ALBERT

Description: 〈span〉〈div〉Abstract〈/div〉Graben, defined as landforms produced by normal faulting, have long been recognized on the Moon, but their map patterns, as well as topographic expressions, have not been studied systematically. The topography across graben and its along-strike variations reveal details about the growth of the normal faults forming the graben. Individual normal faults grow in length by the propagation of fault tips during slip events, which can also enlarge the displacement along the fault plane. Displacement and length accumulate and grow larger over time with more slip events, fault interaction, and linkage. We measured fault lengths and vertical offsets and then calculated the displacement for lunar graben using data from the camera and laser altimeter onboard the 〈span〉Lunar Reconnaissance Orbiter〈/span〉. Our study systematically investigated 14 graben systems across the lunar surface. Graben lengths were found to range from ∼43 to 453 km, and displacements ranged from ∼127 to 1115 m. These displacements were plotted against graben fault length to produce slip distributions, which revealed growth patterns involving mechanical interaction and fault linkage. Displacement-to-length scaling was used to further study the evolution of graben-bounding normal faults. We observed a sublinear growth pattern for lunar graben-bounding normal faults, consistent with growth of faults via segment linkage, where different stages of linkage are present on the lunar surface. Lunar graben-bounding faults show higher scaling ratios than previously estimated, likely due to variations in host-rock properties and mechanical stratigraphy.〈/span〉

Description: Dense coverage of high-resolution topographic measurements from the Lunar Orbiter Laser Altimeter (LOLA) now allows for a global survey of the long-wavelength morphology of lunar grabens, with important implications for the geologic processes that form them. Comparing model ground displacements for grabens that arise solely from faulting, and from faulting involving a dike at depth, with topographic measurements across some of the most prominent and best-preserved grabens shows that many of them are underlain by a dike. Matching ground displacement models to topographic observations is the only way to detect, and also provide specific geometric information about, dikes too small to be resolved in available gravity and magnetic measurements, and thus allows for quantitative assessments of magma source depths and required magma overpressures. Dike-forming magmas are likely mantle derived, originating from depths greater than 20 km, with dike widths exceeding 100–500 m. Such dike geometric properties are only plausible if a mechanically weak lunar lithosphere was under extension at the time of dike emplacement.

Description: The Rembrandt basin is the largest well-preserved impact feature in the southern hemisphere of Mercury. Its smooth volcanic infill hosts wrinkle ridges and graben, and the entire basin is cross-cut by the Enterprise Rupes scarp system. On the basis of the Model Production Function crater chronology, our analysis shows that the formation of the Rembrandt basin occurred at 3.8±0.1 Ga during the Late Heavy Bombardment, consistent with previous studies. We also find that the smooth plains interior to the basin were emplaced between 3.7 and 3.6±0.1 Ga, indicative of a resurfacing event within the Rembrandt basin that is consistent with the presence of partially buried craters. These youngest plains appear temporally unrelated to basin formation, and so we regard their origin as likely to be due to volcanism. We identify the same chronological relationship for the terrain cross-cut by Enterprise Rupes to the west of the basin. Therefore, volcanic activity affected both the basin and its surroundings, but ended prior to the majority of basin- and regional-scale tectonic deformation. If Enterprise Rupes formed prior to the Rembrandt basin, then regional-scale tectonic activity along this structure might have lasted at least 200 myr.

Description: 〈span〉Graben, defined as landforms produced by normal faulting, have long been recognized on the Moon, but their map patterns, as well as topographic expressions, have not been studied systematically. The topography across graben and its along-strike variations reveal details about the growth of the normal faults forming the graben. Individual normal faults grow in length by the propagation of fault tips during slip events, which can also enlarge the displacement along the fault plane. Displacement and length accumulate and grow larger over time with more slip events, fault interaction, and linkage. We measured fault lengths and vertical offsets and then calculated the displacement for lunar graben using data from the camera and laser altimeter onboard the 〈span〉Lunar Reconnaissance Orbiter〈/span〉. Our study systematically investigated 14 graben systems across the lunar surface. Graben lengths were found to range from ∼43 to 453 km, and displacements ranged from ∼127 to 1115 m. These displacements were plotted against graben fault length to produce slip distributions, which revealed growth patterns involving mechanical interaction and fault linkage. Displacement-to-length scaling was used to further study the evolution of graben-bounding normal faults. We observed a sublinear growth pattern for lunar graben-bounding normal faults, consistent with growth of faults via segment linkage, where different stages of linkage are present on the lunar surface. Lunar graben-bounding faults show higher scaling ratios than previously estimated, likely due to variations in host-rock properties and mechanical stratigraphy.〈/span〉

Description: Orbital images of Mercury obtained by the MESSENGER spacecraft have revealed families of troughs, interpreted to be graben, on volcanic plains material that largely or completely buried preexisting craters and basins. The graben are partially to fully encircled by rings of contractional wrinkle ridges localized over the rims of the buried impact features to form systems of associated contractional and extensional landforms. Most of the buried craters and basins with graben identified to date are located in the extensive volcanic plains that cover much of Mercury’s northern high latitudes. The distinctive relationship between wrinkle ridges and graben in buried craters and basins on Mercury is interpreted to be the result of a combination of extensional stresses from cooling and thermal contraction of thick lava flow units and compressional stresses from cooling and contraction of the planet’s interior.

Description: 〈span〉Although Earth is the only known planet on which plate tectonics operates, many small- and large-scale tectonic landforms indicate that deformational processes also occur on the other rocky planets. Although the mechanisms of deformation differ on Mercury, Venus, and Mars, the surface manifestations of their tectonics are frequently very similar to those found on Earth. Furthermore, tectonic processes invoked to explain deformation on Earth before the recognition of horizontal mobility of tectonic plates remain relevant for the other rocky planets. These connections highlight the importance of drawing analogies between the rocky planets for characterizing deformation of their lithospheres and for describing, applying appropriate nomenclature, and understanding the formation of their resulting tectonic structures. Here we characterize and compare the lithospheres of the rocky planets, describe structures of interest and where we study them, provide examples of how historic views on geology are applicable to planetary tectonics, and then apply these concepts to Mercury, Venus, and Mars.〈/span〉