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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. E6, 5048, doi:10.1029/2002JE001974, 2003

Clues to the lithospheric structure of Mars from wrinkle ridge sets and localization instability

Laurent G. J. Montési

Massachusetts Institute of Technology, Cambridge, Massachusetts, USA


Maria T. Zuber

Massachusetts Institute of Technology, Cambridge, Massachusetts, USA


Abstract

Wrinkle ridges are a manifestation of horizontal shortening in planetary lithospheres, for which deformation is localized on faults that underlie individual ridges. In ridged plains of Mars, such as Solis Planum or Lunae Planum, wrinkle ridges are spaced ∼40 km apart, whereas in the Martian northern lowlands, where ridges are identified only in Mars Observed Laser Altimeter (MOLA) altimetric data, the ridge spacing is at least ∼80 km. We attribute ridge spacing to an instability of the lithosphere under horizontal compression. The localization instability, which results in periodically spaced faults [ Montési and Zuber, 2003a ], links the difference of ridge spacing in the northern lowlands and in the highland ridged plains to the difference of crustal thickness via the depth of the brittle-ductile transition (BDT). In Solis and Lunae Plana, where the crust is 50 to 60 km thick, the crust may be ductile at depth, limiting faulting to the BDT of crustal rocks. In the lowlands, the crust is only about 30 km thick and may be brittle throughout. Thus the depth of faulting may be controlled by the BDT of mantle rocks, which is roughly a factor of two deeper than that of crustal rocks. The geotherm can be identical in both regions, at 12 ± 3 K.km−1, although differences of a few K.km−1 can be accommodated within this model. The heat flux implied by this geotherm is similar to the heat produced by radiogenic decay 3 Gyr ago. Our analysis provides a rheological explanation for the difference in spacing between ridges in the highlands and the lowlands, in contrast to the suggestion of Head et al. [2002] , who proposed that alternating lowlands ridges are buried by sediments. In addition, finite element models that use the lithospheric structure deduced from ridge spacing show that modest gradients of crustal thickness or heat flux across a ridged plains favor the formation of faults dipping toward high-elevation areas, as may be the case in Solis Planum [ Golombek et al., 2001 ].

Received 3 September 2002; accepted 12 March 2003; published 5 June 2003.

Index Terms: 5475 Planetology: Solid Surface Planets: Tectonics (8149); 5455 Planetology: Solid Surface Planets: Origin and evolution; 5418 Planetology: Solid Surface Planets: Heat flow; 8120 Tectonophysics: Dynamics of lithosphere and mantle—general; 3210 Mathematical Geophysics: Modeling.

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Citation: Montési, L. G. J., and M. T. Zuber (2003), Clues to the lithospheric structure of Mars from wrinkle ridge sets and localization instability, J. Geophys. Res., 108(E6), 5048, doi:10.1029/2002JE001974.