Styles of tectonic deformations on Venus: Analysis of Venera 15 and 16 data

Abstract

Analysis of the radar images obtained by Veneras 15 and 16 leads to the conclusion that the ridge‐and‐groove structures on the surface of Venus are the result of tectonic deformation. Although the mechanism of such deformation cannot yet be unequivocally deduced, several styles of deformation can be described. Areal deformation occurs where horizontal stresses have operated over large areas. Shear deformation appears in bands showing differential longitudinal deformation. Transversal stresses operating over long and relatively narrow areas have produced belt deformation. Circular deformation is related to a specific locus of the stresses. The absence of densely cratered areas indicates that the terrains were deformed after the period of heavy bombardment. The origin of the stresses could be drag of the lithosphere by asthenospheric currents or gravity‐induced spreading of surface material over upwellings. A general conclusion is that in the surveyed area of Venus neither terrestrial plate tectonics nor lunar‐highland‐type terrain exists.

Corona Associations and Their Implications for Venus

“…Tessera or complex ridge terrain (CRT, Bindschadler and Head, 1991) was defined as a terrain previously used to relate coronae and extensional belts type characterized by a completely deformed surface of elsewhere on Venus (Baer et al, 1994). ridges and troughs, intersecting at various angles, typically At latitude 9"S, longitude 248.5" flows of corona unit a lying at higher elevations than surrounding materials, and from the central asymmetric corona are overlain by flows likely resulting from extensive horizontal deformation from Javine Corona at latitude SOS, longitude 251°, mapped (Basilevsky et al, 1986;Bindschadler and Head, 1989, as corona unit b (unit cb). Javine Corona is heart-shaped, 1991).…”

Surface evolution of Venus

“…The Venera 15/16 SAR image resolution was sufficient to directly observe many key elements of Venus geology [Barsukov et al, 1986;Basilevsky et al, 1986]. Dominance of volcanic plains was confirmed, as was the presence of indisputable large volcanic constructs.…”

“…In the western part of Ishtar Terra, in close association with tessera terrain, are seen Mountain belts, which surround the volcanic plateau Lakshmi [e.g., Barsukov et al, 1986;Basilevsky et al, 1986;Crumpler et al, 1986;Pronin, 1992;Solomon et al, 1992]. They consist of clusters of parallel (within the given belt) ridges (see Figure 2).…”

Image resolution and evaluation of genetic hypotheses for planetary landscapes

“…Venhigh width-to-depth ratio and remarkably constant era 15/16 SAR images, with 1 to 2 km ground resolution, failed to detect many such channels on the northern quarter of the planet (Barsukov et al, 1985;Basilevsky et al, 1986). The current high temperatures and pressures at the surface of Venus do not allow for the stability of liquid water, although some theories suggest that water may have been stable early in the history of Venus (Kasting and Toon, 1989).…”