Ice-Free Valleys

A third party consisting of Raymond Priestley, Bertram Army tage, and Sir Philip Brocklehurst explored the Ferrar Glacier and the ice-free valleys of southern Victoria Land west of Ross Island. Both parties were picked up by the Nimrod and, after Shackleton and his men had returned from their trek, the Nimrod headed north and landed safely in Lyttelton Harbor on the South Island of New Zealand. Ernest Shackleton was knighted by the King of England for his achievements in Antarctica, but his career of geographic exploration did not end there. 

Next, the Terra Nova took a four-man team led by Griffith Taylor across McMurdo Sound in order to explore the ice-free valleys of southern Victoria Land (Strange and Bashford 2008). The members of this team included Charles Wright, Frank Debenham, and Edgar Evans. 

Certain places in the ice-free valleys have been designated Sites of Special Scientific Interest (SSSIs), in order to protect ongoing scientific research or to preserve them in pristine condition for possible future study. This action was taken by the seventh Antarctic Treaty Consultative Meeting (ATCM VII) in 1972 and is contained in Recommendation VII-3 (Stonehouse 2002, p. 369). The SSSI sites in the ice-free valleys are Barwick Valley (Fig. 3.6), the area between the Canada Glacier and Lake Fryxell (Taylor Valley), and the Linnaeus Terrace... 

The basement rocks of the ice-free valleys of southern Victoria Land, including the area between the Ferrar and the Koettlitz glaciers farther south in Fig. 3.4, exemplify the structural complexity, lithologic diversity, regional metamorphism, and magmatic activity of... 

Ice-Free Valleys, Koettlitz Glacier, Southern Victoria Land... 

Metasedimentary rocks which are common in the ice-free valleys and in the Koettlitz-Skelton Glacier areas occur in the Brown Hills only as scattered inclusions within the Carlyon Granodiorite in the form of dark quartz-biotite-homblende schist and light-colored metaquartzite. A large raft of metasediment, about 10,000 m in area, occurs in the valley between the... 

Deutsch and Webb (1964) also reported an anomalously old date of 922 80 Ma for a feldspar concentrate and 979 80 Ma for a whole-rock sample from the same porphyry dike. These dates taken at face value suggested that this porphyry dike had crystallized about 1,000 million years ago, which implied that the basement rocks in the ice-free valleys had... 

Smithson SB, Fikkan PR, Murphy DR, Houston RS (1971b) Development of augen-gneiss in the ice-free valley area, south Victoria Land. In Adie RJ (ed) Antarctic geology and geophysics. Universitetsforlaget, Oslo, Norway, pp 293-298... 

The Priestley Formation of the Deep Freeze Range does not correlate with the metasediments of the Robertson Bay Terrane, contrary to a proposal by Nathan and Skinner (1972) who, at that time, had not yet visited the type locality of the Robertson Bay Group in Edisto Inlet (Skinner 1983). It seems more likely that the Priestley Formation is the local representative of the Koettlitz Group of southern Victoria Land because it occupies the same stratigraphic position as the Asgard Formation in the ice-free valleys of southern Victoria Land (McKelvey and Webb 1962 Section 3.1.2) and because both formations contain sedimentary carbonate beds. However, this conjecture has not been confirmed or even tested. 

These isotopic data combined with the chemical compositions published by Borg et al. (1986) strongly support the conclusion that the Granite Harbor Intrusives of northern Victoria Land are S-type granitoids. This conclusion applies also to the Wright and Vanda Intrusives of the ice-free valleys of southern Victoria Land and perhaps to some of the Cambro-Ordovician granitic plutons elsewhere in the Transantarctic Mountains. 

The geologists who accompanied Robert Scott and Ernest Shackleton to Antarctica were amazed when they entered the mountains of southern Victoria Land and discovered the ice-free valleys such as Wright Valley in Fig. 10.1 (Sections 1.4, 2.3, and 3.1). The modem traveler entering the ice-free valleys by helicopter from McMurdo is similarly affected because the wide U-shaped valleys present a familiar view of sandy plains dotted with lakes and ponds filled with liquid water and of meltwater streams that flow from alpine glaciers descending from the high mountain ranges that frame these valleys. 

The first scientific desaiptions of the Beacon rocks in the ice-free valleys were published by Ferrar (1907), David and Priestley (1914), andDebenham (1921) followed after the IGY by Webb and McKelvey (1959), McKelvey and Webb (1959, 1961, 1962), Hamilton and Hayes (1960,1963), and Zeller et al. (1961). These reports were followed by the papers of Gunn and Warren (1962), Angino et al. (1962), Allen (1962), Allen and Gibson (1962) Harrington and Speden (1962), Shaw (1962), and Vialov (1962). In the following year, Webb (1963) published the first comprehensive... 

We now move south from the ice-free valleys and the Boomerang Range to the Darwin Mountains of southern Victoria Land adj acent to the Darwin and Hatherton glaciers and north of the Byrd Glacier in Fig. 10.8. This segment of the Transantarctic Mountains also includes the Brown Hills (Section 3.3) where granitic rocks of the local basement complex are exposed. 

Fig. 13.8 The concentrations of silica and of alkali metals of the sills of Ferrar Dolerite in the ice-free valleys of southern Victoria Land place these rocks into the quartz dolerite and diorite fields. The high concentrations of silica and low content of alkali metals also identify these rocks as subalkalic quartz-normative tholeiites. The rocks are classified as dolerites because they are primarily composed of calcic plagioclase and pyroxenes with ophitic texture. The Ferrar Dolerite closely resembles the Kirkpatrick Basalt in terms of chemical composition and mineralogy, but differs by its ophitic texture and intrusive mode of occurrence. Accordingly, dolerite sills and basalt flows are assumed to have formed from the same mafic magma (Data from Hamilton 1965)...

Marsh and Philipp (1996) reported that the concentrations of MgO in vertical profiles of the Basement sill in the ice-free valleys of southern Victoria Land increase up-section toward peak values before decreasing higher up in the sill. Gunn (1966) had previously observed this pattern and noted that it was caused by the vertical distribution of hypersthene which occurs only in the center of the Basement sill, whereas augite... 

Fig. 13.12 The central part of the Basement sill in the ice-free valleys of southern Victoria Land is enriched in MgO. The Mg-enrichment coincides with the distribution of hypersthene ((Mg, Fe)2Si20g) in addition to Mg-bearing augite (Ca(Mg,Fe, Al) (Al,Si)20g) and pigeonite (Ca,Mg,Fe silicate) (Gunn 1966). The accumulation of coarsely crystalline hypersthene in the middle of the Basement sill was attributed by Marsh and Philipp (1996) to flowage differentiation (Adapted from Fig. 2 of Marsh and Philipp 1996)...

The sedimentary rocks of the Beacon Supergroup north and south of the ice-free valleys of southern Victoria Land contain an abundance of intrusive dolerite sills of the Ferrar Group. The sills are not popular with stratigraphers and paleontologists because they interrupted the continuity of the exposures of the Beacon rocks and caused contact metamorphism of reactive sedimentary rocks that contain diagnostic fossils. 

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 profiles of SiO, MgO, and Na O in Fig. 13.36 reveal that the concentrations of these elements vary only within narrow limits, except for the lower chilled contact described above. The concentration of SiOj decreases up-section from about 54% to 52%, but the trend reverses at about 100 m above the base of the sill and the concentrations of SiOj increase in the upper 30 m toward 54%. The concentration of MgO ranges from about 6% to 7% and includes only local variations. This profile indicates that the sill at Portal Rock does not contain a hypersthene zone as do the dolerite sills in the ice-free valleys of southern Victoria Land (Gunn 1962 1966). The concentrations of NajO remain virtually constant throughout the body of this sill contrary to the expectation that the crystallization of early-formed anorthite enriched the residual magma in Na O and caused the plagioclase to become enriched in the albite conponent. 

The Cenozoic volcanic rocks of the Transantarctic Mountains are collectively referred to the McMurdo Volcanic Group. These rocks were erupted by volcanoes located in four volcanic provinces described in this chapter. The Erebus volcanic province includes Mt. Erebus, Mt. Terror, and Mt. Bird on Ross Island as well as Mt. Discovery and Mt. Morning on the mainland of southern Victoria Land. Volcanic rocks of Cenozoic age occur widely on the other off-shore islands as well as on Minna Bluff, the Brown Peninsula, the Royal Society Range, and the ice-free valleys. 

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. 

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