Superposed ridges of the Hesperia planum area on Mars
TL;DR: The main factors effective in mare ridge formation have been (i) a large areal, or maybe even global, shortening and compression, (ii) major crustal tectonics, and (iii) the moderation of tectonic movements by the megaregolith discontinuity layer(s) between surface lavas and the bedrock leaving the compressional thrust to dominate over other fault movements.
Abstract: Mare ridges of the Hesperia Planum area form linear, reticular and circular structures. The main factors effective in mare ridge formation have been (i) a large areal, or maybe even global, shortening and compression, (ii) major crustal tectonics, and (iii) the moderation of tectonic movements by the megaregolith discontinuity layer(s) between surface lavas and the bedrock leaving the compressional thrust to dominate over other fault movements in surface tectonics.
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TL;DR: Contractional features on Mars were identified on the basis of photogeologic evidence of crustal shortening and comparison with terrestrial and planetary analogs as discussed by the authors, and three classes of structures, wrinkle ridges, lobate scarps and high-relief ridges were mapped and their spatial and temporal distribution assessed.
Abstract: Contractional features on Mars were identified on the basis of photogeologic evidence of crustal shortening and comparison with terrestrial and planetary analogs. Three classes of structures, wrinkle ridges, lobate scarps and high-relief ridges, were mapped and their spatial and temporal distribution assessed. Wrinkle ridges account for over 80% of the total cumulative length of the mapped contractional features and occur in smooth plains material interpreted to be volcanic in origin. Lobate scarps, not wrinkle ridges, are the dominant contractional feature in Martian highland material. The pattern of contractional features in the western hemisphere reflects the hemispheric-scale influence of the Tharsis rise. Although no comparable hemispheric-scale pattern is observed in the eastern hemisphere, prominent regional-scale patterns exist, the most notable of which occurs in Hesperia Planum. Contractional features that locally parallel the trend of the crustal dichotomy boundary in the eastern hemisphere suggest the influence of stresses related to the evolution of the dichotomy. Compressional deformation apparently peaked during the Early Hesperia, if the tectonic features are roughly the same age as the units in which they occur. This peak in compressional deformation corresponds with Early Hesperian volcanic resurfacing of a large portion of the planet. Thermal history models for Mars, based on an initially hot planet, are inconsistent with estimates of the timing of peak compressional tectonism and the rate of volcanism. A pulse of global volcanism during the Early Hesperian may have resulted in a punctuated episode of rapid cooling and global contraction that contributed to compressional tectonism. Although global contraction may have contributed a significant component of the total stress that resulted in compressional deformation on Mars, nonhydrostatic horizontal stresses derived from local and regional-scale sources are necessary to account for the uniform orientations of the tectonic features.
181 citations
TL;DR: Montesi et al. as discussed by the authors attributed ridge spacing to an instability of the lithosphere under horizontal compression, which results in periodically spaced faults, and linked the difference of ridge spacing in the northern lowlands and in the highland ridged plains to the difference in crustal thickness via the depth of the brittle-ductile transition (BDT).
Abstract: [1] 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 [Montesi 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].
115 citations
Cites background from "Superposed ridges of the Hesperia p..."
...Hesperia Planum displays two perpendicular sets of ridges as well (Figure 3c), but the ridges are so intertwined that they probably formed contemporaneously [Raitala, 1988; Mangold et al., 2000]....
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...ridges are so intertwined that they probably formed contemporaneously [Raitala, 1988; Mangold et al., 2000]....
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TL;DR: The interpretation of the geometry of blind thrusts on Mars appears to be quite varied and remains controversial, although some models suggest they may ultimately flatten into the brittle-ductile transition in the middle to lower crust.
Abstract: ▪ Abstract Wrinkle ridges accommodate very low amounts of shortening strain around immense volcanic constructs and within impact basins on Mars. They originate from stresses distributed uniformly throughout the brittle lithosphere and are consistently located in stratified deposits, including lava flows and sediment. Most recent models interpret wrinkle ridges as the surface manifestation of folding above underlying blind thrusts that accommodate similarly low strain and likely penetrate tens of kilometers into the brittle crust. Alternative models suggest shortening accommodated by some wrinkle ridges is confined to only the upper few kilometers of the crust. The interpretation of the geometry of blind thrusts on Mars appears to be quite varied and remains controversial, although some models suggest they may ultimately flatten into the brittle-ductile transition in the middle to lower crust. Small-scale crenulations superposed on ridges are interpreted as produced by high-level back thrusts nucleating at...
108 citations
TL;DR: In this article, the mechanism responsible for the periodic spacing of wrinkle ridges observed on the Tharsis Plateau of Mars is investigated by examining the characteristics of the spacing of ridges in six major provinces on the plateau; these regions were further divided into domains on the basis of ridge orientation.
Abstract: The mechanism responsible for the periodic spacing of wrinkle ridges observed on the Tharsis Plateau of Mars is investigated by examining the characteristics of the spacing of ridges in six major provinces on the plateau; these regions were further divided into domains on the basis of ridge orientation. The ridges are interpreted to be folds resulting from buckling, followed by reverse to thrust faulting (flexure-fracture). Several buckling models that may account for the periodic nature of the ridges are analyzed. The model that would account for the periodic spacing and the asymmetric fold geometry of the ridges involves plastic yielding confined to the hinge area, that would result in rapid closing of the fold and, with continued horizontal shortening, the eventual development of reverse to thrust faulting.
103 citations
01 Jun 1975
TL;DR: An evaluation of existing theories on the existence of the planet's metallic core is presented in this paper, where topics considered are: (1) magnetic fields; (2) surface geology; (3) cosmochemical models.
Abstract: An evaluation of existing theories on the existence of the planet's metallic core is presented. Topics considered are: (1) magnetic fields; (2) surface geology; (3) cosmochemical models.
101 citations
References
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TL;DR: In this article, the geometrical consequences of displacements along strike-slip faults with respect to the associated deformation, terminal and otherwise, are discussed in detail, based on model experiments and by field examples.
365 citations
TL;DR: In this article, it was shown that the majority of smooth plains on Mercury were produced by volcanism which occurred at the close of the period of late heavy bombardment similar to that on the moon and Mars.
Abstract: Mercury appears to have a tectonic framework and diastrophic history not found on other terrestrial planets explored to date (earth, Mars, and the moon). On the part of the planet viewed by Mariner 10, only two localized areas show evidence of tensional stresses, both of which are apparently associated with the Caloris basin. Lobate scarps occur in the remainder of the explored region and appear to be primarily reverse or thrust faults which have resulted from compressive stresses acting on a global scale. The period of compression represented by these scarps occurred during the final phase of heavy bombardment on Mercury and was probably caused by crustal shortening due to a small decrease in the planet's radius. Stratigraphic, volumetric, and albedo considerations together with distribution indicate that the majority of smooth plains on Mercury were produced by volcanism which occurred at the close of the period of late heavy bombardment similar to that on the moon and Mars. Several generations of plains are evident; the oldest may have resulted in part from an early differentiation of the planet.
325 citations
TL;DR: In this article, the authors developed a hypothesis that the spatial and temporal distributions of linear rilles and mare ridges in the mare regions of the moon are the products of two superposed stress systems: a local stress due to lithospheric loading by basalt fill in mare basin, and a global thermal stress associated with the thermal history of the lunar interior.
Abstract: A hypothesis is developed that the spatial and temporal distributions of linear rilles and mare ridges in the mare regions of the moon are the products of two superposed stress systems: a local stress due to lithospheric loading by basalt fill in the mare basin, and a global thermal stress due to the thermal history of the lunar interior. Quantitative models for stress in the Serenitatis basin area, including the global thermal stress associated with lunar thermal history, are presented and used to account for the spatial distribution, the orientations, and the formation times of rilles and ridges in that region. The models provide a simple explanation for the localization of the most recent eruption sites of mare basalt magmas to mare basin edges.
217 citations
TL;DR: In this paper, the authors describe some terrestrial features of similar morphology and scale that have formed under compressional stress systems similar to planetary wrinkle ridges (linear, asymmetric topographic highs) are common physiographic features on the Moon, Mars, and Mercury.
Abstract: Wrinkle ridges (linear, asymmetric topographic highs) are common physiographic features on the Moon, Mars, and Mercury. We describe here some terrestrial features of similar morphology and scale that have formed under compressional stress systems similar to planetary wrinkle ridges. All of the terrestrial analogs are produced by the anticlinal folding of rocks above reverse faults that shallow and typically break the surface. Characteristics common to both terrestrial and planetary ridges include (1) a linear, asymmetric antiformal shape; (2) tension cracks and grabens along the hinges of the antiform; (3) overlapping, en echelon lobes; (4) reversals of the sense of asymmetry along strike; (5) occurrence in compressional environments; and (6) similarity to features produced during compression of various materials in laboratory scale models. These similarities strongly suggest that planetary wrinkle ridges result from deformation associated with shallow thrust faults that either break or come close to the surface. Kinematic models capable of explaining the development of wrinkle ridges include (1) anticlinal folding of rocks over a buried thrust fault that may subsequently propagate to the surface and (2) fault-bend folding of upper-plate rocks over the surface-flattening bend of a thrust fault.
184 citations