Kirwan Escarpment

The Kirwan Escarpment of Queen Maud Land at 73°25 S and 03°30 W in Fig. 14.2 consists of a large number of nunataks that are aligned along a northwest-facing 

1968) even though Neethling (1972a) reported that these nunataks are actually the peaks of a high mountain range that is buried in the East Antarctic ice sheet which is about 2.4 km thick on the inland side of the Kirwan nunataks. 

except at Tunga where the basalt flows are underlain by early Paleozoic quartzite of the Urfjell Group (Aucamp et al. 1972). 

Ladneset, Concretion Point, and Turnaround Ridge). The greatest thickness of basalt flows observed by Harris et al. (1990) is 460 m. 

The samples of basalt from nunatak B and from Tunga analyzed by Faure et al. (1979) were collected by A.P.H. Aucamp. The trace-element concentrations of these samples were later determined by Fumes et al. (1987) who also published trace-element concentrations of five basalt samples from Bjornnutane and three from Sembberget that were previously analyzed by Faure and Elliot (1971) and by Faure et al. (1972). 

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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))...

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...

Fig. 14.5 The initial Sr/ Sr ratios of the lava flows on nunat-aks B and Tunga of the Kirwan Escarpment have a polymodal distribution at 170 Ma. The principal mode is between 0.7040 and 0.7045. The wide range of variation of the initial Sr/ Sr ratios and their numerical values are relevant to the origin of these rocks (Data from Faure et al. (1979))...

Fig. 14.4 The variation of the concentrations of alkali metals and alkaline earths with increasing silica concentrations in the basalt flows of the Kirwan Escarpment is consistent with the effects of crystallization of Ca-rich plagioclase, olivine, and pyroxene from basalt magma. The concentrations of zirconium rise with increasing silica concentration as a result of progressive fractional crystallization in the magma chamber (Data from Harris et al. (1990))...

Fig. 14.6 Most of the basalt samples from nunataks B and Tunga in the Kirwan Escarpment scatter widely on the Rb-Sr isochron diagram. The only exceptions are three samples that define a straight line that yields a date of 181.9 0.4 Ma and an initial Sr/ Sr ratio of 0.70418 0.00000026 (2o). The samples that scatter above and below the line either formed from a heterogeneous magma that assimilated strontium from the Precambrian basement complex or they were altered after crystallization (Data from Faure et al. (1979))...

The most persuasive evidence for the contamination of the basalt flows on the Kirwan Escarpment arises from a Sr-Nd isotopic mixing diagram in Eig. 14.8 based on data by Harris et al. (1990). All data points were corrected for decay of the respective parent... 

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