Granitic Basement

The granitic basement and the overlying rocks of the Beacon Supergronp as well as the Ferrar Dolerite sill are cut by normal fanlts of post-Middle Jurassic age (Long 1965). However, the location of these faults is obscured by snow and ice except locally on the 

The first description of the granitic rocks of the basement complex by Long (1961) was illustrated by 

I I Mt. Glossopteris Fm. Discovery Ridge Fm, Buckeye Tillite I I Horlick Fm. 

Isotopic age determinations by the Isotope Geology Branch of the US Geological Survey reported by Treves (1965) indicate cooling ages of 472 24 Ma (K-Ar, biotite. Discovery Ridge) and 471 49 Ma (Rb-Sr, feldspar, Treves Butte) and a crystallization age of 516 72 Ma (Rb-Sr, whole rock, Treves Butte) for the porphyritic quartz monzonite. These dates are compatible with the geologic history of the basement rocks of the Wisconsin Range in Fig. 7.17. 

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This work is a part of a European research program initiated at the Soultz-sous-Forets site (France) in 1987 which aims to develop a pilot plant for extracting heat accumulated in the deep fractured granitic basement. Heat extraction must be carried out by forced circulating of a fluid between three wells drilled at S km depth. 

Fig. 6.5 The western edge of the southern part of the Nilsen Plateau along the Amundsen Glacier contains small outcrops of metavolcanic and metasedimentary rocks of the basement complex that were intruded by the Granite Harbor suite. McLelland (1967) divided the granitic basement rocks into the Cougar Canyon Quartz Monzonite, the Lonely Ridge Granodiorite, the North Quartz Monzonite, and the South Quartz Monzonite which are not differentiated on this map. The basement rocks are unconformably overlain by sandstones of the Beacon Supergroup and sdUs of Ferrar Dolerite (Adapted from McLelland 1967)...

Fig. 7.1 The north-facing escarpment of the Wisconsin Range of the Horlick Mountains is composed primarily of granitic basement rocks. This photograph was taken on January 9,1965,...

The granitic basement rocks of the Wisconsin Range Batholith are the dominant lithology in the Quartz Hills and Caloplaca Hills west of Reedy Glacier (Fig. 7.4). They also form the main part of the exposed basement rocks east of the Reedy Glacier and extend east as far as the Long Hills. These granitic basement... 

Fig. 7.14 Whole-rock Rb-Sr age determinations of porphyritic and unfoliated granitic basement rocks in the Wisconsin Range (Data from Montigny and Faure 1969 Faure unpublished in Appendix 7.8.2.4)...

Modal Compositions of the Granitic Basement Rocks, Ohio Range (Long 1961 Treves 1965)... 

Fig. 8.3 The crystallization age of the granitic basement rocks of the Thiel Mountains was calculated from analytical data of Eastin (1970) listed in Appendix 8.5.3. The rock samples were provided by Arthur B. Ford. Solid circles = quartz monzonite open circles = biotite granite. One of the five samples ( 499) analyzed by Eastin (1970) was excluded because it lost radiogenic Sr. The value of the decay constant of Rb used to calculate the date from the slope of the isochron was A = 1.42 x 10 " year A The slope and intercept of the isochron were determined by unweighted linear regression...

Knob (499 A.B. Ford 7.12 61.64) which had lost radiogenic Sr. The four remaining samples of granitic basement rocks closely define an isochron in Fig. 8.3 that yields a date of 530 6 Ma and an Sr/ Sr ratio of 0.71153 0.00057 (la). This date and the initial Sr/ Sr ratio associate the granitic rocks of the Thiel Mountains with the Granite Harbor Intrusives and thereby indicate that this remote mountains range is an extension of the Transantarctic Mountains. 

Minshew (1966, 1967) reported that the Buckeye Formation in the Wisconsin Range is predominantly a tillite, 80-110 m thick, that rests unconformably on the granitic basement which is striated, grooved, and polished (Fig. 7.10). The lower part of the Buckeye Tillite... 

Glacier), and on granitic basement rocks in the Queen Maud Mountains between the Shackleton Glacier and the Wisconsin Range. In the Ohio Range, the Buckeye TiUite rests discon-formably on the Devonian Horlick Formation (Adapted from... 

Fig. 13.1 The Wright Valley in southern Victoria Land contains three sills of Ferrar Dolerite The Basement sill intruded the Granite Harbor Intrusives of the local basement, the Peneplain siU lies between the granitic basement and the overlying sandstones of the Beacon Supergroup, and the uppermost sill was injected...

Trachyte occurs at Mt. Cis between Cape Royds and Cape Evans. It is oversaturated with respect to silica (i.e., it is quartz normative) and contains abundant inclusions (Thomson 1916 Jensen 1916 Treves 1967). The inclusions consist of sanidinite, pyroxene granulite, diabase, and metamorphosed sandstone. These inclusion suggest that Ross Island may be underlain by granitic basement rocks. Beacon sandstones, and perhaps even by Ferrar Dolerite. 

We prefer the second alternative because the Sr/ Sr ratios of most Cenozoic lavas analyzed by Stuckless and Ericksen (1976) and by Jones and Walker (1972) provide no evidence that the magma was contaminated by strontium derived from the granitic basement rocks. The only exception is the sample of trachyte (CC-82, Fig. 16.7) which has a high Sr/ Sr ratio of 0.70501 (Stuckless and Ericksen 1976). 

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