Tasmanian Dolerite

The similarity of the Upper Division of the Parmeener Supergroup to the Permo-Triassic rocks of the Beacon Supergroup is unmistakable, but correlations 

Faure and T.M. Mensing, The Transantarctic Mountains Rocks, Ice, Meteorites and Water, DOI 10.1007/978-90-481-9390-5 12, Springer Science-l-Business Media B.V. 2010 

The sedimentary rocks of the Upper Permeenar Group were intruded by sills and dikes of the Tasmanian Dolerite and the Red Hill (jranophyre. K-Ar age determinations of the sills by Schmidt and McDougall (1977) yielded an average date of 170.5 8.0 Ma which corresponds to an early Middle Jurassic age. 

The Tasmanian Dolerite forms several thick transgressive sills and dikes. The dike at Red Hill is up to 1,600 m wide and grades from tholeiite at depth to granphyre at the top. McDougall (1962) used chemical, petrographic, and mineralogical evidence to show 

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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 ... 

All of the evidence concerning the chemical and isotopic composition of the Tasmanian Dolerite and of the Kirkpatrick Basalt in the Transantarctic Mountains... 

Tasmanian Dolerites (open circles) cluster in quadrant 4 of the Sr-Nd isotopic mixing diagram which is partitioned based on the isotopic composition of the Chondritic Uniform Reservoir (CHUR) described by Faure and Mensing (2005). The diagram also contains data points (crosses) of contact sediment which define an... 

The initial Sr/ Sr and Nd/ Nd ratios of Kirkpatrick Basalt in the Mesa Range of northern Victoria Land in Fig. 12.39 occupy an area in quadrant 4 close to the data cluster of the Tasmanian Dolerite. Therefore, this Sr-Nd isotope mixing diagram confirms... 

The paleomagnetism of the Tasmanian Dolerite was determined by Schmidt and McDougall (1977) while Valencio et al. (1979), Valencio (1979), and Vilas and Valencio (1979) compared the paleomagnetic properties of Mesozoic and Cenozoic igneous rocks in Antarctica, South Africa, and South America. A memorial to Dr. Daniel A. Valencio was published by Anonymous (1991). 

Hergt JM (1987) The origin and evolution of the Tasmanian Dolerites. Ph.D. dissertation, Australiem National University, Canberra, Australia... 

Schmidt PW, McDougaU I (1977) Palaemagnetic and potassium-argon dating studies of the Tasmanian Dolerites. J Geol Soc Australia 25(Pt. 6) 321-328... 

Fig. 13.4 The K-Ar dates of plagioclase rind pyroxene (diagonal lines) of dolerite siUs in southern VLctoiia Land measured by McDougall (1963) ranged fiom 147 to 163 Ma. Subsequently, Compston et al. (1968) published additional K-Ar dates of these minerals (shaded) between 153.9 and 169.2 Ma. The oldest dates indicate that the age of the Ferrar Dolerite is Middle Jurassic (160-180 Ma) based on the timescales of Kulp (1961) and of the lUGS (2002). These results also agree with the K-Ar dates of the Tasmanian Dolerites reported earlier by McDougall (1961,1962)...

Fig. 13.6 The initial Sr/ Sr ratios of the Ferrar Dolerite in the Transantarctic Mountains have a mean of 0.71124 0.00041 (la) that is identical to the average initial " Sr/ Sr ratio of the Tasmanian Dolerite when both data sets are corrected to 170 Ma and X=lA2x 10 year These isotope ratios are characteristic of granitic rocks in the continental crust in spite of the fact that the chemical composition of the dolerites indicates that the basalt magma from which they formed originated in the mantle beneath the continental crust (Data for the Ferrar Dolerite from Compston et al. 1968 Jones et al. Tasmanian Dolerite data from Heier et al. 1965 Hergt et al. 1989a)...

Heier KS, Compston W, McDougall I (1965) Thorium and uranium concentrations, and the isotopic compositions of strontium in the differentiated Tasmanian dolerites. Geochim... 

McDougall I (1962) Differentiation of the Tasmanian Dolerites Red HUl Dolerite-Granophyre association. Geol Soc Amer Bull 73 279-316... 

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