Tessera (Venus): Difference between revisions
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===Pulsating Continents=== |
===Pulsating Continents=== |
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Differentiated, low density crust survives early global subduction events forming continental region. This region undergoes compression due to heating from the surrounding mantle. |
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==Variety of Tessera Terrain== |
==Variety of Tessera Terrain== |
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Revision as of 04:27, 28 February 2015
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]
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. [6] 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. [7] [8]
Formation
Tesserae represent an ancient time of globally thin lithosphere on Venus. [9] It was thought by many researches that the Tesserae might form a global "onion skin" of sorts, and extended beneath Venus's regional plains. [10] [11] However, the currently accepted models support regional formation.[12][7] These terrains formed due to various compressional, extensional, and shear forces that reflect unique interactions of the mantle with regional stresses. [7] [9]
Downwelling
Mantle downwelling, possibly due to mantle convection, causes compression and thickening of the crust, creating the compressional elements of tessera terrain. Isostatic rebound occurs due to the crustal thickening, creating a crustal plateau. After downwelling ends, a delamination event within the mantle produces extensional elements of tessera.
Lava Pond via Giant Impact
Melt due to a bolide impact on a thin lithosphere rises to the surface to form a lava pond. Convection throughout the lava pond resulted in surface deformation that created tessera terrain. Isostatic rebound of the solidified pond creates a crustal plateau structure.
Pulsating Continents
Differentiated, low density crust survives early global subduction events forming continental region. This region undergoes compression due to heating from the surrounding mantle.
Variety of Tessera Terrain
Individual patterns of Tessera Terrain record the variations in interactions of the mantle with local regional stresses. [7] [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. [13]
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. [13]
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. [13]
Basin and Dome Terrain consists of curved ridges and trough that form a pattern analogous to an egg carton.[13] 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. [13]
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. [13]
References
- ^ 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) - ^ 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) - ^ 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) - ^ 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) - ^ 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) - ^ 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) - ^ 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) - ^ 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) - ^ 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) - ^ Solomon, S.C. (1993). "The geophysics of Venus". Physics Today. 46: 38–55.
{{cite journal}}:|access-date=requires|url=(help) - ^ Turcotte, D.L. (1993). "An episodic hypothesis for Venusian tectonics". Journal of Geophysical Research. 98: 17061–17068.
{{cite journal}}:|access-date=requires|url=(help) - ^ 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) - ^ 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)