Isotopic Age Determinations

Van Schmus et al. (1997) also dated zircons and monazites from the Granite Harbor Intrusives of the Leverett Glacier area. The results in Table 6.8 generally confirm that the intrusion of these plutons occurred after the eruption of the volcanic rocks of the Leverett Formation. The analytical data also indicate that some of the samples contain old xenocrystic 

The U-Pb dates of zircons in granites on ML Webster and in the Berry Peaks (494 3 and 480 5 Ma, respectively) indicate that the age of these granites is Early Ordovician and that they crystallized at the end of the Ross Orogeny. The gneisses in the Fallone Nunatak contain old xenocrystic zircons that may have been derived from Neoproterozoic Grenville basement that could have existed in the crustal magma sources off-shore of the paleo-Pacific coast of the present Transantarclic Mountains (McKenna etal. 1994 Dalziel 1992). 

The geologic history of the basanent rocks of the Queen Maud Mountains is recorded by the volcanosedimentary complex which has beai preserved at several 

Geologic unit Location Concordia Intercept dates (Ma) Upper Lower 

Quartz-porphyry metarhyolite, Cressey Peak, Harold Byrd Mountains 519 4 31 53 

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Krogh T. E. (1971a) A low contamination method for the decomposition of zircon and the extraction of U and Pb for isotopic age determinations. Carnegie Inst. Wash. Yearb. 70, 258-266. 

Fig. 3.20 The isotopic age determinations reviewed in this chapter were used to reconstruct the geologic history of the basement rocks of the Transantarctic Mountains in southern Victoria Land...

Isotopic age determinations of the basement rocks of the Terra-Nova-Bay area are listed in Appendix 4.8.1 based primarily on the work of Kreuzer et al. (1981, 1987), Vetter et al. (1984), Borsi et al. (1988), Armienti et al. (1990), and Adams (2006). The whole-rock Rb-Sr dates reported by Armienti et al. (1990) prove that the age of the Granite Harbor Intrusives of the Deep Freeze Range is Middle Cambrian based on the time scale of the lUGS (2002). All of the whole-rock samples they analyzed define a straight line in Fig. 4.8 that yields a date of507 7 Ma and an initial Sr/ Sr ratio of 0.71034 0.00022. 

Wade and Cathey (1986) also reported isotopic age determinations of feldspar and biotite of the Hope Granite by the K-Ar and Rb-Sr methods. However, feldspars do not retain radiogenic " Ar and the initial Sr/ Sr ratios used to calculate the Rb-Sr dates were not provided. Therefore, the reliability of these dates is uncertain. However, two Rb-Sr dates of biotite from Longhorn Spurs (84°40 S, 174°4LW) and Den Hartog Peak (84°20 S, 178°52 E) indicate that the granitic rocks at these locations cooled sufficiently to retain radiogenic Sr at 470 25 Ma during the Ordovician Period. 

McLeUand (1967) reported two isotopic age determinations for biotites of the Lonely Ridge Granodiorite (Mirsky 1969) ... 

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. 

In addition, the turbidite basement complex of the Neptune Range is unconformably overlain by the Middle Cambrian Nelson Limestone which is absent from the Schmidt and Williams hiUs. Therefore, the age of the turbidites that underlie the Nelson Limestone in the Neptune Range must be pre-Middle Cambrian , whereas the turbidites in the Schmidt and Williams Hills where the Nelson Limestone are absent are post-Middle Cambrian in age as confirmed by isotopic age determinations. This confusing situation was resolved... 

Table 8.5 Summary of isotopic age determinations by Zeh et al. (1999) of the Haskard Highlands, Shackleton Range...

Table 8.6 Siunmary of isotopic age determinations from the La Grange Nunataks, Shackleton Mountains ...

Summary of Isotopic Age Determinations of the Basement Rocks of the Thiel Mountains (Schmidt and Ford 1969 Eastin 1970 Pankhurst et al. 1988)... 

Isotopic Age Determinations of Granitic Rocks in Whitmore Mountains and Other Nunataks of the Eiisworth-Whitmore Mountains Block... 

Selected Isotopic Age Determinations of Rocks and Minerals in the Pensacola Mountains in Units of 10 Years (Ma) ... 

Aaron JM, Ford AB (1964) Isotope age determinations in the Thiel Mountains, Antarctica. Geological Society of America, Special Paper 76, Abstracts for 1963, p. 1... 

Table 9.1 Isotopic age determinations of the Littlewood and Bertrab nunataks in Coats Land and of the Haag Nunatak of West Antarctica ...

In spite of the uncertainty of the isotopic age determinations, the mafic igneous rocks that were formed during the initial split between East Antarctica and Africa constitute the largest known volume of rift-related magma in the world. 

The former association of Marie Byrd Land (MBL) with northern Victoria Land (NVL) was tested by isotopic age determinations of the Swanson Formation in the Ford Ranges located east of Edward Vn Peninsula in MBL (Adams 1986 Adams et al. 1995). The Swanson Formation consists of folded metasedimen-tary rocks that were intruded by granitoids of Late Devonian age and by leucogranites of Jurassic to Cretaceous age. These plutons are surrounded by contact metamorphic aureoles of biotile homfels that are 100-500 m wide. The pre-Devonian deformation of the Swanson Formation was accompanied by low-grade regional metamorphism of the rocks. 

The principle of isotopic age determination is used in food analysis. Radiocarbon analysis can be used to detect whether a product is of natural or synthetic origin. The absence of in the sample would indicate a synthetic origin, while the presence of indicates a natural origin. The determination of tritium contents can be used, e.g., to determine the age of wine. 

Bridgewater D. Isotopic age determinations from South Greenland and their geological setting. Bull. Groenl. geol. Unders. 53, 1965, 56 p. 

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