Columbus crater in the Terra Sirenum region of the Martian southern highlands contains light‐toned layered deposits with interbedded sulfate and phyllosilicate minerals, a rare occurrence on Mars. ...Here we investigate in detail the morphology, thermophysical properties, mineralogy, and stratigraphy of these deposits; explore their regional context; and interpret the crater's aqueous history. Hydrated mineral‐bearing deposits occupy a discrete ring around the walls of Columbus crater and are also exposed beneath younger materials, possibly lava flows, on its floor. Widespread minerals identified in the crater include gypsum, polyhydrated and monohydrated Mg/Fe‐sulfates, and kaolinite; localized deposits consistent with montmorillonite, Fe/Mg‐phyllosilicates, jarosite, alunite, and crystalline ferric oxide or hydroxide are also detected. Thermal emission spectra suggest abundances of these minerals in the tens of percent range. Other craters in northwest Terra Sirenum also contain layered deposits and Al/Fe/Mg‐phyllosilicates, but sulfates have so far been found only in Columbus and Cross craters. The region's intercrater plains contain scattered exposures of Al‐phyllosilicates and one isolated mound with opaline silica, in addition to more common Fe/Mg‐phyllosilicates with chlorides. A Late Noachian age is estimated for the aqueous deposits in Columbus, coinciding with a period of inferred groundwater upwelling and evaporation, which (according to model results reported here) could have formed evaporites in Columbus and other craters in Terra Sirenum. Hypotheses for the origin of these deposits include groundwater cementation of crater‐filling sediments and/or direct precipitation from subaerial springs or in a deep (∼900 m) paleolake. Especially under the deep lake scenario, which we prefer, chemical gradients in Columbus crater may have created a habitable environment at this location on early Mars.
The Crust of the Moon as Seen by GRAIL Wieczorek, Mark A.; Neumann, Gregory A.; Nimmo, Francis ...
Science,
02/2013, Letnik:
339, Številka:
6120
Journal Article
Recenzirano
Odprti dostop
High-resolution gravity data obtained from the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft show that the bulk density of the Moon's highlands crust is 2550 kilograms per cubic ...meter, substantially lower than generally assumed. When combined with remote sensing and sample data, this density implies an average crustal porosity of 12% to depths of at least a few kilometers. Lateral variations in crustal porosity correlate with the largest impact basins, whereas lateral variations in crustal density correlate with crustal composition. The low-bulk crustal density allows construction of a global crustal thickness model that satisfies the Apollo seismic constraints, and with an average crustal thickness between 34 and 43 kilometers, the bulk refractory element composition of the Moon is not required to be enriched with respect to that of Earth.
We present detailed stratigraphic and spectral analyses that focus on a region in northern Sinus Meridiani located between 1°N to 5°N latitude and 3°W to 1°E longitude. Several stratigraphically ...distinct units are defined and mapped using morphologic expression, spectral properties, and superposition relationships. Previously unreported exposures of hydrated sulfates and Fe/Mg smectites are identified using MRO CRISM and MEX OMEGA near‐infrared (1.0 to 2.5 μm) spectral reflectance observations. Layered deposits with monohydrated and polyhydrated sulfate spectral signatures that occur in association with a northeast‐southwest trending valley are reexamined using high‐resolution CRISM, HiRISE, and CTX images. Layers that are spectrally dominated by monohydrated and polyhydrated sulfates are intercalated. The observed compositional layering implies that multiple wetting events, brine recharge, or fluctuations in evaporation rate occurred. We infer that these hydrated sulfate‐bearing layers were unconformably deposited following the extensive erosion of preexisting layered sedimentary rocks and may postdate the formation of the sulfate‐ and hematite‐bearing unit analyzed by the MER Opportunity rover. Therefore, at least two episodes of deposition separated by an unconformity occurred. Fe/Mg phyllosilicates are detected in units that predate the sulfate‐ and hematite‐bearing unit. The presence of Fe/Mg smectite in older units indicates that the relatively low pH formation conditions inferred for the younger sulfate‐ and hematite‐bearing unit are not representative of the aqueous geochemical environment that prevailed during the formation and alteration of earlier materials. Sedimentary deposits indicative of a complex aqueous history that evolved over time are preserved in Sinus Meridiani, Mars.
Data from the Gravity Recovery and Interior Laboratory (GRAIL) mission have revealed that ∼98% of the power of the gravity signal of the Moon at high spherical harmonic degrees correlates with the ...topography. The remaining 2% of the signal, which cannot be explained by topography, contains information about density variations within the crust. These high-degree Bouguer gravity anomalies are likely caused by small-scale (10′s of km) shallow density variations. Here we use gravity inversions to model the small-scale three-dimensional variations in the density of the lunar crust. Inversion results from three non-descript areas yield shallow density variations in the range of 100–200kg/m3. Three end-member scenarios of variations in porosity, intrusions into the crust, and variations in bulk crustal composition were tested as possible sources of the density variations. We find that the density anomalies can be caused entirely by changes in porosity. Characteristics of density anomalies in the South Pole-Aitken basin also support porosity as a primary source of these variations. Mafic intrusions into the crust could explain many, but not all of the anomalies. Additionally, variations in crustal composition revealed by spectral data could only explain a small fraction of the density anomalies. Nevertheless, all three sources of density variations likely contribute. Collectively, results from this study of GRAIL gravity data, combined with other studies of remote sensing data and lunar samples, show that the lunar crust exhibits variations in density by ± 10% over scales ranging fromcentimeters to100′s of kilometers.
Orbital topographic, image, and spectral data show that sulfate‐ and hematite‐bearing plains deposits similar to those explored by the MER rover Opportunity unconformably overlie the northeastern ...portion of the 160 km in diameter Miyamoto crater. Crater floor materials exhumed to the west of the contact exhibit CRISM and OMEGA NIR spectral signatures consistent with the presence of Fe/Mg‐rich smectite phyllosilicates. Based on superposition relationships, the phyllosilicate‐bearing deposits formed either in‐situ or were deposited on the floor of Miyamoto crater prior to the formation of the sulfate‐rich plains unit. These findings support the hypothesis that neutral pH aqueous conditions transitioned to a ground‐water driven acid sulfate system in the Sinus Meridiani region. The presence of both phyllosilicate and sulfate‐ and hematite‐bearing deposits within Miyamoto crater make it an attractive site for exploration by future rover missions.
The tectonic record of Mars is dominated by compressional wrinkle ridges on volcanic surfaces, and these structures have been widely used as a record of tectonic and geodynamic evolution. This study ...analyzes the density of compressional tectonic structures and inferred strain as functions of time, using the lengths and heights of compressional ridges together with geologic estimates of surface age. Our analyses confirm an apparent peak in compressional strain in the late Noachian and early Hesperian, and comparatively lower values before and after. The lower tectonic strain in the early and middle Noachian relative to the early Hesperian reflects the incompleteness of the ancient compressional tectonic record of strain, as older surfaces should accumulate more strain than younger surfaces. This strain deficit necessitates other means of accommodating contractional strain in the ancient crust, including distributed strain and small-scale faulting. The abrupt decrease in the accumulated tectonic strain and strain rate after the early Hesperian reflects a rapid episode of global contraction followed by much lower rates, in conflict with models of steady-state mantle evolution. The decreasing strain rate may be explained by a changing mantle rheology due to volcanic outgassing. Alternatively, the strain history may be explained by the dominance of mantle plumes in the late Noachian and early Hesperian associated with the formation of Tharsis and the early Hesperian volcanic provinces, which could have led to a pulse of rapid contraction caused by disequilibrium cooling and volcanic outpourings. The tectonic record of strain on Mars – including the incomplete ancient record and evidence for strong departures from steady-state models – may have implications for the interpretation of the tectonic record and thermal evolution of other bodies as well.
•The history of compressional tectonic strain on Mars was evaluated.•Compressional strain peaks strongly in the early Hesperian.•A strain deficit in ancient surfaces indicates non-tectonic accommodation of strain.•Strain decreased abruptly after the early Hesperian.•Thermal evolution has not been steady state, and may be dominated by plumes.
The moon before mare Broquet, A.; Andrews-Hanna, J.C.
Icarus (New York, N.Y. 1962),
01/2024, Letnik:
408
Journal Article
Recenzirano
The crust of the Moon experienced a unique geodynamic evolution, beginning with its crystallization from a magma ocean, continuing through a period of heavy impact bombardment, and followed by ...extensive basaltic mare volcanism. All these events have left crucial records imprinted in the form of topographic features and gravity anomalies. Here, we invert gravity and topography data using a two-layer thin-shell loading model under the premise of pre-mare isostasy to investigate the global structure of the crust and solve for feldspathic crust and mare thickness, together with mare-induced flexure. The tectonic record and partially buried crater population are used to constrain the bulk of mare volcanism to have been emplaced on a 40 km elastic lithosphere, although mare within large impact basins may have formed on a thinner elastic lithosphere. The mare thickness and associated flexure are removed to calculate a map of the surface and crust of the Moon before mare volcanism. The pre-mare surface in the Oceanus Procellarum region is found to be ∼2 km lower than the surrounding nearside, and several possible explanations, including a giant impact, pore space annealing, isostatic adjustment, and crustal erosion induced by a mantle plume or thermal anomaly, are discussed. The pre-mare elevation map further sheds light on the ring structure of Imbrium, which is seen to resemble that of Orientale. Imbrium's outermost ring is observed to be at a larger radial distance to the northeast relative to the south, indicating that some level of lithospheric variability affected ring formation at the time of impact. The western part of Imbrium's ring within Oceanus Procellarum is not found in the pre-mare topography, implying that it either never formed or that some processes erased its signature from gravity and topography. The feldspathic, pre-mare, crust is found to be ∼7 km thinner within large nearside basins than in models not accounting for the high-density mare. The pre-fill floor of these basins was ∼6 km deeper than currently observed, and together with their updated crustal structure, these new insights have implications for impact simulations that try to reproduce the crustal structure of nearside mare basins.
•Mare thickness inverted from gravity and topography assuming pre-mare isostasy.•Maria within large basins are 8 km on average, higher than outside, 1.6 km.•PKT was affected by pore space annealing, isostatic adjustment, or crustal erosion.•Imbrium's western ring never formed or was erased from gravity and topography.•An updated crustal structure for the large mare mascon basins is presented.
A volcanic inventory of the Moon Broquet, A.; Andrews-Hanna, J.C.
Icarus (New York, N.Y. 1962),
03/2024, Letnik:
411
Journal Article
Recenzirano
The volcanic and magmatic activity of the Moon is intimately tied to its internal thermal and geodynamic evolution through time. While the extrusive nearside maria dominate the volcanic record, ...little is known regarding their underlying structure and the details of their emplacement. Intrusive activity is even more enigmatic, with most intrusions expressing little to no surface signature. Although prior studies have provided insights into the local igneous activity, no global compilation has been conducted. Here, we present a volumetric inventory of extrusive and intrusive activity. Gravity and topography data are inverted using a two-layer loading model to constrain mare and cryptomare thickness. The mean thickness of mare units is found to be 2.8 km, though with substantial lateral variations, with average values of 7.9 km within large mare basins compared to 1.6 km outside of these basins. This substantial variation in mare thickness associated with minimal change in the surface topography may be explained by some combination of long-distance transport of low viscosity mare and/or a buoyancy control limiting mare eruptions to a constant level surface. Our preferred volumes of mare and cryptomare are 18.2×106 km3 and 2.2×106 km3, respectively. Crustal intrusions associated with linear gravity anomalies, floor-fractured craters, ring dikes, graben, and beneath volcanic constructs, are investigated and yield a total volume of 9.1×106 km3. Our inventory reveals that intrusive activity dominates in the farside (intrusive:extrusive ratio of 5:2), whereas extrusive volcanism is more pronounced in the nearside (1:5). The combined volume of intrusives and extrusives is found to be 3 times greater in the nearside than in the farside. Both are related to the lunar asymmetry in which the thinner crust and warmer subsurface beneath the Procellarum KREEP terrane enables enhanced melting and magma ascent. These observations may have implications for the interpretation of the thermal and geodynamic history of other celestial bodies, where intrusive volcanism remains poorly constrained.
•Inverted volume of mare and cryptomare are 18×106 km3 and 2×106 km3, respectively.•Mare distribution implies a buoyancy control on eruption and long-distance flows.•Intrusion below large gravity anomalies, FFCs, graben, and plutons sum to 9×106 km3.•Volume of igneous materials is 3 times greater in the nearside than in the farside.•Intrusive:extrusive ratios are 1:5 and 5:2 for the near and farside, respectively.
Hesperian Mars was characterized by a unique style of geodynamic activity that left crucial volcano-tectonic records in the form of extensive flood lavas covered by wrinkle ridges. Yet, little is ...known about the context of their formation. Here, we perform a tectonic and geophysical investigation of Hesperia Planum, a 1700-km-diameter volcanic plain covered by wrinkle ridges. Our tectonic analysis reveals that the planum has the highest density of wrinkle ridges on the planet and a characteristic compressional peak strain of about 3.20 × 10−3, almost 2 times larger than typical Hesperian compressional strains. We invert gravity and topography data and find that simple crustal loading and volcanism cannot explain the tectonic record. An additional source of deformation is thus required. We demonstrate that a loading sequence of plume-induced uplift, volcanism, and subsidence, following an evolutionary path similar to flood basalt provinces on Earth better fits the observations. This plume model is able to explain the peak strain, crustal thinning, and low relief of Hesperia Planum. The inferred plume head size (∼1400 km) and temperature anomaly (∼320 K) are consistent with large terrestrial plumes. Based on a fit to the tectonic record, we determine a plume center location that correlates with a cluster of wrinkle ridges, local crustal thinning, and a circular magnetic low, where the latter could be the result of a thermal demagnetization of the lithosphere in the presence of the ascending plume. Our analysis suggests that scattered mantle plumes could be at the origin of Hesperia Planum and other late Noachian to early Hesperian volcanic provinces within the highlands.
•Hesperia Planum shows volcanism, compression, crustal demagnetization and thinning•Compressional tectonics cannot be explained by global cooling or volcanic loading•The planum is inferred to have formed as a terrestrial plume-induced flood basalt•The formation sequence involves plume-induced uplift, volcanism, and subsidence•Hesperian plumes likely formed ridged volcanic plains outside of the Tharsis province.
The Arabia Terra region, an area of ∼1 × 107 km2 lying south of the hemispheric dichotomy boundary and centered at (25E, 5N), is a unique physiographic province with topography and crustal thickness ...intermediate between those of the southern highlands and northern lowlands. Previous workers have identified numerous morphological indicators suggestive of erosion. Using altimetry data returned by the Mars Orbiter Laser Altimeter (MOLA) on the Mars Global Surveyor (MGS) along with gravity data from the Mars Reconnaissance Orbiter (MRO), we place geophysical constraints on the amount of erosion permitted within Arabia Terra. Admittance estimates using a multitaper, spatiospectral localization approach provide a best fit to the observations through degree 50 at an elastic lithosphere thickness of 15 km. The elevation difference between Arabia Terra and the highlands would require as much as 5 km of erosion in certain areas to yield the current topography, neglecting the effects of subsequent flexure. However, incorporating flexural rebound requires substantially more erosion, up to 25 km, in order to reproduce the elevation and crustal thickness deficit of Arabia Terra. Such a large amount of erosion would result in exterior flexural uplift surpassing 1 km and gravity anomalies exceeding observations by ∼60 mGal. Consequently, it is unlikely that Arabia Terra was formed from surface erosion alone. We determine that no more than 3 × 107 km3 of material could have been removed from Arabia Terra, while 1.7 × 108 km3 of erosion is required to explain the observed crustal thickness.
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