The geology and geomorphology of the Venus surface as revealed by the radar images obtained by Veneras 15 and 16

Abstract

A region‐by‐region condensed description of almost all of the area that was radar‐photographed by Veneras 15 and 16 is presented. Using some generalizations, the diversity of terrain was reduced to a discrete set from which a geological‐morphological map was constructed. The predominant type of terrain of the studied area is a plain that was tentatively subdivided into five morphological types: ridge‐and‐band, patchy rolling plain, dome‐and‐butte plain, smooth plain, and high smooth plain. Stratigraphically, the ridge‐and‐band plains are the oldest and the smooth plains are the youngest. The stratigraphic position of the other types is yet to be determined. Large sections of the plains show similarities to the mare‐type basaltic plains of the moon, Mercury, and Mars. Other types of terrain are combinations of ridges and grooves in various patterns: linear parallel, orthogonal, diagonal or chevron‐like, and chaotic. In some places the ridge‐and‐groove terrain is Stratigraphically below the plain material, but in other places it appears to be plain material that has been subsequently deformed. Near the eastern and western boundaries of Ishtar Terra large (several hundred kilometers in diameter) ring‐like features can be seen that are named coronae or ovoids. Evidence of tectonic deformation and the presence of flow‐like patterns support their designation as volcano‐tectonic features. Beta Regio seems to be an uplifted plain showing evidence of rifting and volcanism. All types of terrain are sparesely peppered with craters of obvious impact morphology. Their average density gives the plain an age range of 0.5 to 1×109 years. The fact that many impact craters are still in the pristine state indicates a very low rate of surface reworking, at least for the last 0.5 to 1×109 years. No evidence for water‐erosion‐sedimentation processes has been found. The tectonic activity of Venus has no equivalent on the moon, Mercury, or even Mars, and can be compared only with that of the Earth. Intensive horizontal deformation, previously known only on Earth, occurs on Venus, but in a characteristic Venusian style.

Geologic units on Venus: evidence for their global correlation

“…The name Fortuna was derived from Fortuna Tessera, which is a large tessera massif containing several di erent varieties of this terrain, and is also the place where this type of the terrain was ®rst identi®ed in the analysis of the Venera 15/16 SAR images (Barsukov et al, 1986). The complex of tessera-forming deformation forms a discontinuity separating Fortuna Group materials from the materials of younger groups.…”

“…It is radar bright and has crosscutting sets of ridges and grooves of evident tectonic nature. First identi®ed on images taken by the Venera 15/16 spacecraft with a resolution of 1± 2 km, tessera showed ridge and groove spacing of about 5±20 km (Barsukov et al, 1986;Sukhanov, 1992). Higher resolution (120±220 m) Magellan images show that these ridges and grooves are typically fractured with a spacing of about 1 km and down to the limit of image resolution.…”

Background heatflow on hotspot planets: Io and Venus

“…This corresponds to Pe ~ 0.03 and .$ 10% enhancement of the background heat flow. On the basis of crater counts [Barsukov et al, 1986;Grimm and Solomon, 1987], this recurrence interval is about the smallest conceivable. However, it must be stressed that intrusive activity can come close to achieving much of the same effect (in terms of heatflow) as surface lava flows, yet have a less direct impact on geomorphology, so the situation is not fully determined from the radar data.…”

Mapping and modeling of radial fracture patterns on Venus

“…The most common association (33.5%) is with coronae, which are large circular volcano-tectonic structures characterized by annuli of extensional faults or compressional ridges and often with a peripheral moat [Barsukov et al, 1986;Stofan et al, 1992]. Volcanic edifices are associated with 27.7% of the radial systems; if the category of younger proto-edifices is considered together with developed edifices, this includes 43% of the population.…”