Search

Surface unloading due to impact cratering results in lava filling the crater floor. Elevation differences in the crater floor, a common geological phenomenon on the Moon, represent direct evidence of cratering processes. However, few studies have been conducted on mare-filled craters on the Moon. Al-Biruni (81 km) is a farside impact crater with an inclined topographic profile on its floor. We quantitatively measure the morphology of Al-Biruni and model the basaltic lava emplacement to depict the cratering process. Differential subsidence due to melt cooling, wall collapse, impact conditions and structural failure were assessed as potential factors influencing the formation of the elevation differences on the floor. The results suggest that pre-impact topography is a plausible cause of the differences in floor elevation within Al-Biruni. Other factors may also play a role in this process, affecting lava flow by altering the topography of the crater floor after the impact. Thus, regardless of whether the lava inside the crater is impact-generated or comes from outside the crater, altering topography at different stages of the cratering process is an essential factor in creating the sloped terrain on the crater floor. [ABSTRACT FROM AUTHOR]

Rocks produced by diverse processes, from condensation in space to impacts on planetary surfaces to volcanism, contain both crystals and amorphous material. Crystallinity provides information on the thermal history of the sample and is especially important in characterizing volcanic rocks and pyroclasts because lava rheology is profoundly influenced by the crystal content. Crystallinity is typically quantified via microscopy, using transmitted light or backscattered electrons. However, many samples present visibly ambiguous textures such as intimate intergrowth of crystal phases, and/or crystal sizes extending down to the nanometer scale. Here, we apply calorimetric methods involving heat capacity and enthalpy to assess the crystallinity of a series of volcanic samples. We tested three different approaches, using differential scanning calorimetry, on 30–40 mg aliquots of powdered basalts from the 2018 Kīlauea lower East Rift Zone. The first approach involves determining the magnitude of the increase in heat capacity at the glass transition, which can determine crystallinity to a 1σ precision of ±3%. The second approach is based on the enthalpy of fusion, which requires a longer more complex procedure with results that are typically more uncertain than for the heat capacity method, with a 1σ of ±6%. A final method utilizing differences in enthalpies calculated from the heat capacities required the most complex procedure and has the greatest uncertainty of ±18%. Preliminary results for lavas with microscopically determined crystallinities ranging from 11 to 98% indicate that crystallinity based on calorimetric data can be tens of percent higher than the average value identified using microscopy and petrographic analysis. Image-based methodologies applied to sections of samples reveal spatial heterogeneity and details in texture and crystallinity, whereas calorimetry-based methodologies capture the overall 'bulk sample' properties, unbiased by section effects or imaging resolution limits. These techniques are a powerful combination that can present complementary views of crystallinity. [ABSTRACT FROM AUTHOR]

Round mesas up to 500 m high occur in Martian outflow channels. Mesas in Ravi and Elaver Valles occur in deepest parts of the channels where the most intense megaflood erosion occurred. I theorize that Noachian basalts poured into craters which acted as lava traps, similar to Kilauean lava lakes. Subsequent flood basalts buried the infilled craters. Hesperian megafloods stripped away hundreds of meters of basalts, exhuming erosion‐resistant strata. Lava solidification theory is explored to assess the role of cooling in governing the structure and strength of the Martian basalts. The postulated lava lakes that formed the Ravi Vallis mesas would have needed millennia to cool. The larger Elaver Vallis mesa may have needed up to 20,000 years to solidify. Long cooling times led to coarse, doleritic mineral textures and reduced numbers of cooling joints, greatly increasing bulk rock strength and resistance to hydrodynamic erosion. Using rock mechanics theory, cores of exhumed lava‐filled craters would have bulk rock strengths at least 5 to 30 times greater than more highly fractured basalts. Discharge hydrographs for the Morella Crater breach flood that carved Elaver Vallis peak at ∼2.1 × 107 m3 s−1. Stream power per unit streambed area ranged up to >150,000 W m−2 as the breach grew in size. The calculations provide an envelope of power sufficient to erode hundreds of meters of basalts, but not great enough to remove the large mesa. Thus the legacy of an ancient, lava‐filled crater is a high mesa on the floor of Elaver Vallis. Plain Language Summary: Flat‐topped hills stand as high as 500 m on the floors of huge river channels on Mars. These mesas should have been eroded away by the powerful floods that carved these deep channels. I propose that the mesas were once craters that were overrun and filled in by lavas. The result was deep lava lakes that took thousands of years to cool. The slow cooling reduced the number of fractures that could form in the rock, making it much stronger and able to withstand the tremendous power of floods. Thinner lava flows had covered the area before the craters formed. They had many fractures because they cooled quickly. They were then more intensely fractured by the asteroid impacts that formed the craters. Powerful floods eroded away these highly fractured rocks, leaving the strong centers of the former lava lakes as high mesas. One of these mesas stands in a channel that was eroded when a large lake in Morella Crater breached the crater's rim. That special condition made it possible to calculate how the flood power changed over time. Round mesas in other channels may have been formed within a similar range of flood power. Key Points: Mesas up to 500 m high exist on the floors of outflow channels where megaflood erosion had stripped away hundreds of meters of basaltsI propose that these mesas were Noachian‐age craters that were overrun and deeply filled by basalt flows, then later exhumed by megafloodsLava physics & rock mechanics reveal that slow cooling of these lava lakes led to minimal fractures, greatly adding to bulk rock strength [ABSTRACT FROM AUTHOR]

We present a combined geomorphologic, multispectral, and geochemical analysis of crater floor rocks in Jezero crater based on data obtained by the Mast Camera Zoom and SuperCam instruments onboard the NASA Mars 2020 Perseverance rover. The combined data from this analysis together with the results of a comparative study with geologic sites on Earth allows us to interpret the origins of rocks exposed along the Artuby ridge, a ∼900 m long scarp of lower Máaz formation rocks. The ridge exposes rocks belonging to two morphologically distinct members, Artuby and Rochette, both of which have basaltic composition and are spectrally indistinguishable in our analysis. Artuby rocks consist of morphologically distinct units that alternate over the ridge, bulbous, hummocky, layers with varying thicknesses that in places appear to have flowed over underlying strata, and sub‐planar thinner laterally continuous layers with variable friability. The Rochette member has a massive appearance with pronounced pitting and sub‐horizontal partings. Our findings are most consistent with a primary igneous emplacement as lava flows, through multiple eruptions, and we propose that the thin layers result either from preferential weathering, interbedded ash/tephra layers, ʻaʻā clinker layers, or aeolian deposition. Our analyses provide essential geologic context for the Máaz formation samples that will be returned to Earth and highlight the diversity and complexity of geologic processes on Mars not visible from orbit. Plain Language Summary: Characterization of the landing site for the Mars 2020 Perseverance rover mission yields insight into early solar system processes and provides essential context for Mars Sample Return. Here we have investigated crater floor rocks in Jezero crater that are exposed along a scarp called Artuby ridge with the Mast Camera Zoom (Mastcam‐Z) and SuperCam instruments onboard the Perseverance rover. The Artuby ridge displays a characteristically layered set of rocks with a basaltic composition that are spectrally and chemically indistinguishable in our investigation. We compare our observations from Jezero with well‐understood geologic deposits on Earth, from Hawaiʻi and New Mexico. We find that terrestrial lava flows can have complex interiors that replicate many features that we see in Mastcam‐Z images of the Artuby ridge, and thus, that the series of rocks exposed along the Artuby ridge are dominated by lava flows originating through multiple eruptions. There are a number of layers and textures of the rocks in our investigation that may not have originated as lava flows, that instead may be products of weathering, interbedding of lava and volcanic ash/tephra, or wind‐borne sediment deposition. Our results highlight the diversity of geologic units on Mars not visible from orbit. Key Points: We investigated Artuby and Rochette member rocks of the Máaz formation in Jezero crater using Perseverance's Mast Camera Zoom and SuperCam dataComplex knobbly, foliated, vesicular, and layered lithologies are most consistent with lava flows originating through multiple eruptionsThe Máaz formation in Jezero crater could be unrelated to the regional Circum–Isidis capping unit [ABSTRACT FROM AUTHOR]

A secondary objective for the Perseverance rover mission to Jezero crater, Mars, is to collect igneous rocks for analysis on Earth. The mafic crater floor unit (MFU) represents the best candidate. Ten‐meter‐scale craters on the MFU exhibit rocky ejecta, rims, and slopes that indicate resistant rock. The frequency distribution of these craters is, however, low. Comparisons of MFU craters to craters on a lava plain at the Interior Exploration using Seismic Investigation, Geodesy and Heat Transport mission (InSight) landing site reveal that the MFU lacks a granular regolith. Removal of regolith or exhumation of the MFU explains the rocky crater morphology and low density. Erosion rates, calculated using crater retention timescales of ~2.0 Ga for both locations, are 10−3 to 10−4 m/Myr. The rates derive from craters impacted into rocky materials on the MFU versus regolith at InSight. The difference in material strength, yet comparable erosion rates, requires more vigorous surface processes at Jezero relative to global averages on Mars. Plain Language Summary: Jezero crater is a 45‐km diameter impact crater on Mars. It contains a river delta and deposits that suggest that it was once filled by a lake. Jezero is the landing site for NASA's Mars Perseverance rover, scheduled to land in February 2021. A primary objective of the rover is to sample rocks to determine if Mars was once habitable for life. A secondary objective is to obtain igneous rocks, or rocks that crystallize from magma or lava. Igneous rocks can be used to provide absolute age constraints on the rocks that they surround or are contained within. The purpose of this study is to evaluate a geologic unit called the mafic floor unit that is the best candidate for sampling igneous material. Small craters that formed from meteor impacts in the floor unit are surrounded by large rocks that suggest that the material is resistant to weathering and erosion, consistent with craters impacted into hard igneous rocks or other competent material. However, the unit lacks a sand‐sized surface soil that is typical of most lava plains on Mars. Comparisons to the InSight landing site indicate that wind may be responsible for removing sandy material and exposing rock. Key Points: The mafic floor unit at Jezero crater is a morphologically resistant unitThe mafic floor unit at Jezero crater lacks a granular surface regolith like other lava plains on MarsSurface processes operate at relatively higher rates within Jezero crater compared to global averages on Mars [ABSTRACT FROM AUTHOR]

Yutu-2 – the rover from the Chang'E-4 mission – is the longest operational Lunar rover, and the first rover to land on the far side of the Moon. It is the second planetary rover to be equipped with ground-penetrating radar (GPR), one of the few in-situ geophysical techniques used in planetary exploration. Since landing in 2019, Yutu-2 has travelled more than 1 kilometre in the Von Kármán (VK) crater, and has been able to investigate the dielectric properties of the shallow Lunar ejecta using its on-board high frequency GPR channels. In this paper, we use advanced signal processing and frequency attributes to infer a detailed dielectric structure of the first ≈ 30 metres of the subsurface, providing valuable information on the ilmenite content of the landing site. Both the dielectric properties and the ilmenite content suggest a shallow sequence of Imbrian basaltic layers overlaying a low-ilmenite ejecta blanket. • Detailed imaging of layered structures at the landing site of Chang'E-4 mission. • Inferring the presence of a shallow sequence of basaltic lava layers. • Using frequency attributes to estimate the ilmenite content of subsurface layers. [ABSTRACT FROM AUTHOR]

The Aristarchus Plateau region's volcanic evolution has important implications for understanding the global history of the crustal and mantle development of the Moon. Herodotus is an Imbrian-age impact crater located on the Aristarchus Plateau, with an inclined crater floor and elevation difference of 300 m. However, the timing and emplacement scenarios by which the lava flows formed and filled the inclined crater floor remain unknown. In this paper, remote sensing images and topographic profiles are used to analyze the emplacement time and lava flow–filling scenarios for Herodotus crater. The lava flows may have begun to fill Herodotus crater at 3.7 Ga and no later than Eratosthenian. Multiple volume-limited lava flows and pre-eruption topography are two possible scenarios for the formation of the inclined crater floor. Analysis of the morphology of the inclined crater floor provides key information about lunar volcanic processes in the Aristarchus Plateau. • Herodotus crater offers insight into local volcanic processes in the Aristarchus Plateau. • Herodotus crater has an inclined crater floor with elevation difference of 300 m. • The inclined crater floor of Herodotus may be formed by either multiple volume-limited lava flows or pre-eruption topography. [ABSTRACT FROM AUTHOR]

We present the results of our studies of the rheological properties and ages on Alba Mons lava flows. Previous studies have shown that the rheology of lava flows, such as yield strength and viscosity, as well as external parameters affecting flow characteristics, such as effusion rate and eruption duration can be derived by remotely sensed dimension measurements. The calculations made in this study are based on images obtained from the Context Camera (CTX) on board of NASA's Mars Reconnaissance Orbiter (MRO) as well as data from the Mars Orbiter Laser Altimeter (MOLA) on NASA's Mars Global Surveyor (MGS). Absolute model ages (AMAs) have been derived by performing crater size-frequency distribution (CSFD) measurements on CTX images. The main objectives of this investigation are not only the calculation of the rheological properties and ages, but also the analysis of possible correlations between the rheologies, ages and distances of the flows to the volcano's center. A comparison of the rheological properties of the investigated lavas with those reported for flows on other planetary bodies was also performed. The aim of the study is a better insight into the history of one of the largest volcanoes in the Solar System. We provide new information about the formation and composition of the volcano's lava flows, whether they changed over time, and until when Alba Mons has been active. In total, 29 lava flows close to the summit of Alba Mons were mapped and measured. The calculated yield strengths are 2.79 × 103 Pa on average, ranging from 4.00 × 102 Pa to 9.61 × 103 Pa. We found effusion rates between 46 m3 s−1 and 1528 m3 s−1 with an average effusion rate of 636 m3 s−1. The derived viscosity is on the order of 1.04 × 107 Pa s with values between 1.27 × 105 Pa s and 1.0 × 108 Pa s. The lavas have erupted over a period of 11 to 223 days, with an average eruption duration of 68 days. The rheological properties derived in this investigation are very similar to those of other volcanic regions on Mars, especially Elysium Mons and Elysium Planitia. However, they differ from calculated rheologies of previous studies of venusian lavas and lunar lava flows. Based on the derived yield strength and viscosity values, the composition of the lava flows can be inferred as basaltic/basaltic-andesitic, which is analog to terrestrial basaltic or andesitic a'a lava flows. Significant correlations between the rheological properties and the distance to Alba Mons' center have not been found. AMAs could be derived for 14 of the 29 lava flows investigated, because 15 lava flows have either reached the state of equilibration or have too few impact craters to derive reliable model ages. The AMAs range from 130 ± 40 Ma to 810 ± 60 Ma. The results indicate a late volcanic activity at Alba Mons. Correlations between the AMAs and distance to the volcano's center, as well as between the rheological properties and AMAs were not observed. • 29 lava flows close to the summit of Alba Mons were mapped. • We derived rheological properties and flow characteristics for the 29 lava flows. • The derived properties indicate that the lava flows are basaltic/basaltic-andesitic in composition. • The lava flows are most similar to terrestrial basaltic or andesitic a'a lava flows. • We found young absolute model ages (AMAs) ranging from 130 ± 40 Ma to 810 ± 60 Ma, indicating a late activity of Alba Mons. [ABSTRACT FROM AUTHOR]

Abstract: A ‘rimless depression’ 100 km inside the southwest rim of the Caloris basin is revealed by high resolution orbital imaging under a variety of illuminations to consist of at least nine overlapping volcanic vents, each individually up to 8 km in diameter. It is thus a ‘compound’ volcano, indicative of localised migration of the site of the active vent. The vent floors are at a least 1 km below their brinks, but lack the flat shape characteristically produced by piston-like subsidence of a caldera floor or by flooding of a crater bottom by a lava lake. They bear a closer resemblance to volcanic craters sculpted by explosive eruptions and/or modified by collapse into void spaces created by magma withdrawal back down into a conduit. This complex of overlapping vents is at the summit of a subtle edifice at least 100 km across, with flank slopes of about only 0.2 degrees, after correction for the regional slope. This is consistent with previous interpretation as a locus of pyroclastic eruptions. Construction of the edifice could have been contributed to by effusion of very low viscosity lava, but high resolution images show that the vent-facing rim of a nearby impact crater is not heavily embayed as previously supposed on the basis of lower resolution flyby imaging. Contrasts in morphology (sharpness versus blurredness of the texture) and different densities of superposed sub-km impact craters inside each vent are consistent with (but do not prove) substantial differences in the age of the most recent activity at each vent. This suggests a long duration of episodic magmagenesis at a restricted locus. The age range cannot be quantified, but could be of the order of a billion years. If each vent was fed from the same point source, geometric considerations suggest a source depth of at least 50 km. However, the migration of the active vent may be partly controlled by a deep-seated fault that is radial to the Caloris basin. Other rimless depressions in this part of the Caloris basin fall on or close to radial lines, suggesting that elements of the Pantheon Fossae radial fracture system that dominates the surface of the central portion of the Caloris basin may continue at depth almost as far as the basin rim. [Copyright &y& Elsevier]

Abstract: The origin of Mars’ Elysium-Amazonis plain has been the subject of debate for three decades, with a flood-volcanic origin the majority view today. Stratigraphical observations indicate that this view, based mainly on form analogy with Earth, is in error. A general unwillingness to engage with these observations in published work is detrimental not only to wider perceptions of planetary geology, often viewed as little more than the science of resemblance as a consequence, but also to superposed theories of surface chronology and source of the young martian meteorites, which are characterised by inconsistency and paradox as a result. Adherents to the volcanic hypothesis must convincingly explain how the observed field-relations are consistent with a lava surface across this region, or accept that these deposits are not what they currently believe them to be. [ABSTRACT FROM AUTHOR]

• Seismic data capture 10-20 s lava lake sloshing modes during 2018 Kilauea eruption. • A horizontal force and a volume change explain sloshing mode displacements. • Sloshing modes put lower bounds on reservoir storativity. Basaltic volcanoes like Kīlauea, Hawai'i, pose hazards through lava flows and other eruptive activity. Quantifying hazard requires constraining the volume of magma stored in shallow reservoirs, as well as the capacity of those reservoirs to accumulate and discharge magma in response to pressure changes (i.e., storativity). Shallow reservoirs are often connected through magmatic conduits to lava lakes, which are frequently perturbed by rockfalls, convection, and outgassing. Here we present a novel method to quantify reservoir storativity at Kilauea that exploits the seismically observable oscillatory response of the lake-conduit-reservoir system to perturbations during the May 2018 eruption. Seismic events recorded by the summit broadband seismometer network during the eruption feature multiple oscillatory modes in the very long period (VLP) band. The longest period mode (∼30-40 s, here termed the conduit-reservoir mode) persisted during drainage of the lava lake, indicating its primary association with the underlying conduit-reservoir system. Additional modes, with periods of 10-20 s, vanished during lake drainage and are attributed to lava lake sloshing. The surface displacements of the two longest period sloshing modes are explained as the superimposed response to a near-surface horizontal force along the axes of the crater (from the pressure imbalance during sloshing on the crater walls) and a volume change in a reservoir located at the conduit-reservoir mode source centroid. Both sloshing modes are in the "deep-water" surface gravity wave limit where disturbances are largest near the lake surface, though pressure changes on the top of the conduit at the lake bottom provide the observed excitation of the underlying conduit-reservoir system. Combining magma sloshing dynamics in the crater and a conduit-reservoir oscillation model, we bound the storativity of the reservoir to be greater than 0.4 m3/Pa. This implies a storage volume of a few km3 for an approximately equidimensional (e.g., spherical) reservoir. A smaller volume is possible but requires the presence of other shapes of magma bodies, such as sills or dikes, and/or significant finite source effect. Our work demonstrates the signature of lava lake sloshing modes in the seismic data and the potential of these modes in constraining the structure of the shallow magmatic system. [ABSTRACT FROM AUTHOR]

Gale crater shows infilling of lava of basaltic origin mainly coming from the south via Farah Vallis. Using available Thermal Emission Imaging System (THEMIS) images, Mars Orbiter Laser Altimeter (MOLA) topographic data, Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) mineralogical data, and geochemical analyses taken in situ by the Mars Science Laboratory (MSL) in different locations of the crater, we focused on the possible origin and the main path of the lava that filled Gale crater. We found that: 1) the K/Ar age of the basaltic rocks on Gale's floor is consistent with the age of formation of Tyrrhenus Mons derived from the southern polar giant impact (SPGI) model; 2) the Aeolis Mensae region does not show evidence for interaction between lava coming from the north (Elysium Mons) and lava coming from the south (Tyrrhenus Mons); 3) the geomorphological analysis shows that Farah Vallis is the convergence of a complex network of volcanic channels that can be tracked back to the lava fields of Tyrrhenus Mons; 4) a one-dimensional model of lava along the observed path, using an Adirondrack basalt composition for the substrate, shows that lava from Tyrrhenus Mons is thermally capable of flowing the entire distance to Gale before cooling down. This evidence is consistent with the lava fill observed at Gusev crater. • Gale crater is filled by low viscosity basaltic lava, similar to Gusev crater. • Lava traveled from Tyrrhenus Mons directly to Gale crater. • Farah Vallis is the main entrance for lava coming from Tyrrhenus Mons. • Computer simulations are consistent with the presented geological observations. [ABSTRACT FROM AUTHOR]