Mercurian TectonicsTectonics definedIt happened long, long agoPowerPoint PresentationThe Despinning ModelTectonics of a despun planetMercurian GridShortfalls of despinning aloneSimultaneous processesFault distributionSlide 11Surface featuresSuch an impact!Basin boundariesAntipodal effectsSlide 16Additional processesKalidasa - Milton Area (U1 - U2)Phidias Area (K)ReferencesMercurian TectonicsVirginia PasekTectonics definedAlso 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 MoonIt happened long, long agoChange in the shape of the lithosphereChange in radiusCaloris related eventsOnly on EarthFound on MercuryThe Despinning ModelTectonics of a despun planetLineaments found at N 50°, N 130° and weaker N - S trendsSimilar to MoonN 60°, N 120°2500 images studiedDifference between theoretical and observed gridsMercurian GridPattern of fractures, or weak zones, in the lithosphereMost ancient of all tectonic evidenceOccurred before any recognizable geological featuresSimilar to the MoonShortfalls of despinning aloneLobate scarps are just as abundant in the polar regions as the equatorialThe polar regions do not contain normal, or tension, faultsLobate scarps have pseudorandom orientationsThe lineament system is post-dated by some relatively young featuresSimultaneous processesSecular cooling and despinningFault distributionSurface featuresAncient tectonic grid, called “Mercurian Grid”Lobate and arcuate scarpsSuch 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 MercuryBorealis basin, located near the north pole is 1560 kmBasin boundariesAntipodal effectsCovers at least 336,000 km2Hills, depressions, and valleys that disrupt pre-existing landforms5-10 km wide and up to 2 km in heightSmooth terrain within some craters indicate that volcanic activity occurred after Caloris impactEffects enhanced due to Mercury’s large iron coreAntipodal effectsAdditional processesReactivated tectonic trends due to large impactLocal processesKalidasa - Milton areaThe Phildias areaTolstoj - Zeami areaKalidasa - Milton Area (U1 - U2)ThomasTwo troughs which can not be explained as coalescent secondary impactsPhidias 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.ReferencesR.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