A photogeoIogical reconnaissance ofViking mosaics and images ofthe Tharsisuddome has been carried out. Fifteen new areas of transcurrent faulting have been locatedudwhich, together with other struétures previously detected, support a modeI in which theudThaumasia PIateau, the southeastem part of the Tharsis dome, is proposed to be anudindependent lithospheric block that experienced buckling and thrust faulting in LateudN oachian or Early Hesperian times as a result of an E-W directed compression. Evidence isudpresented that this stress fieId, rather than the Tharsis uplift, was decisive in the inception ofudValles Marineris, which we consider a transtensive, dextral accident. The buckling spacingudpermits us, rnoreover, to tentatively reconstruct a Martian Hesperian lithosphere similar inudeIastic thickness to the mean present terrestrial oceanic lithosphere, thus sí.lpporting theudpossibility of a restricted lithospheric mobility in that periodo Tharsis lithosphere was againudsubjected to shear stresses in Amazonian times, a period in which important accidents,suchudas strike-slip faults, wrinkle ridges, and straight and sigmoidal graben, were formed under audthin-skin tectonic regime, while the lithosphere as a: mechanical unit had become too thickudand sttong to buckle. The possibIe causes of those stresses, and especially their relationshipsudto a putative period of pIate tectonics, are discussed.
展开▼
