Mathematics – Logic
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.582s&link_type=abstract
Meteoritics, vol. 30, no. 5, page 582
Mathematics
Logic
3
Basin Rings, Basins, Population, Crust, Bombardment, Impact Basins, Moon
Scientific paper
Multi-ring basins (impact craters greater than 300 km in diameter, regardless of presently expressed morphology; [1, 2]) are of primary importance in the excavation and redistribution of crustal materials and serve as the loci for the accumulation of extruded lavas on the Moon. Understanding their distribution and configuration is important in order to reconstruct the basin-forming impact [2]. The Clementine mission has made the first global maps of the Moon, including altimetry from a laser ranging experiment [3, 4]. This map permits the characterization of long-wavelength topographic features of the lunar crust, including the most prominent and important features, multi-ring basins. We have now surveyed the entire Moon with laser altimetry data from Clementine and have inventoried the global basin population. Many of the most obscure and degraded basins are strikingly expressed in the topographic data. Basins such as Mendel-Rydberg, a nearly obliterated ancient basin (600 km diameter, 5 km deep) south of Orientale, displays nearly as much relief as the "pristine" Orientale basin (900 km diameter; 7 km depth) [5]. The Fecunditatis basin, an obscure quasi-circular feature south of Mare Crisium [3], displays considerable topographic prominence, including an average relief of about 5 km. However, not all of the ancient basins are so deep: the Mutus-Vlacq basin [3], south of Nectaris, is clearly visible in the altimetry [5], but is only 1 to 1.5 km deep. Other basins that appear very ill-defined in the altimetry, yet clearly are present as regional depressions include the Australe, Tranquillitatis, and Margims basins [3]. That both relatively deep and shallow basins exist on the Moon is not surprising; what is remarkable is that there is no correlation between basin depth and geologic age. Apparently, basin morphology is more dependent on local conditions (e.g., crustal thickness, lithospheric conditions at the time of impact) than age. Another unusual expression of topography for a basin is that of the degraded Lomonosov-Fleming basin [3,6]. This feature appears as a quasi-circular, smooth plateau of nearly constant elevation about 500 km across. Such an expression is likely caused by infilling of the basin with ancient mare basalts, covered by highland plains and reexposed as the ejecta of dark halo impact craters [7,8]. This interpretation is supported by the mafic signature of the plains in this region in the Clementine global color image [9] and the presense of elevated amounts of iron in the highland crust here [10]. The altimetry data also show many depressions that are likely to be previously unrecognized basins. For example, depressions near the crater Darwin (20 degrees S, 70 degrees W; basin about 300 km diameter), eastern Mare Frigoris (55 degrees N, 30 degrees W; basin about 700 km across), and east of Mare Humboldtianum (60 degrees N, 130 degrees E; basin about 400 km diameter) are probably degraded impact basins. To date, over 45 basins and their rings have been mapped on the Moon and the relief and volumes of the basins have been measured. Work continues on the analysis of this numerical data, which should give insight into the processes of basin formation and planetary evolution. References: [1] Wilhelms D. E. (1987) USGS Prof. Pap. 1348, 302 pp. [2] Spudis P. D. (1993) Geology of Multi-Ring Impact Basins, Cambridge Univ., 263 pp. [3] Nozette S. et al. (1994) Science, 266, 1835. [4] Zuber M. T. et al. (1994) Science, 266, 1839. [5] Spudis P. D. et al. (1994) Science, 266, 1848. [6] Wilhelms D. and El-Baz F. (1977) USGS Map I-948. [7] Schultz P. H. and Spudis P. D. (1979) Proc. LPSC 10th, 2899. [8] Schultz P. H. and Spudis P. D. (1982) Nature, 302, 233. [9] Lucey P. G. et al. (1994) Science, 266, 1855. [10] Lucey P. G. et al. (1995) Science, 268, 1150.
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