Isostatic Compensation of the Lunar Highlands

Isostatic Compensation of the Lunar Highlands The lunar highlands are isostatically compensated at large horizontal scales, but the specific compensation mechanism has been difficult to identify. With topographic data from the Lunar Orbiter Laser Altimeter and gravity data from the Gravity Recovery and Interior Laboratory, we investigate support of highland topography. Poor correlation between crustal density and elevation shows that Pratt compensation is not important in the highlands. Using spectrally weighted admittance, we compared observed values of geoid‐to‐topography ratio (GTR) with those predicted by isostatic models. Observed GTRs are 25.8+7.5–5.7 m/km for the nearside highlands and 39.3+5.7–6.2 m/km for the farside highlands. These values are not consistent with flexural compensation of long‐wavelength topography or Airy isostasy defined under an assumption of equal mass in crustal columns. Instead, the observed GTR values are consistent with models of Airy compensation in which isostasy is defined under a requirement of equal pressures at equipotential surfaces at depth. The gravity and topography data thus reveal that long‐wavelength topography on the Moon is most likely compensated by variations in crustal thickness, implying that highland topography formed early in lunar history before the development of a thick elastic lithosphere. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Geophysical Research: Planets Wiley

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Publisher
Wiley Subscription Services, Inc., A Wiley Company
Copyright
©2018. American Geophysical Union. All Rights Reserved.
ISSN
2169-9097
eISSN
2169-9100
D.O.I.
10.1002/2017JE005362
Publisher site
See Article on Publisher Site

Abstract

The lunar highlands are isostatically compensated at large horizontal scales, but the specific compensation mechanism has been difficult to identify. With topographic data from the Lunar Orbiter Laser Altimeter and gravity data from the Gravity Recovery and Interior Laboratory, we investigate support of highland topography. Poor correlation between crustal density and elevation shows that Pratt compensation is not important in the highlands. Using spectrally weighted admittance, we compared observed values of geoid‐to‐topography ratio (GTR) with those predicted by isostatic models. Observed GTRs are 25.8+7.5–5.7 m/km for the nearside highlands and 39.3+5.7–6.2 m/km for the farside highlands. These values are not consistent with flexural compensation of long‐wavelength topography or Airy isostasy defined under an assumption of equal mass in crustal columns. Instead, the observed GTR values are consistent with models of Airy compensation in which isostasy is defined under a requirement of equal pressures at equipotential surfaces at depth. The gravity and topography data thus reveal that long‐wavelength topography on the Moon is most likely compensated by variations in crustal thickness, implying that highland topography formed early in lunar history before the development of a thick elastic lithosphere.

Journal

Journal of Geophysical Research: PlanetsWiley

Published: Jan 1, 2018

Keywords: ; ; ; ; ;

References

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