Kirwan Volcanics, Queen Maud Land

Faure and T.M. Mensing, The Transantarctic Mountains Rocks, Ice, Meteorites and Water, DOI 10.1007/978-90-481-9390-5 14, Springer Science+Business Media B.V. 2010 

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Magma mixing also causes the isotope composition of strontium of the resulting mixtures to be correlated with the concentrations of other components such as SiO, MgO, and others depending on the chemical composition of the contaminant. Such correlations of isotopic and chemical parameters were first reported by Faure et al. (1972, 1974, 1982) for flows of the Kirkpatrick Basalt in the Transantarctic Mountains and of the Kirwan Volcanic s in Queen Maud Land (Chapter 14). 

Fig. 14.1 Queen (or Dronning) Maud Land is located in East Antarctica along the east coast of the Weddell Sea. It is not considered to be an extension of the Transantarctic Mountains, although it does include flat-lying sandstones of the Permian Amelang Formation which are overlain by continental flood basalts of the Jurassic Kirwan Volcanics. The chemical and isotopic compositions of the basalt flows and sills resemble the Karoo Basalt of southern Africa which was adjacent to Queen Maud Land before the break-up of Gondwana (Adapted from Fumes et al. (1987))...

Fig. 14.3 The Kirwan Escarpment of Queen Maud Land in East Antarctica ( 7 in Fig. 14.2) consists of a large number of nunataks. Some of the nunataks which are composed of the Jurassic lava flows of he Kirwan Volcanics are identified by letters A to J. Faure et al. (1979) analyzed 12 samples of basalt...

The Karoo Basalt, like the Kirwan Volcanics, formed from mantle-derived magma that differentiated by fractional crystallization and concurrent contamination in an open system in contact with granitic gneisses of Precambrian age. The proximity of Queen Maud Land to southern Africa in pre-Jurassic time supports the hypothesis that the Kirwan Volcanics are more closely related to the Karoo Basalt than to the basalt and dolerite of the Ferrar Group (Neethling 1972b Harris et al. 1991 Faure 2001, Fig. 5.67). 

The whole-rock K-Ar dates of basalt dikes and lava flows in the nunataks of Vestfjella in Fig. 14.13 vary widely from 90 to 695 Ma (Appendix 14.5.1). Dates based on plagioclase and groundmass reported by Peters et al. (1991) also scatter. Nevertheless, more than half of the dates are between 160 and 180 Ma, which defines the Middle Jurassic Epoch. These dates support the general conclusion that the Kirwan Volcanics of Queen Maud Land were erupted at about the same time as the Kirkpatrick Basalt and the Ferrar Dolerite in the Transantarctic Mountains and Tasmania (Chapters 12 and 13). The basalt dikes dated by Rex (1967), Fumes and Mitchell (1978), and Peters et al. (1991) yielded slightly younger K-Ar dates than the XdiNdiflows ... 

The numerous basalt dikes which intruded the flows of southern Vestfjella are unaltered in contrast to the flows (Fumes and Mitchell 1978). Nevertheless, Fumes et al. (1982) reported that the initial Sr/ Sr ratios of ten dikes range from 0.70347 to 0.70687 and average 0.70460 0.00061 (2a). This result reinforces the evidence that the initial Sr/ Sr ratios of basalt flows and dikes of the Kirwan Volcanics in Queen Maud Land are not constant and that average values of this ratio are lower than the initial Sr/ Sr ratios of the basalt flows and dolerite sills of the Ferrar Group in the Transantarctic Mountains. 

Several clusters of nunataks in western Queen Maud Land are composed of basalt flows and dikes which are collectively known as the Kirwan Volcanics. These... 

The break-up of Gondwana was initiated by the arrival of a mantle plume in the area between Queen Maud Land of East Antarctica and southern Africa. The stresses imposed on the lithosphere by this plume resulted in the development of a triple junction consisting of crustal rifts. The decompression melting of the rocks in the plume head and in the adjacent lithospheric mantle formed basalt magma which was erupted at the surface to form the Kirwan Volcanics of Queen Maud Land and parts of the Karoo Basalt of southern Africa. The rift between Africa and East Antarctica subsequently widened by seafloor spreading into the Weddell Sea and the Indian Ocean. 

Fig. 14.2 Queen (or Dronning) Maud Land contains groups of nunataks composed of the Jurassic Kirwan Volcanics. The groups of nunataks are identified by number 1, Vestfjella 2, Fossilryggen 3, Mannefallknausane 4, Heimefrontfjella 5, Bjornnutane 6, Sembberget and 7, Kirwan Escarpment. These groups of nunataks rise above the surface of the East Antarctic ice sheet which covers the entire area on this map (Adapted from Fig. 1 of Fumes et al. (1987))...

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