The largest tesserae occur on the surface of major plateau-shaped highlands of Venus ( Fig. Tesserae cover ~ 8% of the surface of Venus the size of individual tessera occurrences varies from a few hundred kilometers up to several thousand kilometers. Tesserae are defined as radar-bright, topographically elevated, equidimensional or elongated areas that are complexly deformed by at least two sets of coupled contractional (ridges) and extensional (grooves) tectonic structures. 4) is among the most deformed regions on Venus. The surrounding plains embay practically all tessera massifs, meaning that the tessera is the oldest recognizable unit on Venus. The elevated regions where the major rift zones are associated with coronae and large volcanoes represent another type of territory where tessera terrain is rare or absent. Tessera terrain is concentrated in the equatorial zone and at high northern latitudes there is a distinct paucity of tessera terrain south of about 30° S ( Figure 5), where the vast low-lying plains dominate the surface of Venus. The smaller tesserae are within the midlands and only a few small fragments of a tessera occur on the floor of large lowland basins. The largest tesserae occur on the surface of major plateau-shaped highlands of Venus ( Figure 1B). Tesserae cover ∼8% of the surface of Venus the size of individual tessera occurrences varies from a few hundred kilometres up to several thousand kilometres. Understanding of the basic structural characteristics of trough and ridge terrain is more tentative, and models involving a spreading process or convergence and relaxation merit further study.The tessera terrain ( Figure 4) is among the most deformed regions on Venus. We find that horizontal convergence and late stage gravitational relaxation are the most consistent with basic observations for subparallel ridged terrain and disrupted terrain. Modificational models, in which deformation occurs as a response to the presence of elevated regions, consist of (1) gravity sliding and (2) gravitational relaxation. Formational models, in which high topography is created along with surface deformation, include (1) horizontal convergence, (2) mantle upwelling, (3) crustal underplating, and (4) a seafloor spreading analogy. Observed characteristics of tessera terrain are compared to predictions of models in order to begin to address the question of its origin and evolution.
Three types of tessera terrain can be defined on the basis of structural patterns: subparallel ridged terrain (T sr), trough and ridge terrain (T tr) and disrupted terrain (T ds). Available Pioneer Venus line of sight gravity data suggest that tessera terrain is compensated at shallow depths relative to many topographic highs on Venus and may be supported by crustal thickness variations.
Tesserae are characterized by regionally high topography, a high degree of small scale surface roughness, and sets of intersecting tectonic features. Tessera terrain is the dominant tectonic landform in the northern high latitudes of Venus mapped by the Venera 15 and 16 orbiters and is concentrated in the region between the mountain ranges of western Ishtar Terra and Aphrodite Terra.
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