| Remote Sensing and structural aspects
of two Australian impact structures: Strangways (N.T.) and Shoemaker (W.A.)
Contact: Heiko Zumsprekel, Geologisch Paläontologisches Institut, Corrensstr. 24, D-48149, Tel.: +49-(0)251-83-33908, zumspre@uni-muenster.de
The Strangways Structure (15°12' S/133° 35' E) is located ca. 75 km southwest of Elsey Station near Mataranka (N.T.) in a relatively remote area. Guppy et al. (1971) first identified the impact origin of the circular structure. The impact occured into Meso- to Neoproterozoic, clastic sedimentary rocks of the lower Roper Group, but also affected the underlying granitic basement. The central uplift area (ca. 25 km in diameter) is the best exposed part of the Strangways Structure, while the outer parts of the crater (collapse zones and crater rim) are concealed beneath Cainozoic, Cambrian, and Cretaceous rocks. Estimated diameters of the total crater range from 26 to 40 km. Formerly believed to be of Phanerozoic age, new Ar/Ar data (Spray et al., 1999) and structural field observations (Shoemaker and Shoemaker, 1996) clearly suggest a Proterozoic age (ca. 680 Ma). Considering this age, the Strangways Structure is relatively slightly eroded and represents one of the few Proterozoic structures in which impact melt rocks and melt breccias have been preserved. The Shoemaker Impact Structure is regarded as the oldest known Australian impact structure to date (ca. 1630 Ma, Shoemaker and Shoemaker, 1996). Approximately 30 km in total size, the crater is located in the arid, central part of Western Australia (25° 52', 120°, 53', near Wiluna). The target rocks consist of Archean granitic basement and the lowermost part of the sedimentary, Palaeoproterozoic Earaheedy Group (1800 - 1700 Ma). The outer margin of the structure can be clearly traced in satellite images and aerial photographs by the circular arrangement of banded iron formations. As the structure has been eroded below its original crater floor (no impact melt or melt breccias have been preserved), it reveals a unique view into a deeper level of a complex impact structure. Remote sensing/GIS approach The remote sensing analysis and GIS processing of the two meteorite craters is based on the following data background:
Field work Field investigations have been carried out during the field season of 1999 and focused on References Guppy, D.J., Brett,R.
& Milton, D.J. (1971): Liverpool and Strangways Craters, Northern
territory. Two structures of probable impact origin. - J. Geophys. Res.
76,
5387-5393.
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In
Australia numerous impact structures of probable or known Precambrian
age have been recognized by remote sensing and following field investigations
during the last years (Shoemaker and Shoemaker, 1996). The good
preservation of these ancient meteorite craters on the Australian continent
is mainly due to two factors: the excellent exposition of moderately deformed
and largely unmetamorphosed Proterozoic sedimentary rocks, and the fairly
structural stability of the Australian craton throughout Earth's history.
Besides, the identification of impact structures is favored by (semi)arid
climate conditions in most parts of inner Australia.