Pioneers Escarpment

Exploration

The escarpment was photographed from the air by the U.S. Navy, 1967, and was surveyed by British Antarctic Survey (BAS), 1968–71. It was named "Pioneers Escarpment" by the United Kingdom Antarctic Place-Names Committee (UK-APC) because features on the escarpment are named after the pioneers whose inventions have assisted living and traveling conditions in the polar regions. The escarpment was visited and the rocks sampled extensively for the first time during the Geologische Expedition in die Shackleton Range (GEISHA) expedition in 1987–88.

Geology

The outcroppings in the escarpment typically contain a succession of sedimentary rocks and rocks of volcanic origin which make up the Pioneers Group, a subcrustal unit. The metamorphic rocks of the Pioneers Group are a diverse series of metasedimentary rocks. Rock types include quartzites, mica schists, Al-rich schists and gneisses, calc-silicate schists, metalimestones and marbles, and amphibolites.

Most of the rock types found in the escarpment are metamorphosed from amphibolite facies, but cores of garnet contain traces of granulite facies. The metasedimentary rocks are from deposits that were laid down in shallow water on the submerged rim of a craton. During the peak of metamorphism both the sediments and the volcanics were subject to high pressures but relatively low temperatures of around 600 C. At this time they would have been as deep as 35 km, but were probably uplifted before the Ross orogeny 500 million years ago. Additional sedimentation occurred after this, creating non-metamorphic shales, sandstones and greywackes that may date to the Jurassic (200–145 million years ago).

Features

Features of the escarpment and neighboring nunataks that are named on the 1983 United States Geological Survey map are (northwest to southeast):

Jackson Tooth

Main article: Jackson Tooth

Nunatak rising to 1,215 m at the west end of Pioneers Escarpment, Shackleton Range. In association with the names of pioneers of polar life and travel grouped in this area, named by the UK-APC in 1971 after Major Frederick George Jackson (1860-1938), English Arctic explorer who in 1895 designed the features of the pyramid tent, later to become standard equipment on British polar expeditions.

Jackson Tooth has a visible band about 50 m thick of medium grained marble, coloured light grey to white, containing tremolite. Below this is a band about 100 m thick of grey marble, with up to 10% of its volume made up of star-like aggregates of chrysotile-asbestos. There may also be muscovite schists and muscovite quartzite holding accessory tourmaline, since rocks like this are seen about 2 km north of the nunatak.

M'Clintock Bastion

Main article: M'Clintock Bastion

The main rock types on M'Clintock Bastion are tremolite marble, garnet-two-mica schist and staurolite-garnet-muscovite schist.

Mount Kelsey

Spaeth Nunatak

Spaeth Nunatak is on the 1600 m contour line about 10 km south.south-west of Blanchard Hill. Rock types include impure marble which sometimes contains layers of quartzite. The coarse grained marble in other places includes rounded olivines, partly serpentinized, with chondrodite, opaque minerals and quartz. This marble has a high concentration of strontium, up to thirty times more than in other marbles of the Shackleton Range.

Meade Nunatak

Main article: Meade Nunatak

Rocks exposed on the Meade Nunatak experienced two metamorphic overprints around 1700 and 500 million years ago. The northern part of Meade Nunatak contains epidote-biotite-plagiocIase gneiss and epidote-biotite amphibolite. The amphibole has a texture that may indicate it has replaced cIinopyroxene. In the southern part of the nunatak there is biotite quartzite, biotite schist, garnet-biotite schist, plagiocIase gneiss with a small mica content, and plagiocIase-quartz-mica schists, There are also garnet-kyanitestaurolite-mica schists, staurolite-garnet-plagiocIase gneiss and perhaps a kyanite-quartzfels.

Blanchard Hill

Main article: Blanchard Hill

The hill holds a garnet-mica schist and biotite-garnet-amphibole schist, which is intensely folded, and to the northwest is thrust up onto an intensely folded sequence of quartzite with layers 20 m thick holding beds about 40 cm thick of light grey calciphyre.

Olesch Nunatak

Olesch Nunatak is about 4.5 km west.south-west of Whymper Spur. Rock types include a quartz-carbonate rock or carbonate-bearing quartzite, a garnet-two-mica schist and a garnet-hornblende-biotite schist.

Whymper Spur

Main article: Whymper Spur

Whymper Spur has a layer about 80 to of marble with intercalated amphibolite mostly in boudins. The marble is a tremolite marble or a silicate marble containing cIinopyroxene and/or tremolite aggregates.

Weissenstein

Weissenstein (White Spur) is an outcrop halfway between Mummery Cliff and Whymper Spur. It is composed of a very pure, even-grained, white marble. It is named for its white appearance.

Mummery Cliff

Main article: Mummery Cliff

Rock types include garnet-two-mica gneiss.

Aronson Corner

Main article: Aronson Corner

Aronson Corner rock types include metacarbonate with metaquartzite. Dark grey caleiphyres (phlogopite-tremolite-diopside marble) are found with quartz-tremolite rocks.

Mount Dewar

Main article: Mount Dewar

Mount Dewar rock types include fine-grained fuchsite quartzite, with a very low proportion of mica, which occurswith amphibolite (as in Sauria Buttress) and microcline gneiss.

Chevreul Cliffs

Main article: Chevreul Cliffs

Chevreul Cliffs have marble with light green to yellow stains and wollastonite. A two-mica schist shows evidence of postcrystalline deforrnation. Some layers in the schist contain epidote and hornblende.

Lundström Knoll

Main article: Lundstrom Knoll

Lundström Knoll has a two-mica gneiss that partly shows augen gneiss texture.

Sauria Buttress

Main article: Sauria Buttress

Sauria Buttress has thick beds of quartzite containing fuchsite, which gives the quartzite a pale green appearance. The metamorphosed sandstone alternates with amphibolites.

Neighboring isolated features

Lord Nunatak

Main article: Lord Nunatak

Rocks exposed on Lord Nunatak experienced a Pan-African metamorphic event around 515–500 million years ago. Rock types include amphibolite, which was probably derived from an igneous rock. There are higher than usual concentrations of chromium, nickel and iron, so the parent rock may be a basic igneous rock such as basaltic komatiite. The nunatak also has gamet amphibolite and hornblende schists.

Baines Nunatak

Main article: Baines Nunatak

Rock types include garnet-two-mica schist and hornblende-garnet-plagioclase gneiss.

Notes

References

Sources

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