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M. Knoper¹ ², C. Jackson¹, P. Harris², G. Ferrar¹, J. Krynauw¹, A. Moyes², & C. Harris³
¹Department of Geology and Applied Geology,
University of Natal, Private Bag X10, Dalbridge 4014,
South Africa
²Hugh Allsopp Laboratory, BPI Building,
University of the Witswatersrand, Private Bag 3,
Wits 2050, South Africa
³Department of Geological Sciences,
University of Cape Town, Rondebosch 7700, South Africa
Present address of first author:
Dept. of Geology, Rand Afrikaans University,
P.O. Box 524, Auckland Park 2006, South Africa
The Kirwanveggen is a 180 km long discontinuous, steep-sided ridge of ice falls and nunataks situated in western Dronning Maud Land. This SW-NE oriented chain of nunataks was the focus of field work by members of the South African National Antarctic Programme during 1991-1995. Field work accomplished during this period refined previous research in the Kirwanveggen (summarized by Wolmarans and Kent, 1982) and subdivided the Kirwanveggen into three areas, namely, the northern, central, and southern Kirwanveggen. This subdivision is based on contrasting rock types, structural geometries and styles, metamorphic grades and retrograde alteration. (Detailed geological maps of the Kirwanveggen are available in digital format from the first five authors.)
The northern (Fig. 1) and central (Fig. 2) Kirwanveggen are dominated by polydeformed gneisses of the Meso-Neoproterozoic Sverdrupfjella Group; except for the Jurassic Sistefjell syenite complex (173±2 Ma, MSWD=0.123, Rb-Sr whole rock) which intrudes volcanic rocks of unknown age in the isolated easternmost nunataks of the northern Kirwanveggen. (Harris, 1995). The contact of the Sistefjell syenite with the Sverdrupfjella Group is not exposed. The Sverdrupfjella Group consists of four broadly defined categories of gneisses: megacrystic augen gneisses, leucogneisses, granitic gneisses, and a variety of migmatitic mafic-intermediate to quartzofeldspathic banded gneisses. The origin of these gneisses is associated with 1200-1000 Ma orogenesis but the gneisses have been reworked during later tectonothermal events (Grantham et al, 1995) as constrained by multiple generations of deformed mafic and leucocratic dykes (Jackson, 1995). The augen gneisses and leucogneisses of the Sverdrupjella Group are interpreted as meta-intrusive rocks, whereas many of the banded migmatitic and quartz-feldspar gneisses most likely represent a composite of tectonized intrusive and supracrustal protoliths. Zircon ion microprobe results on banded migmatitic gneiss from the northern Kirwanveggen indicate ages of 1157±10 Ma, leucosomes yield zircon ion microprobe ages of 1098±5 Ma (Harris et al, 1995a, 1995b). A common unit is the Kirwanveggen megacrystic orthogneiss which yields zircon ion microprobe ages of 1088±10 Ma at Neumayerskarvet (Harris et al, 1995a).
The southern (Fig. 3) Kirwanveggen is characterized by a diverse collection of rock types. From Lagfjella to Tunga, the Kirwanveggen Basalt Formation (Harris et al, 1990) with a 40Ar/39Ar age of 180±2 Ma (determined by R. Duncan, in collaboration with C. Harris) unconformably overlies the Amelang Plateau Formation. The latter Formation in turn unconformably overlies the Urfjell Group at Tunga, and the Sverdrupfjella Group at Ladfjella and Lagfjella. Plant remains in the lower stratum of the Amelang Plateau Formation show affinity to an Early Permian flora (Larsson, 1995). The Urfjell Group is dominated by massive current-bedded quartzites and poorly sorted conglomerates suggestive of a high energy depositional environment. The Urfjell Group has a distinctive fracture cleavage; strata have subvertical dips below the Amelang Plateau Formation at Tunga and are in fault contact with schists and gneisses at Uven. An apparent Rb-Sr whole rock age of 539±29 (MSWD=31) may indicate a diagenetic age (Moyes et al, 1995). Precise contact relationships of both the Urjell and Sverdrupfjella Groups with low-grade schists, phyllites, and granites in the southernmost part of the Urfjell nunataks are unknown due to limited outcrop exposure. Undifferentiated gneisses of the Sverdrupfjella Group are best exposed in the Lagfjella and Ladfjella, and are considered to be correlatives of gneisses in the northern and central Kirwanveggen.
Aucamp, A.P.H., Wolmarans, L.G., and Neethling, D.C., 1972, The Urfjell Group, a deformed (?) Early Palaeozoic sedimentary sequence, Kirwanveggen, western Dronning Maud Land, Adie, R.J., (editor), Antarctic Geology and Geophysics, Universitetsforlaget, Oslo, International Union of Geological Sciences, series B, no. 1, p. 557-562.
Grantham, G.H., Jackson, C., Moyes, A.B., Groenewald, P.B., Harris, P.D., Ferrar, G., and Krynauw, J.R., 1995, The tectonothermal evolution of the Kirwanveggen - H.U. Sverdrupfjella areas, Dronning Maud Land, Antarctica, Precambrian Research, vol. 75, p. 209-229.
Harris, C., 1995, Petrogenesis of the Sistefjell syenite complex, Dronning Maud Land, Antarctica: generation of low delta18O magmas by crustal contamination of rift zone magmas, Geological Society of South Africa Centennial Geocongress, Extended Abstracts, vol. 1, p. 235-238.
Harris, C., Marsh, J.S., Duncan, A.R., and Erlank, A.J., 1990, The petrogenesis of the Kirwan basalts of Dronning Maud Land, Antarctica, Journal of Petrology, vol. 31, p. 341-369.
Harris, P.D., Moyes, A.B., Fanning, C.M., and Armstrong, R.A., 1995a, Zircon ion microprobe results from the Maudheim high-grade gneiss terrane, western Dronning Maud Land, Antarctica, Geological Society of South Africa Centennial Geocongress, Extended Abstracts, vol. 1, p. 240-243.
Harris, P.D., Moyes, A.B., Fanning, C.M., and Armstrong, R.A., 1995b, Zircon ion microprobe constraints on deformation of high grade gneisses in the northern Kirwanveggen, western Dronning Maud Land, Antarctica, VII International Symposium on Antarctic Earth Sciences, Abstracts, p. 183.
Jackson, C., 1995, Colinear deformation within the Meso-Neoproterozoic Kirwanveggen terrain of western Dronning Maud Land, East Antarctica - implications for tectonic models, Geological Society of South Africa Centennial Geocongress, Extended Abstracts, vol. 1, p. 244-246.
Larsson, K., 1995, Permian vertebrate remains from Kirwanveggen, Dronning Maud Land, VII International Symposium on Antarctic Earth Sciences, Abstracts, p. 236.
Moyes, A.B., Knoper, M.W., and Harris, P.D., 1995, The age and significance of the Urfjell Group, western Dronning Maud Land, East Antarctica, VII International Symposium on Antarctic Earth Sciences, Abstracts, p. 277.
Wolmarans, L.G., and Kent, L.E., 1982, Geological investigations in western Dronning Maud Land, Antarctica - a synthesis, South African Journal of Antarctic Research, Supplement 2, 93 p., 3 geological maps.
Field work was accomplished with the assistance of P. Courtnage, M. del Mistro, D. Gold, P. Gräser, W. Johnstone, R. Lewis, M. Mander, I. Manson, and R. Uken. Precise geochronology was determined by collaboration with C.M. Fanning, R. Armstrong, T. Spell, and R. Duncan. Air support was provided by Squadron 30 of the S.A.A.F. Logistical support and funding were provided by the Antarctic and Islands Directorate, Department of Environmental Affairs and Tourism (DEA&T).
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W. Dronning Maud Land
·Web publication date: July 27, 1996·
"Rockscapes" 1996-2001 M Knoper
