Research Article| August 01, 2004 Global geologic context for rock types and surface alteration on Mars Michael B. Wyatt; Michael B. Wyatt 1Department of Geological Sciences, Arizona State University, Tempe, Arizona 85251, USA Search for other works by this author on: GSW Google Scholar Harry Y. McSween, Jr.; Harry Y. McSween, Jr. 2Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee 37996, USA Search for other works by this author on: GSW Google Scholar Kenneth L. Tanaka; Kenneth L. Tanaka 3U.S. Geological Survey, Flagstaff, Arizona 86001, USA Search for other works by this author on: GSW Google Scholar James W. Head, III James W. Head, III 4Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA Search for other works by this author on: GSW Google Scholar Geology (2004) 32 (8): 645–648. https://doi.org/10.1130/G20527.1 Article history received: 02 Feb 2004 rev-recd: 09 Apr 2004 accepted: 16 Apr 2004 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Michael B. Wyatt, Harry Y. McSween, Kenneth L. Tanaka, James W. Head; Global geologic context for rock types and surface alteration on Mars. Geology 2004;; 32 (8): 645–648. doi: https://doi.org/10.1130/G20527.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Petrologic interpretations of thermal emission spectra from Mars orbiting spacecraft indicate the widespread occurrence of surfaces having basaltic and either andesitic or partly altered basalt compositions. Global concentration of ice-rich mantle deposits and near-surface ice at middle to high latitudes and their spatial correlation with andesitic or partly altered basalt materials favor the alteration hypothesis. We propose the formation of these units through limited chemical weathering from basalt interactions with icy mantles deposited during periods of high obliquity. Alteration of sediments in the northern lowlands depocenter may have been enhanced by temporary standing bodies of water and ice. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
A rift zone over 6000 km in total length runs along the border of Lada Terra, a highland in the southern hemisphere of Venus, and Lavinia Planitia, a basin that has been interpreted as a site of early‐stage mantle downwelling. Along the length of the rift are a number of volcanic centers of widely varying morphology and volcanic output. These include coronae, radially fractured domes, and large flow fields similar in scale to terrestrial flood basalts. We develop a model for the origin of extension related to passive rifting in response to stresses created by the adjacent downwelling. Volcanism and extension at other rifts on Venus, such as Devana Chasma, have been attributed to deep‐seated mantle plume activity. In contrast, we interpret the origin of extension and volcanism along the Lada rift to be linked to upwelling and decompression melting of mantle material due to rifting and, possibly, to counterflow associated with downwelling. Extension occurred generally prior to the formation of volcanic centers and the eruption of large‐scale flow fields, although most of the volcanic centers have been fractured by continued extension along the rift. Current debate over the formation of terrestrial flood basalts centers on the necessity of preexisting extension and stretched and thinned lithosphere to produce enhanced decompression melting within a large plume head or mantle thermal anomaly. Our studies of large‐scale flow fields associated with the Lada rift and coronae on Venus indicate that extension is a prerequisite for the formation of the majority of large‐scale flow units on Venus.
The background lineated plains on Europa are locally highly modified and destroyed in regions known as chaos and lenticulae. Produced there are (1) isolated fragments and polygons of background material which rotate and translate, (2) matrix, which fills in the areas between the fragments and polygons, and (3) surface discolorations. Using observations and constraints from high‐resolution Galileo images, we find that a model for the formation of these terrains which involves mobilization and migration of brines, and a possible percolation phase transition as the Europan lithosphere is warmed, can readily explain the vast majority of their characteristics. In addition, the presence of melt fractions of a few percent in the adjacent ice framework may enhance the creep rate and the accompanying deformation rates. The characteristics and distribution of lenticulae suggest that among the strong candidates for heat sources for brine migration and ice mobilization processes is diapirism linked to solid‐state convection in a layer underlying a brittle lid and possibly overlying a liquid water layer.
[1] The acquisition of new global elevation data from the Lunar Orbiter Laser Altimeter, carried on the Lunar Reconnaissance Orbiter, permits quantification of the surface roughness properties of the Moon at unprecedented scales and resolution. We map lunar surface roughness using a range of parameters: median absolute slope, both directional (along-track) and bidirectional (in two dimensions); median differential slope; and Hurst exponent, over baselines ranging from ∼17 m to ∼2.7 km. We find that the lunar highlands and the mare plains show vastly different roughness properties, with subtler variations within mare and highlands. Most of the surface exhibits fractal-like behavior, with a single or two different Hurst exponents over the given baseline range; when a transition exists, it typically occurs near the 1 km baseline, indicating a significant characteristic spatial scale for competing surface processes. The Hurst exponent is high within the lunar highlands, with a median value of 0.95, and lower in the maria (with a median value of 0.76). The median differential slope is a powerful tool for discriminating between roughness units and is useful in characterizing, among other things, the ejecta surrounding large basins, particularly Orientale, as well as the ray systems surrounding young, Copernican-age craters. In addition, it allows a quantitative exploration on mare surfaces of the evolution of surface roughness with age.
We report on ages derived from impact crater counts for exposed mare basalt units in the northern part of the lunar nearside hemisphere (Mare Frigoris), the eastern and northeastern part of the nearside hemisphere (Lacus Temporis, Joliot, Hubble, Goddard, Mare Marginis, and Mare Smythii), the central part of the nearside hemisphere (Palus Putredinis, Mare Vaporum, and Sinus Medii), and the southwestern part of the nearside hemisphere (Grimaldi, Crüger, Rocca A, Lacus Aestatis, and Schickard). In Mare Frigoris, we dated 37 basalt units, showing ages from 2.61 to 3.77 Gyr, with most units being formed in the late Imbrian period between 3.4 and 3.8 Gyr ago. In Mare Vaporum we dated six spectrally homogeneous units that show model ages of 3.10 to 3.61 Gyr. Our model ages of basalts in Mare Marginis range from 3.38 to 3.88 Gyr and are mostly older than basalts in Mare Smythii (3.14–3.48 Gyr). The model ages of four units in Sinus Medii indicate that the basalts in this region formed 3.63 to 3.79 Gyr ago. We find an excellent agreement of our crater size‐frequency model ages of the Palus Putredinis area, which contains the Apollo 15 landing site, with the radiometric ages of Apollo 15 samples. According to our crater counts, basalts in Palus Putredinis are 3.34 Gyr old and this compares favorably with the radiometric ages of 3.30–3.35 Gyr of the olivine‐normative and quartz‐normative basalts of the Apollo 15 landing site. Lacus Aestatis is a small irregular‐shaped mare patch in the southwestern nearside and shows an Imbrian age of 3.50 Gyr; basalts in Lacus Temporis in the northeastern nearside formed between 3.62 and 3.74 Gyr ago and are, therefore, older than the basalts in Lacus Aestatis. We found that basalts in craters of the southwestern nearside (Schickard, Grimaldi, Crüger, and Rocca A) are also mostly younger than basalts in craters of the northeastern nearside (Hubble, Joliot, and Goddard). While basalt ages vary between 3.16 and 3.75 Gyr in the southwest, basalts in the northeast are 3.60–3.79 Gyr old. These results confirm and extend the general distribution of ages of mare basalt volcanism and further underline the predominance of older mare basalt ages in the eastern and southern nearside and in patches of mare peripheral to the larger maria, in contrast to the younger basalt ages on the western nearside (Oceanus Procellarum).
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