LITHOSPHERIC-SCALE BUCKLING AND THRUST STRUCTURES ON MARS - THE COPRATES RISE AND SOUTH THARSIS RIDGE BELT

Detailed photogeologic mapping documents for the first time the deform ation sequence of the Coprates rise. Materials of Middle Noachian thro ugh perhaps Early Hesperian age were involved in the horizontal shorte ning of crustal and lithospheric rocks that produced uplift and asymme tric, east-vergent folding of these layers during the Late Noachian an d perhaps Early Hesperian. Previous suggestions of normal faulting as the deforming mechanism are not supported by the new mapping or by dis location models of rise topography. The most likely mechanism for prod ucing the Coprates rise is folding due to buckling instability and per haps thrust faulting. An extensive ridge belt concentric to south Thar sis is defined by a newly recognized system of approximately coeval lo ng-wavelength topographic ridges and swales that include the Coprates rise. Horizontal shortening of crust and lithosphere is manifested by periodically spaced structures at two different scales: wrinkle ridges spaced tens of kilometers apart and the south Tharsis system of ridge s spaced hundreds of kilometers apart. Both types of structures may be associated with early volcanotectonic activity and crustal thickening in south Tharsis. These and other large ridges indicate that lithosph eric buckling and thrust faulting may have been common on early Mars.