BELL REGIO, VENUS - INTEGRATION OF REMOTE-SENSING DATA AND TERRESTRIAL ANALOGS FOR GEOLOGIC ANALYSIS

The geology and surface morphology of Bell Regio (18-42-degrees-N, 32- 58-degrees-E) are investigated using a combination of Magellan, Venera , and analogous terrestrial data. The properties of surface units are compared to either direct terrestrial analog measurements or to the be haviors predicted by theoretical models. Five major volcanic sources a re identified from geologic mapping (Tepev Mons, Nefertiti corona, a l arge shield volcano east of Tepev, and two small edifices southest of Tepev). The volcano Api Mons lies northeast of the main Bell uplift. T he oldest volcanic units are associated with an extensive low shield v olcano east of Tepev Mons and a small edifice southeast of Tepev. The annular flow apron of Tepev Mons formed next, with volcanism at a seco nd small edifice on the southeast flank of Tepev Mons producing the yo ungest flow units. Comparisons between Magellan data, terrestrial rada r images, and field topography profiles suggest that only three units resemble terrestrial a'a flows; the remainder are consistent with smoo ther pahoehoe-type surfaces. This suggests that most of the flow units were erupted at relatively low volume effusion rates (<100 m3/s) over long periods of time or had very low viscosities. One flow unit has a knobby texture which resembles large tumuli or ridge structures. Much of the tectonic deformation in the area is in the form of fractures c ircumferential to the edifices and isolated blocks of tessera terrain; there are no rift zones such as those which occur at Beta Regio, Atla Regio, or Western Eistla Regio. Tepev Mons is characterized by very s teep slopes (up to 40-degrees along the east flank), a relatively flat summit, and two large (11 and 31 km) calderas. Though covered in plac es by high-dielectric material, the Tepev Mons summit area is relative ly smooth with the exception of annular rough deposits which ring the two calderas. These calderas are quite shallow (on the order of a few hundred meters at most), with no discernible difference in radius betw een individual altimeter footprints inside and outside the larger east ern feature. Magellan and Venera data suggest that the eastern caldera is covered by a layer of unconsolidated material. Ejecta from Miriam crater has produced a halo with a dielectric constant of 6-7 surroundi ng Nefertiti corona, and Potanina crater ejecta is the likely source m aterial for radar-dark wind streaks south of Tepev Mons. A low-dielect ric (epsilon=2-3) triangular region on the south flank of Tepev Mons m ay be a pyroclastic or crater ejecta deposit which has been spread wes tward by the wind. This region has undergone a wide variety of volcani c processes, with a major shift in eruptive style from the older low-r elief eastern volcanic center to the steep slopes and large summit cal deras characteristic of Tepev Mons and the two smaller edifices.