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Tessera (Venus)

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Tesserae are a form of heavily deformed terrain on Venus, characterized by two or more intersecting tectonic elements, high topography, and subsequent high radar back-scatter.[1] Tesserae often represent the oldest material at any given location and are among the most tectonically deformed terrains on Venus's surface. [2] [3]

Overview

Tesserae were first noticed by the Pioneer Venus Orbiter, as regions of anomalous radar properties indicating high topography. This was later investigated by the Venera 15 and Venera 16 orbiters. Through SAR imaging, it was discovered that these high topography regions with abnormally high backscatter represented intensely deformed terrain[1], dubbed tesserae, (Greek for "Tile") due to its variety of patterns. [4] Tessera Terrain does not participate in the global resurfacing events of Venus. [5]

Formation

Tesserae represent an ancient time of globally thin lithosphere on Venus. [6] It was thought by many researches that the Tesserae might form a global "onion skin" of sorts, and extended beneath Venus's regional plains. [7] [8] However, Tesserae did not form globally, and instead formed regionally at distinct times.[9][10] These terrains formed due to various compressional, extensional, and shear forces that accompany mantle up-welling beneath thin crust. Each area of Tessera Terain reflects a unique interaction of a deep-mantle plume and regional stresses. [10] [6]

Variety of Tessera Terrain

Individual patterns of Tessera Terrain record the variations in interactions of mantle plumes with local regional stresses. [10] [1]This variation manifests itself in a wide array of diverse terrain types. Mutiple types of sampled Tessera Terrain are below, however, they are not meant as a classification scheme, and instead emphasize the variety of terrain types. [11]

Fold Terrain is easily recognizable by its well defined linear fabrics. This type of terrain is composed of long ridges and valleys, greater than 100km long, that are cross cut by minor extensional fractures that run perpendicular to the fold axes of the ridges. This likely formed due to unidirectional contraction. [11]

Lava Flow Terrain is named such due to its resemblance to Pahoehoe flows found on Earth, with long curving ridges. It is thought that this terrain may be formed due to displacement and deformation due to movement of the material beneath these crustal pieces.

Ribbon Terrain

S-C Terrain is named such due to its geometric similarity to S-C tectonic fabrics on Earth. It consists of two main structures: synchronous folds and small, 5 to 20km long graben that cross cut the folds perpendicularly. Unlike many other types of tessera terrain, S-C terrain indicates a simple, rather than complex deformation history in which deformation due to widespread motion on Venus is widely distributed. This type of terrain also indicates that strike-slip movement on Venus's surface is possible. [11]

Basin and Dome Terrain consists of curved ridges and trough that form a pattern analogous to an egg carton.[11] These structures represent multiple phases of deformation, and are considered the most complex appearing style of tessera.[1] Basin and dome terrain is typically found within the center of crustal plateaus. [11]

Star Terrain is composed of multiple graben and fractures that trend in many directions, but radiate in a star-like pattern. This pattern is thought to be due to doming underneath previously deformed and fractured areas, in which the local uplift causes the radiating pattern. [11]

Locations

Tesserae are recognized as covering 7.3% of Venus's surface, approximately 33.2×106 km, and occur mostly within a few extensive provinces. [12] They are heavily concentrated between 0°E and 150°E. These longitudes represent a large area between a crustal extension center in the Aphrodite Terra and a crustal convergence center in Ishtar Terra. [1] Tesserae are exposed almost entirely within Venus's crustal plateaus. [10] [13]

Interpretive outline of tessera terrain (white outline) imposed on "GIS Map of Venus" (GIS Map of Venus source: USGS Astrogeology Science Center)

References

  1. ^ a b c d e Bindschadler, Duane; Head, James (1991). "Tessera Terrain, Venus: Characterization and Models for Origin and Evolution". Journal of Geophysical Research. 96 (B4): 5889–5907. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)
  2. ^ Ivers, Carol; McGill, George. "Kinematics of a Tessera Block in the Vellamo Planitia Quadrangle". Lunar and Planetary Science. 29. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)
  3. ^ Hansen, Vicki; Willis, James (1998). "Ribbon Terrain Formation, Southwestern Fortuna Tessera, Venus: Implications for Lithosphere Evolution". Icarus. 132: 321–343. {{cite journal}}: |access-date= requires |url= (help)
  4. ^ Head, James (1990). "Venus Trough and Ridge Tessera: Anolog to Earth Oceanic Crust Formed at Spreading Centers?". Journal of Geophysical Research. 95 (B5): 7119–7132. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)
  5. ^ Romeo, I.; Turcotte, D.I. (2008). "Pulsating continents on Venus: An explanation for crustal plateaus and tessera terrains". Earth and Planetary Science Letters. 276: 85–97. {{cite journal}}: |access-date= requires |url= (help)
  6. ^ a b Hansen, Vicki; Phillips, Roger; Willis, James; Ghent, Rebecca (2000). "Structures in tessera terrain, Venus: Issues and answers". Journal of Geophysical Research. 105 (E2): 4135–4152. {{cite journal}}: |access-date= requires |url= (help)
  7. ^ Solomon, S.C. (1993). "The geophysics of Venus". Physics Today. 46: 38–55. {{cite journal}}: |access-date= requires |url= (help)
  8. ^ Turcotte, D.L. (1993). "An episodic hypothesis for Venusian tectonics". Journal of Geophysical Research. 98: 17061–17068. {{cite journal}}: |access-date= requires |url= (help)
  9. ^ Hansen, V.L.; Lopez, I. (2009). "Implications of Venus Evolution Based on Ribbon Tessera Relation Within Five Large Regional Areas". Lunar and Planetary Science Conference. {{cite journal}}: |access-date= requires |url= (help)
  10. ^ a b c d Hansen, Vicki; Banks, Brian; Ghent, Rebecca (1999). "Tessera terrain and crustal plateaus, Venus". Geology. 27 (12): 1071–1074. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)
  11. ^ a b c d e f Hansen, Vicki; Willis, James (1996). "Structural Analysis of a Sampling of Tesserae: Implications for Venus Geodynamics". Icarus. 123: 296–312. {{cite journal}}: |access-date= requires |url= (help)
  12. ^ Ivanov, Mikhail; Head, James (2011). "Global Geologic Map of Venus". Planetary and Space Science. 59: 1559–1600. doi:10.1016/j.pss.2011.07.008. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help)
  13. ^ Campbell, Bruce; Campbell, Donald; Morgan, Gareth; Carter, Lynn; Nolan, Micael (2015). "Evidence for crater ejecta on Venus tessera terrain from Earth-based radar images". Icarus. 250: 123–130. {{cite journal}}: |access-date= requires |url= (help)
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