HR: 0800h
AN: P41A-0891    [Abstracts]
TI: History of Major Degradational Events in the Ancient Highlands of Mars: Preliminary Results From Crater Depth and Diameter Measurements
AU: Boyce, J M
EM: jboyce@higp.hawaii.edu
AF: Hawaii Institute of Geophysics and Planetology, University of Hawaii, Manoa, Honolulu, HI 96822 United States
AU: * Mouginis-Mark, P
EM: pmm@higp.hawaii.edu
AF: Hawaii Institute of Geophysics and Planetology, University of Hawaii, Manoa, Honolulu, HI 96822 United States
AU: Garbeil, H
EM: harold@higp.hawaii.edu
AF: Hawaii Institute of Geophysics and Planetology, University of Hawaii, Manoa, Honolulu, HI 96822 United States
AU: Soderblom, L A
EM: lsoderblom@usgs.gov
AF: U.S. Geological Survey, 2255 N. Gemini Dr, Flagstaff, AZ 86004 United States
AB: Impact crater depths (d) and diameter (D) were measured for 1398 craters in the diameter range 6 km to over 100 km using the 128th degree MOLA DEM in 10 test locations (Meridiani, Margaritifer, Memnonia, Ma'adin, Promethei, Thyles, S. Argyre, Sirenum, Tempe, and Dueteronilus Regions) in an effort to gain insight into the degradational history of the ancient highlands of Mars. The d/D scatter plots commonly show that Early/Middle Noachian-age terrains located in the mid-latitude (i.e., $\sim$40§S and 40§N) include 3 modes formed by clusters of point that approximately parallel the fresh crater curve, but are displaced relative to each other and have slightly different d/D slopes. The slopes decrease with increased age of the mode. The oldest mode is Early Noachian-age and, most likely, is the result of craters buried by ancient ridged plains materials. The intermediate (in age, relative crater depth, and slope of the d/D distribution) mode is Middle Noachian and is most likely associated with the formation of the valley networks common to these regions. Craters in the third mode are younger than late Noachian in age and include the deepest craters (some have fresh crater d/D), and have the steepest d/D distribution suggesting crater modification by such degradation processes as eolian infilling. In contrast, similar age highland terrains in the high latitudes of Mars (i.e., 40§S to 70§S and 40§N to 55§N) show two modes in their d/D distributions. These are similar to the two oldest modes with the shallowest craters in the mid-latitude regions and, remarkably, indicate that these regions include no craters with fresh d/D values. This suggests either the operation of a process only in the high latitudes of Mars that recently significantly degraded or buried all craters or that the crust of the region is composed of materials that cause craters to initially form relatively shallow and that the recognized fresh crater curve does not apply in these regions.
DE: 5415 Erosion and weathering
DE: 5420 Impact phenomena (includes cratering)
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting