonolites, and peralkaline microgranites. Jurassic dykes of western Dronning Maud Land dyke swarms are probably related to magmatism associated with the Karoo large igneous province in Africa.
In one unusual dyke of peralkaline granite, which crops out on the north ridge of Straumsvola at about 200 m from the summit and cuts both the nepheline syenite country-rock and several dolerite dykes, REE-rich eudialyte occurs together with the rare mineral dalyite (Harris & Rickard, 1987). In other dykes of peralkaline granite narsarsukite and vlasovite have been found (Harris & Grantham, 1993).
Eudialyte is found in fissures and vugs throughout the upper layered zone syenites and in one case as a major phase (up to 20 modal %) in a pegmatite dyke located 100 m south of Straumsvola summit (Harris & Grantham, 1993).
25 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
Age: Anthropocene ( Ma)
Comments: Antarctic Ice Cap
Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529.