Basement Rocks, Wisconsin Range

The basement rocks of the Wisconsin Range in Fig. 7.4 are similar to those of the Queen Maud Mountains (Chapter 6) and are generally correlated with the 

LaGorce and Wyatt formations and with the Granite Harbor Intrusives. Sills and dikes of the Ferrar Dolerite are rare in the Wisconsin Range, in contrast to the Transantarctic Mountains between southern Victoria Land and the Amundsen Glacier where numerous dolerite sills occur within the Beacon Supergroup. 

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Geologic History of the Basement Rocks, Wisconsin Range ... 

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... 

With the probable exception of the hornblende migma-tite on Spear Nunatak (Section 7.2.3), the phylUtes and metagraywackes of the LaGorce Formation are the oldest rocks in the basement of the Wisconsin Range. 

Fig. 7.11 Whole-rock Rb-Sr age determinations of the LaGorce Formation in the basement complex of the Wisconsin Range of the Horlick Mountains (Data from Montigny and Faure 1969 Faure unpublished in Appendix 7.8.2.1)...

Fig. 7.13 Whole-rock Rb-Sr age determinations of granitiod basement rocks in the Wisconsin Range (Data from Faure...

Table 7.2 Summary of Rb-Sr dates of whole-rocks and mineral concentrates from the basement rocks of the Wisconsin Range and the Long Hills in the Horlick Mountains. Recalculated to X ( Rb) = 1.42 x 10 year from unpublished analytical data by Faure et al.

Fig. 7.17 Summary of age determinations by the Rb-Sr method of basement rocks of the Wisconsin Range in the Horlick Mountains. Dates from Figs. 7.11-7.16...

This Early Cambrian date is compatible with the stratigraphy and age determinations of the basement rocks of the Wisconsin Range. However, the severe alteration of the Todd Ridge pyroclastics casts doubt on the reliability of this date. 

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. 

The rocks exposed in the Thiel Mountains belong to the basement complex of the Transantarctic Mountains. The sedimentary rocks of the Beacon Supergroup that uncon-formably overlie the basement rocks elsewhere in the Transantarctic Mountains do not occur in the Thiel Mountains either because they have been removed by erosion or because they were not deposited there. The stratigraphy of the basement rocks of the Thiel Mountains in Table 8.1 is deceptively simple compared to the basement rocks elsewhere in the Transantarctic Mountains (e.g., the Queen Maud Mountains and the Wisconsin Range). 

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... 

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