Post on 15-Jan-2016
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Mercurian Tectonics
Virginia Pasek
Tectonics definedAlso known as crustal deformation
tectonics is the result of stresses in the outer layers of a planet that are produced by thermal and/or mechanical processes
Occurs on terrestrial planets and the Moon
It happened long, long agoChange in the shape of the lithosphereChange in radiusCaloris related events
Only on Earth
Found on Mercury
The Despinning Model
Tectonics of a despun planetLineaments found at N
50°, N 130° and weaker N - S trends
Similar to MoonN 60°, N 120°
2500 images studiedDifference between
theoretical and observed grids
Mercurian GridPattern of fractures, or weak zones, in the
lithosphereMost ancient of all tectonic evidenceOccurred before any recognizable
geological featuresSimilar to the Moon
Shortfalls of despinning aloneLobate scarps are just as abundant in the
polar regions as the equatorialThe polar regions do not contain normal,
or tension, faultsLobate scarps have pseudorandom
orientationsThe lineament system is post-dated by
some relatively young features
Simultaneous processesSecular cooling and despinning
Fault distribution
Surface featuresAncient tectonic grid, called “Mercurian Grid”
Lobate and arcuate scarps
Such an impact!Review
Mercury’s diameter is 4878 km
Caloris basin is 1550 kilometers in diameter 32% of the size of
Mercury
Approximately 336,000 km2 on antipodal side affected by impact
Caloris is not the largest impact on MercuryBorealis basin,
located near the north pole is 1560 km
Basin boundaries
Antipodal effectsCovers at least 336,000 km2
Hills, depressions, and valleys that disrupt pre-existing landforms
5-10 km wide and up to 2 km in heightSmooth terrain within some craters
indicate that volcanic activity occurred after Caloris impact
Effects enhanced due to Mercury’s large iron core
Antipodal effects
Additional processesReactivated tectonic trends due to large
impactLocal processes
Kalidasa - Milton areaThe Phildias areaTolstoj - Zeami area
Kalidasa - Milton Area (U1 - U2)
Thomas
Two troughs which can not be explained as coalescent secondary impacts
Phidias Area (K)Absence of
secondaries, central peak, and wall terraces
Thomas proposes that Phidias depression is due to a tectonic subsidence of a nearly circular area.
ReferencesR.G. Strom, A.L. Sprague, Exploring
Mercury: The Iron Planet (Springer, New York, 2003)
P.G. Thomas, Planet. Space Sci. 45, pp. 3-13 (1997)
J.W. Head et al., Space Sci. Rev. 131, pp. 41-84 (2007)