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At least 199 records · Page 11Linked to original sources
USGS1980

Geologic map of the Argyre quadrangle of Mars

The geology of the Argyre quadrangle of Mars is dominated by the conspicuous Argyre basin, defined by a rim of rugged mountain blocks that surround a nearly circular expanse of plains 800 km across. Of the large (greater than 500 km in diameter) basins identified on Mars, Argyre is the best preserved and possibly youngest. Basins appear to be traps for eolian debris and evidently are source areas for some of the dust storms that periodically envelop the planet. The quadrangle lies within the densely cratered province that characterizes the southern hemisphere, contrasting with sparsely cratered plains generally confined to the northern hemisphere. Northwest of Argyre an outlier of sparsely cratered, ridged plains extends into the quadrangle from the Coprates region. Northeast of the basin are the cratered uplands, parts of which are presumed to represent remnants of the earliest martian crust (Wilhelms, 1974). South of the quadrangle the cratered plateau is replaced by the pitted, etched, layered, and mantled terrains that characterize the south polar region (Sharp, 1973a; Condit and Soderblom, 1978). Constructional volcanic landforms were not recognized within the map area.

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USGS1980

Geologic map of the Sinus Sabaeus quadrangle of the Mars

The area included in the Sinus Sabaeus quadrangle represents an ancient cratered surface that has been modified by a combination of impact cratering, fluvial, eolian, and, probably, volcanic processes. Impact cratering has been the dominant process. Cumulative frequencies of craters larger than 20 km for the entire quadrangle (fig. 4) are only about a factor of two below the idealized lunar steady-s ta te curve (Moor e , 1964; Trask, 1966). Two of the units mapped (hilly, channeled , and cratered material a n d hilly and cratered material) have cumulative frequencies of craters larger than 40 km that are near the same as the idealized steady-state curve. The young map units (smooth plains material and units of the crater Bakhuysen ) have cumul ative frequencies of craters a distributions that are similar in form and magnitude to the average frequency distributions of lunar maria. Ages of surfaces recorded by craters larger than 5 km (fig. 4) are probably measured in several billions of years. Direct comparison with lunar cra t ers would place the age of the young units (smooth plains material and units of Bakhuysen ) i n the range 3.2 to 3.5 billion years, but procedures for making such a comparison are controversial. (See, for example, Soderblom and others, 1974 ; Neukum and Wise, 1976). These units may be either a few tenths of a billion years older or about a billion years younger than the average lunar maria. The more cratered units (hilly, channel e d, and cratered material and hill y and cratered material) may represent the cumulative result of about 4 billion years of cratering (Soderblom and others, 1974 ; Neukem and Wise, 1976).

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