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Mercurian Tectonics. Virginia Pasek. Tectonics 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 Moon. It happened long, long ago.

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Mercurian Tectonics

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Mercurian tectonics l.jpg

Mercurian Tectonics

Virginia Pasek


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Tectonics 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 Moon


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It happened long, long ago

  • Change in the shape of the lithosphere

  • Change in radius

  • Caloris related events


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Found on Mercury

Only on Earth


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The Despinning Model


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Tectonics 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 grids


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Mercurian 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 Moon


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Shortfalls 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 features


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Simultaneous processes

Secular cooling and despinning


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Fault distribution


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Surface features

  • Ancient tectonic grid, called “Mercurian Grid”

  • Lobate and arcuate scarps


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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 km

Such an impact!


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Basin boundaries


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Antipodal 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 core


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Antipodal effects


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Additional processes

  • Reactivated tectonic trends due to large impact

  • Local processes

    • Kalidasa - Milton area

    • The Phildias area

    • Tolstoj - Zeami area


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Kalidasa - Milton Area (U1 - U2)

  • Two troughs which can not be explained as coalescent secondary impacts

Thomas


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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.


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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 (2007)


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