Southern Nunataks

Formation. The beds dip to the northwest at about 50° and contain ripple marks. The quartzite beds are cut by quartz-feldspar veins that contain specular hematite. The age of these rocks is not known because they do 

Even more problematic is the hornblende migmatite on Spear Nunatak which is composed of layers of hornblende and of quartz-plagioclase (andesine) that have been folded and metamorphosed to the amphibolite facies (Fig. 7.7). Murtaugh (1969) considered the migmatites to be the oldest rocks in the Wisconsin Range and Minshew (1967) tentatively correlated them to the Nimrod Group of the Miller Range (Section 5.1.1). 

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Unfortunately, the basalt flows on the southern nunataks of Vestfjella (Fig. 14.10) cannot be dated by the whole-rock Rb-Sr method. The samples that were analyzed by Fumes et al. (1987) scatter on the Rb-Sr isochron diagram in Fig. 14.14a and do not define a unique straight line. Instead, we have drawn a reference line based on an assumed age of 170 Ma and an initial ratio of 0.70416 0.00021 (2a) which... 

The data for basalt <9from the southern nunataks of Vestfjella published by Fumes et al. (1987) scatter above and below the best-fit line in Fig. 14.15a. This line has a correlation coefficient of 0.60 and a positive slope of 0.2893. Nevertheless, the scattering of the data points means that these flows are not two-component mixtures. Instead, either they formed from magma that assimilated contaminants that had a range of Sr/ Sr ratios and strontium concentrations, or the rocks were altered after they crystallized, or both. 

The beds of the Taylor Formation exposed along the southern spur of Mt. Greenlee dip south at 40-70° and appear to reach a thickness of about 5.7 km. Additional outcrops of the Taylor Formation occur on Taylor Nunatak (84°44 S, 176°10 W) and on Waldron Spur which is located on the east side at the mouth of the Shackleton Glacier (Wade and Cathey 1986). 

Taylor Nunatak in Fig. 5.16 extends parallel to the ice-flow direction of the Shackleton Glacier for about 6 km and the elevation of its summit is 1,570 m. The rocks exposed in its nearly vertical slope that faces the glacier consist of ashfall tuffs, ashfall flows, and marble. The rocks have been folded into a large anticline indicated by a reversal of dip from 70° north at the northern end of the nunataks to 70° south at its southern end. However, the lithologic compositions of the north and south limbs do not match, perhaps because the structure is a fault rather than an anticline. The crest of the nunatak is covered by a sill of Ferrar Dolerite (Middle Jurassic) which is about 12 m thick. The Taylor Formation on Taylor Nunatak is composed of approximately equal proportions of... 

Hutson EE, Helper MA, Dalziel IWD, Grimes SW (1997) Initial results of geologic investigations in the Shackleton Range and southern Coats Land nunataks, Antarctica. Antarctic J US 32(5) 234-237... 

The Exposure Hill Formation occurs at the base of the sheet-like lava flows of Kirkpatrick Basalt that form the Mesa Range of northern Victoria Land and on nearby nunataks most of which are located in the Rennick graben in Fig. 12.6. The deposits of breccia and related pyroclastic rocks occur at Exposure Hill at the southern end of Gair Mesa and at Mt. Fazio and Scarab Peak on Tobin Mesa as well as on Mt. Carson adjacent to the Aeronaut Glacier in Fig. 12.7. hi addition, Elliot et al. (1986a) described a deposit of breccia on Agate Peak located about 26 km east of the northern tip of Pain Mesa (Fig. 12.6). 

Mesa Rmge, Monument Nunataks, LiteU Rocks, and related nunateiks in northern Victoria Land Prince Albert Mountains, Brimstone Peak, Allan Hills, and Carapace Nunatak in southern Victoria Land Westhaven Nunatak at the head of Hatherton Glacier in the Britemnia Remge... 

The Prince Albert Mountains in the northern part of southern Victoria Land consist of a large number of nunataks located on the polar plateau at the heads of Mawson, Harbord, and David glaciers aU of which flow into the Ross Sea. Several of these nunataks are composed of siUs of Ferrar Dolerite although flows of Kirkpatrick Basalt occur on Brimstone Peak (75°48 S, 158°33 E). Molzahn et al. (1996) reported isotope ratios of strontium, neodymium, and osmium as well as trace-element concentrations of five dolerite samples from the nunataks of the Prince Albert Mountains and two basalt samples from Brimstone Peak, including rubidium, strontium, samarium, neodymium, rhenium (Re) and osmium (Os). They also measured isotope ratios of strontium, neodymium, and lead in clinopyroxene and plagioclase of these rocks. 

The basal zone of the Basement sill on Roadend Nunatak Fig. 13.16 is enriched in MgO (Kibler 1981), presumably because of the presence of three pyroxenes including hypersthene. This zone is not present in the Peneplain sill which has a uniformly low MgO concentration of less than 7.0%. The Mg-enrichment of the Basement sill on Roadend Nunatak is similar to the MgO enrichment of the hypersthene-bearing sills in the ice-free valleys of southern Victoria Land reported by Gunn (1962, 1966) which was later attributed by Marsh and Philipp (1996) to flowage differentiation. 

Fig. 13.16 The lower part of the Basement sill on Roadend Nunatak has elevated concentrations of MgO up to 18.1% caused by the presence of hypersthene, pigeonite, and augite. Marsh and Philipp (1996) attributed the enrichment of the central sections of the Basement sill in the ice-free valleys of southern Victoria Land to flowage differentiation which concentrated the hypersthene crystals because of their greater size. The concentrations of MgO of the Peneplain sill are uniformly low at less than 7.0% arising from the presence of the clinopyroxenes (cpx), pigeonite and augite, whereas hypersthene (opx) is absent (Data from Kibler 1981)...

Fig. 13.27 The Sr/ Sr and Rb/ Sr ratios of whole-rock samples of the three dolerite sills on Mt. Achernar form erro-chrons that yield Middle Jurassic Rb-Sr dates based onX = 1.42 X 10 year However, several samples from each sill scatter above and below their respective errorchrons. The open circles are samples that were excluded from the age determination. Each sill has a different initial Sr/ Sr ratio all of which are lower than the initial Sr/ Sr ratios of the sills on Roadend Nunatak (Fig. 13.18) and in the ice-free valleys of southern Victoria Land (Fig. 13.6) (Data from Faure et al. 1991)...

The Cordiner Peaks are located about 15 km south of the southern end of the Dufek Massif (Fig. 13.41). This cluster of nunataks is composed of gently folded sedimentary rocks that characterize the Neptune Range of the Pensacola Mountains (Section 8.2.3) including the Gale Mudstone, the Dover Sandstone, and the sedimentary rocks of the Neptune Range of Paleozoic age (Schmidt and Ford 1969). These rocks were intruded by sills of the Ferrar Dolerite. 

Chemical Analyses of Dolerite Sills on Roadend Nunatak, Southern Victoria Land... 

The initial Sr/ Sr ratios reported by Harris et al. (1990) have a somewhat higher average than the basalt on nunatak B reported by Faure et al. (1979). Nevertheless, the initial Sr/ Sr and 1/Sr ratios of the eight freshest samples selected by Harris et al. (1990) out of a total of 26 also form a mixing line with a negative slope and a correlation coefficient of 0.79. These authors noted that a similar phenomenon occurs in the basalts of the Sabie River Formation (Karoo Group) in southern Lebombo (Cox and Bristow 1984). 

Fig. 14.19 The chemical types (CT) of flows and dikes on Plogen and Basen are defined in terms of concentration ratios of Ti/P vs. Ti/Zr (a) and Nb/Ta vs. Ti/Zr (b). The chemical compositions of CT-1 and CT-2 resemble certain basalt flows of the Karoo Group in southern Africa, whereas the CT-3 samples resemble the Kirwan Volcanics on the nunataks of southern Vestfjella. A fourth chemical type (CT-4) was later added by Luttinen et al. (1998) (Data and interpretation from Luttinen and Siivola (1997))...

Mt. Melbourne (2,732 m) in Fig. 16.27 is located at the northern end of the Terror Rift within the broad Victoria Land Basin which is a local manifestation of the Cenozoic West Antarctic rift system. The southern end of the Terror Rift is occupied by Mt. Erebus indicating that these two volcanoes are related by this rift. The Victoria Land Basin and the Terror Rift contain several submarine volcanic vents marked in Fig. 16.27. Mt. Melbourne in Fig. 16.28 is located on the coast of northern Victoria Land north of Terra Nova Bay. It is accessible by a short helicopter flight from the German and Italian research stations which are located about 20-30 km south of Shield Nunatak at the foot of Mt. Melbourne. Several other volcanic centers are located in the vicinity of Mt. Melbourne, including Cape Washington, Edmonson Point, Baker Rocks, and the Random Hills north of the central volcano. 

Wilson TJ (1995) Cenozoic transtension along the Transantarctic Mountains-West Antarctic rift boundary, southern Victoria Land, Antarctica. Tectonics 14(2) 531-545 Womer G, Orsi G (1992) Volcanic observations on Scott Island in the Antarctic Ocerm. Polarforschung 60 82-83 Womer G, Viereck L (1987) Subglacial to emergent volcanism at Shield Nunatak, Mt. Melbourne volcanic field, Antarctica. Polarforschung 57(1,2) 27-41... 

As time passed, the volume of the East Antarctic ice sheet increased sufficiently to bury the Transantarctic Mountains during the early Miocene until only the highest peaks remained ice-free as nunataks. At this time, the ice deeply eroded the valleys of the outlet glaciers and imposed on them the typical U-shaped cross-sections that are evident in the ice-free valleys of southern Victoria Land and elsewhere in the Transantarctic Mountains. More recently, the East Antarctic ice sheet thinned causing previously ice-covered areas of the Transantarctic Mountains to become ice-free and exposing till of the Sirius Group that was deposited by the ice sheet during its maximum extent. 

The tephra layers exposed on the ice fields west of the AUan HiUs were mapped by Dunbar (1995a, b) who also attanpted to date anorthoclase crystals contained within them by the Ar/ Ar method. The outcrop patterns of these tephra layers in Fig. 17.48 demonstrate their linear continuity and the structural deformation of the ice in this area. The same investigators also sampled dnst layers on other ice fields associated with the AUan HiUs, such as the ice around the Elephant and Redding moraines, the Ear Western, Ear Northern, and Meteorite City ice fields, ice adjacent to Carapace Nunatak, and other localities on the margin of the East Antarctic ice sheet in southern Victoria Land. 

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