Lobate Scarps

Tectonics: Lobate scarps are the most prominent tectonic features.

Characteristics:

• Distributed globally
• 100's kilometers long
• Up to several kilometers high
• Asymmetric cross-sections
  • steep sloping scarp face and gently sloping back scarp
• Rounded crests
• Sinuous but generally linear to arcurate planforms
• Offset crater floors and walls

Beagle Rupes (left) and Discovery Rupes (right) (Credit: NASA/John Hopkins University Applied Physics Laboritory/Carnegie Institute of Washington)

Lobate scarp discorvered by MESSENGER during its 2nd flyby (Credit: NASA/John Hopkins University Applied Physics Laboritory/Carnegie Institute of Washington)

What? Lobate scarps are interpreted to be the surface expression of major thrust faults (compressive features).

When? Scarp formation postdated the intercrater plains, possibly forming after the smooth plains, during the Tolstojan and Calorian Periods.

How? They are generally attributed to global contraction of the planet resulting from a cooling interior. Several kilometers of radial contraction have occurred. Contraction of the planet occurs from (1) thermal contraction of a cooling lithosphere, mantle, and core, and (2) a liquid-solid phase change. As the liquid iron core frezes a solid iron inner core, the more dense solid core has a smaller volume. The estimate of global contraction provides a constraint on models of the thermal evolution of Mercury's interior.

Core Solidification

solid core density >

liq. core density

Volume of liquid solidifying to become the inner core

Thermal Contraction

ΔV = αΔT