Bell Regio, Venus: Integration of remote sensing data and terrestrial analogs for geologic analysis

Abstract

The geology and surface morphology of Bell Regio (18'42"N, 32'58"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 behaviors predicted by theoretical models. Five major volcanic sources are identified from geologic mapping (Tepev Mons, Nefertiti corona, a large shield volcano east of Tepev, and two small edifices southeast of Tepev). The volcano Api Mons lies northeast of the main Bell uplift. The oldest volcanic units are associated with an extensive low shield volcano east of Tepev Mons and a small edifice southeast of Tepev. The annular flow apron of Tepev Mons formed next, with volcanism at a second small edifice on the southeast flank of Tepev Mons producing the youngest flow units. Comparisons between Magellan data, terrrestrial radar images, and field topography profiles suggest that only three units resemble terrestrial a'a flows; the remainder are consistent with smoother 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 circumferential 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 steep slopes (up to 40 degrees along the east flank), a relatively flat summit, and two large (11 and 31 km) calderas. Though covered in places by high-dielectric material, the Tepev Mons summit area is relatively 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 between individual altimeter footprints inside and outside the larger eastern 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 surrounding Nefertiti corona, and Potanina crater ejecta is the likely source material for radar-dark wind streaks south of Tepev Mons. A low-dielectric (?=2?3) triangular region on the south flank of Tepev Mons may be a pyroclastic or crater ejecta deposit which has been spread westward by the wind. This region has undergone a wide variety of volcanic processes, with a major shift in eruptive style from the older low-relief eastern volcanic center to the steep slopes and large summit calderas characteristic of Tepev Mons and the two smaller edifices.