Diamictites, Transantarctic Mountains

Even more startling was the revelation by Heier et al. (1965) that the Tasmanian Dolerite and Granophyre contain excess radiogenic Sr indicated by an average initial Sr/ Sr ratio of 0.7115 0.0007. Mantle-derived basalts generally have significantly lower Sr/ Sr ratios than rocks in the continental crust because the ultramaflc rocks of the mantle have lower Rb/Sr ratios than granitic rocks of the continental crust. For example, the Sr/ Sr ratio of basalt on the island of Hawaii is 0.7043 (Faure 2001). 

The crustal characteristics of the Jurassic doler-ites of Antarctica and Tasmania relate these rocks to each other and set them apart from Jurassic dolerite in southern Africa and Brazil. This point was emphasized by Compston et al. (1968) in a direct comparison of Rb-Sr systematics of Mesozoic basaltic rocks in southern Victoria Land, Tasmania, South Africa, and South America. In addition, these authors reported K-Ar dates for plagioclase and pyroxene from a pegmatoid in the Lake Vanda sill in Wright Valley of southern Victoria Land. The results indicated a Middle Jurassic age for the Ferrar Dolerite, in agreement with the age of the Tasmanian Dolerite and the K-Ar dates of the Wisanger Basalt on Kangaroo Island of South Australia reported later by McDougall and Wellman (1976). 

The principal contribution by Compston et al. (1968) was to demonstrate that dolerites from several sills of Ferrar Dolerite in the Transantarctic Mountains have elevated initial Sr/ Sr ratios similar to the initial Sr/ Sr ratios of the Tasmanian Dolerite and the Wisanger Basalt on Kangaroo Island. These studies alerted other geologists to the challenge posed by the dolerite sills and basalt flows of the Transantarctic Mountains, Tasmania, and Kangaroo Island. The principal objectives of the research that followed were to  

Identify the magma sources and to explain the crustal geochemical signature of the basalt and dolerite of the Transantarctic Mountains. 

Explain the homogeneity of the chemical and isotopic compositions of these rocks. 

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Table 12.1 Deposits of diamictites and pyroclastics of the Ferrar Group in the Transantarctic Mountains...

In the Queen Alexandra Range of the Central Transantarctic Mountains diamictites and pyroclastic rocks of the Prebble Formation occur below the Kirkpatrick Basalt. The Prebble Formation overUes the felsic tuffs of the upper Falla Formation which Elliot (1996) renamed the Hanson Formation. Whole-rock samples of the tuff yielded a Rb-Sr date of 186 9 Ma corresponding to an Early Jurassic age (Faure and Hill 1978) which was later confirmed by Hammer and Hickerson (1994) based on the bones of tetrapod vertebrates. 

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