The weathering of granodiorite porphyry in the thiel mountains, inland antarctica

Abstract

The weathering of granodiorite porphyry is examined in the extremely cold and dry environment of the inland part of Antarctica. Weathering features include granular disintegration, rock varnish, and sheeting. Sheeting has gradually proceeded since the exposing of the nunatak, but the other types of weathering have not actively advanced in recent times.Granular disintegration primarily comprises the release of individual crystals. The mechanism of this release is that cracks are created along crystal boundaries and cleavages in phenocrysts mainly due to differential thermal expansion. Plagioclase and hypersthene are released more readily than quartz. Disintegration of plagioclase has produced many prism-shaped holes, 0.5 to 2.0 mm in length, while fine-grained quartz crystals, 0.05 to 0.1 mm in diameter, are incidentally released without cracking.The reddish brown (10R4/4) rock varnishes result from oxidation and consist of limonite, which fills cracks and penetrates into crystals. Ferrous iron in hypersthene, biotite, ilmenite and magnetite is transformed into limonite by oxidation. Manganese is not found in the varnishes. Sulfur, which is important for oxidation and which may have originated from adhered snow, is concentrated on the surface of the rock.Sheeting has precipitated rock falls, and has gradually formed a gray mosaic on the varnished wall. The sheeting was caused by gravitational body force, which is internal stress of the rock body due to the mass of the overburden.

Crack propagation by differential insolation on desert surface clasts

“…This is an especially pertinent case as there is a significant body of work analyzing the thermal state of rocks in polar regions (Hall, 1997(Hall, , 1998Lewkowicz, 2001;Hall and André, 2003). That thermal cycling could contribute to the breakdown of rocks is a natural assumption (for instance, Ishimaru and Yoshikawa, 2000) in areas known for significant freeze-thaw weathering and where permafrost has been seen to repeatedly fracture upon thermal contraction to form polygons. However, in those areas containing clasts made of consolidated rock and with ample sunlight, differential insolation may apply as well, especially if the cracking that occurs is directional in nature (for instance, French and Guglielmin, 2007).…”

Bacterial communities in Fe/Mn films, sulphate crusts, and aluminium glazes from Swedish Lapland: implications for astrobiology on Mars

“…Rock coatings are present in other cold environments; in particular, Al-, Si-, SO 4 -and Fe-rich rock varnishes have been observed in coastal (Victoria Land), inland Antarctica and Tibet (Glasby & Macpherson, 1981;Johnston & Cardile, 1984;Dorn et al 1992;Ishimaru & Yoshikawa, 2000;Giorgetti & Baroni, 2007;Krinsley et al 2009). …”

Quaternary bedrock erosion and landscape evolution in the Sør Rondane Mountains, East Antarctica: Reevaluating rates and processes

“…These features indicate that the coated surface generally reinforces the resistance against weathering but undergoes very slow, long-term salt weathering that produces microscopic cracks over a timescale of millions of years. The concentration of Fe and S in rock coating is also reported from the Thiel Mountains, an inland Antarctic mountain area (Ishimaru and Yoshikawa, 2000).…”