Tephra Layers in the Ice Sheets of Antarctica

Layers of ice containing disseminated particles of volcanic origin (i.e., tephra) are a common feature of blue ice areas and in the vicinity of volcanic vents in the Transantarctic Mountains. Volcanic tephra have also been found in the ice cores drilled at South Pole Station, Dome C, Vostock Station, and at Byrd Station, as well as in the glacial deposits that cover the floor of Wright Valley (Jones et al. 1973b Boger and Faure 1988). 

The chemical compositions of coarse tephra recovered from the core drilled at Byrd Station in West Antarctica are tightly clustered in the trachyte field of Fig. 17.44 

Takahe is a large shield volcano located about 500 km northeast of Byrd Station. It is composed of alkali-rich volcanic rocks ranging from basanite to trachyte. K-Ar dates reported by LeMasurier and Rex (1990) range from 0.31 0.09 Ma to less than 0.1 Ma. Although no fumarolic activity has been observed on Mt. Takahe, this volcano may have erupted less than 30,000 years ago. Four other volcanoes in Marie Byrd Land (Mt. Berlin, Mt. Sidley, Toney Mountain, and Mt. Waesche) are also potential sources of tephra in the Byrd-Station core, but were disqualified by Kyle et al. (1981) and Palais (1985a, b). Mt. Sidley is too old (4-5 Ma), Mt. Waesche and Toney Mountains are not 

The chemical composition of shards of volcanic glass from the 906-m core drilled dnring 1977/78 at Dome C (Lorius et al. 1979 Thompson et al. 1981) places them at point 5 in the trachyte field of Fig. 17.44. These particles originated from a depth of 726 m in the Dome-C core and were deposited about 25,000 years ago. Therefore, these tephra could also have originated from Mt. Takahe in spite of the great distance between Dome C and Mt. Takahe. The dispersion of tephra from Mt. Takahe may have been facilitated because the summit of this volcano is within 3,600 and 6,400 m of the boundary between the troposphere and the stratosphere. Therefore, the volcanic ash erupted by Mt. Takahe could have been injected directly into the stratosphere where it spread widely across Antarctica (Kyleetal. 1981). 

The ice core drilled in 1983/84 at South Pole Station contained a 3-mm tephra layer at a depth of 303.44 m (Palais et al. 1987). The tephra are composed of vesic-nlar glass with crystals of quartz, pyroxene, and pla-gioclase. The bulk chemical composition of these tephra plots close to the boundary between the andesite and benmoreite fields in Fig. 17.44 in strong contrast to the tephra in the cores at Byrd Station and Dome C (See also Koeberl 1990, Table 1). 

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