Pit Chains Research Articles

Analysis of faults and pit chains in Noctis Labyrinthus: Implications for early extension and possible magmatic plumbing

Noctis Labyrinthus has been a region of disputed origin due to its complexity and poor understanding of how various processes and mechanisms may have combined to form it. The surface is an integrated record of intensive tectonic activity expressed by a multiple extended sets of dip-slip faults oriented in different directions, and thought to have acted on this region over its history. These faults are always coalescent to pits and pit chains displaying a complicated geological history in the region. To understand this geological history, we mapped the surface features in Noctis Labyrinthus using the High-Resolution Stereo Camera (HRSC) onboard Mars Express ND2 nadir channel basemaps, and we adapted the Digital Terrain Map (DTM) from the Mission Experiment Gridded Data Record (MEGDR) of Mars Orbiter Laser Altimeter (MOLA) onboard Mars Global Surveyor (MGS) for the topography. We have investigated the spatial distribution and trend of fault systems, the pit chains' morphology, and the correlation between these two types of features. Our results show three fault systems: i) NS and NNE-SSW, ii) EW and ENE-WSW, and iii) NNW-SSE and NW. The analysis of the faults trending, cross-cutting correlation and the superimposition led to identify multiple intersections between these faults that have been alongside with the reactivations of some inherited faults. We interpreted the first system of fault to be related to coeval lateral extension, generated by regional stress tensor, which is probably related to the slight bending of Valles Marineris within two phases of bidirectional extension. The second system of faults has been generated by the radial oblate stress tensor related to the formation of the small shield volcanoes in Syria Planum. However, the third system is likely related to the external driving process, probably in the Tharsis province. We classified pits in four evolutionary stages based on their morphometric attributes. We believe that the formation of the pit chains in Noctis Labyrinthus is related to a surface collapse after a pressure drop related to the magma chamber deflation associated with Syria Planum volcanic province. We propose a deformational model based on early extension and magmatic plumbing as driving processes for the formation of Noctis Labyrinthus.

The continuation of the Mull Dyke Swarm into the Southern North Sea

We present new geophysical observations of the Mull Dyke Swarm in the Southern North Sea. Two- and three-dimensional seismic reflection and aeromagnetic data were used to map the dykes. The three main dyke groups recognized onshore (Cleveland, Blyth and Hawick–Acklington) are found to extend to varying distances into the North Sea, crossing a number of major crustal-scale fault zones and domain boundaries, with almost no reorientation. The Blyth Dyke Group extends furthest, for a distance of 672 km from the source on Mull. The seismic data show extensive development of pit chain craters above the upper tips of these dykes, which can be approximately dated to the late Paleocene from the ages of crater fills. Volumetric estimates are made of the intrusive volumes associated with each group, ranging from 90 to 202 km 3 . These three main axes of intrusion probably formed in different intrusive events within a c. 1 myr period, from 59 to 58 Ma, during magnetic chron C26R.

Unveiling the Subsurface of Late Amazonian Lava Flows at Echus Chasma, on Mars

The Echus-Kasei region on Mars has been exposed to different episodic volcanic, fluvial, and glacial events in Amazonian time. The goal of the present work is to demonstrate the usefulness of radar instruments to find preserved late Amazonian subsurface structures that may have been encapsulated underneath recent lava flows on Mars. We have analysed 27 radar observations of the SHAllow RADar (SHARAD) instrument on board the Mars Reconnaissance Orbiter (MRO), over the region of Echus Chasma. We discovered the presence of subsurface reflectors in five consecutive SHARAD radargrams at a depth from 35 to 79 m beneath the structure of a lava fan that formed about 59 ± 4 Ma ago. Some vents are preserved above the surface of this lava flow, which stands at a height of 80 m above the surrounding surface. A few kilometres to the north, we find other subsurface reflectors at a depth of about 30 m and a long pit chain formed by the collapse of a lava tube. These kinds of subsurface late Amazonian structures are of interest for astrobiology because they date from the last period when the planet still experienced intense volcanic activity over regions that were previously extensively covered by water.

Subglacial catastrophic-flood origin of linear and curvilinear flat-rimmed pit chains on Mars: Evidence from geomorphological mapping and detailed landsystem analysis

Flat-rimmed pits lacking emanating flow-like features on pit margins are typically clustered as linear or curvilinear chains on Mars. Their formation has been attributed to faulting, volcanism, or roof collapse of subsurface voids. Here we test these end-member models by conducting landform analysis and systematic geomorphological mapping in the central Tharsis region. Our work shows that the mapped flat-rimmed pit chains were formed on a lava-plain landscape that is mantled by a surficial meter-sized boulder layer. The flat-rimmed pit chains are closely associated with a landform assemblage consisting of localized pit-linking/terminating dendritic networks of gullies, U-shaped troughs, isolated sinuous channels, sinuous round-topped boulder-bearing ridges, and rampart craters. The absence of pit-bounding and pit-cutting faults rules out the faulting origin, while the lack of rubble-filled pit floors and erupting flow-like landforms does not favor the volcanic and roof-collapse mechanisms. When viewed together, the mapped flat-rimmed pit chains and their closely associated landform assemblage can be explained by a glacial-landsystem model: (1) pits were created by vortex-induced erosion during repeated, violent, catastrophic mega-flooding below a regionally extensive ice sheet possibly covering the entire Tharsis region (i.e., the Tharsis ice cap), (2) the subglacial floods exploited bedrock and/or ice sheet fracture sets resulting in linear and parallel chains, (3) localized pit-linking and pit-terminating U-shaped troughs and round-topped boulder ridges represent subglacial channel bodies including glacial eskers, (4) surficial boulders represent glacial deposits, (5) local trough-bounded pit chains resemble coulees and their hosted rock basins on Earth, and (6) rampart craters with viscous-flow ejecta deposits represent surface or near surface ice generated by the inferred glaciation. We suggest that the excavated pit material was transported by subglacial megafloods along the giant (>6000 km long) circum-Tharsis outflow channels to the outwash plains in the northern-hemisphere lowlands.

Long‐Lived and Continual Volcanic Eruptions, Tectonic Activity, Pit Chains Formation, and Boulder Avalanches in Northern Tharsis Region: Implications for Late Amazonian Geodynamics and Seismo‐Tectonic Processes on Mars

AbstractTharsis is the largest volcanic province on Mars. It consists of a few large shield volcanoes, one of which is Alba Mons (AM), located in northern Tharsis, with the Ceraunius Fossae (CF) graben system to the south of it. Previous workers argued in favor of episodic building of Tharsis volcanoes. In contrast, we show that volcanism in the AM and CF regions occurred continually, at least in the last few hundred million years, based on ages of >1,000 stratigraphically young lava flows. Central volcanism in AM terminated around 200 Ma, while subsequent young volcanism, fed by both small shields and fissures, migrated to the south in CF. Several generations of grabens hosting thousands of simple to complex pit chains were formed by magmatic intrusion through feeder dikes, and these activities also migrated to the south during the Late Amazonian epoch. Thousands of boulder avalanches mark the slopes of grabens, pit chains, and impact craters, with ages ranging from a few tens to thousands of years. The local geological settings of the boulder falls suggest that both tectonic and volcanic marsquakes triggered the boulder avalanches. The broad zone of boulder falls in northern Tharsis defines the potential epicentral zone of (MW 4.1) 18 September 2021 marsquake. We infer that long‐lived and active magma chambers and subcrustal magma underplating driven by a mantle plume are present beneath the AM volcano and that these probably migrated south toward CF in the Late Amazonian epoch.

Measurements of regolith thicknesses on Enceladus: Uncovering the record of plume activity

Tectonic pit chains are geologic landforms that form in loose unconsolidated regolith and are observed on many solar system bodies. In the outer solar system pit chains are most clearly observed on Enceladus. In this paper, we test three techniques for using pit chain morphometry to probe the regolith thickness across Enceladus accumulated as fall-back from its plume eruptions. We favor the precision of the Slope Angle Method (SAM), allowing for spatially related heterogeneities in regolith characteristics, and we measured regolith thicknesses up to 700 m (mean = 250 m, n = 116). We combine models of plume deposition rates with observed regolith thicknesses and assume lunar-like crater-generated regolith production. We constrain the time needed to deposit the observed sequences of regolith to extrapolate the age of the plume source and its liquid reservoir. The porosity and density of the plume-generated regolith are unconstrained parameters that affect the rate at which the regolith is deposited. Assuming a constant deposition mass flux, we explored the parameter space of regolith density (0.02–0.92 g/cm3) and porosity (0–90%) that would deposit a thick enough regolith to match the pit chain observations. Only by using the lowest density (0.2 g/cm3) and highest porosity (90%) are we able to reproduce the maximum regolith thicknesses within the age of the solar system. We interpret the long deposition times needed to match regolith thicknesses to suggest that Enceladus's mass flux from the plume needs to have been significantly higher, that the regolith is possibly a low-density/high-porosity material, and/or additional regolith-forming processes (like alternative vent localities) exist, or have existed.

Spectral Analysis of Ceres’ Main Linear Features

Linear features are very common on asteroid surfaces. They are generally formed after impact and provide information about asteroid evolution. This work focuses on a mineralogical and spectral analysis of the main linear features on the 1/Ceres surface, having both tectonic (Samhain Catena’s pit chains) and geomorphic origins, i.e., generated by ejecta material (Occator ejecta, Dantu’s secondary radial chains, secondary radial chains generated from the Urvara impact). The analysis is based on spectral parameters defined by the Dawn’s VIR imaging spectrometer data, as albedo and depths of the bands centered at approximately 2.7, 3.1, 3.4 and 3.9 mm. The geomorphic linear features show spectral variations with respect to the surroundings, i.e., ammoniated phyllosilicates band depth shallowing is caused by the presence of material originating in a different region or dehydration caused by impact. The Samhain Catena does not show any mineralogical variation, due to its tectonic origin. The spectral behavior of Ceres’ linear features is similar to that observed on other asteroids (Vesta, Eros) and can be diagnostic in discerning the origin of linear features. Then, we searched spectral signatures of organics in the Samhain Catena region, since they are expected to form at depth due to internal processes: the absence of such signatures indicates that either they form at a larger depth or that their subsurface distribution is uneven.

Distinctive iceberg ploughmarks on the mid-Norwegian margin: Tidally influenced chains of pits with implications for iceberg drift

ABSTRACT Curvilinear depressions and chains of asymmetrical to circular pits up to a few meters deep and a few tens of meters wide have been mapped on the upper continental slope beyond the mid-Norwegian shelf. These features are interpreted to represent a continuum of seafloor landforms produced by the grounding of iceberg keels at successive low tides. The features occur along a 50 km long stretch of the upper slope in modern water depths between 400 and 500 m. The average distance between pits varies between about 70 and 175 m, representing one tidal cycle of 12 hr 25 min between successive low tides. This yields average iceberg drift velocities of between 5 and 15 m hr−1. The pits are often asymmetrical, with a downstream surcharge or berm, making it possible to determine the direction of iceberg drift and, therefore, the current direction at the time of ploughmark formation. The c. 300 m thick icebergs producing the ploughmarks are likely to have been sourced mainly from the fast-flowing Norwegian Channel Ice Stream to the south and probably formed during the early part of regional deglaciation of the Norwegian shelf after the Last Glacial Maximum around 20,000 years ago. The icebergs appear to follow a similar northeastward flow direction to that of the present Norwegian Atlantic Current offshore of Norway.

A fossil carbonate rocky shore in the Kalcit Quarry: a new insight into echinoid shallow marine bioerosion (Miocene; Czech Republic)

ABSTRACT A Miocene fossil rocky coastline is well preserved in Kalcit Quarry near Brno. It differs from the few preserved coeval coastlines of the Central Paratethys in the dominance of borings attributable to echinoids. These borings are represented by roughly smooth shallow circular pits interpreted as dwelling traces of echinoids. Ichnotaxonomically, they can be placed in the ichnospecies Circolites kotoucensis Mikuláš, 1992. Besides usual individual pits, two discernible varieties of composite Circolites were found: (1) linear chains of pits interconnected by a smoothed joint bottom; and (2) spirally folded pits resembling a rosacean flower. The linear chains are morphologically very similar to narrow forms of Planavolites homolensis Mikuláš, 1992 and to Ericichnus bromleyi Santos and Mayoral, 2015. This similarity demonstrates the necessity of a review of the diagnoses of all the hitherto described ichnogenera attributed to boring echinoids, i.e., Circolites, Ericichnus, and Planavolites. We suggest that linear or planar traces with smoothed bottoms should be considered a composite of neighbouring Circolites, provided that the remains of individual pits are still discernible in the ground plan. Ericichnus is now considered as junior synonym of Planavolites Mikuláš, 1992.

Volcano dynamics vs tectonics on Mars: evidence from Pavonis Mons

Volcanic activity is widespread within the inner Solar system and it can be commonly observed on rocky planets. In this work, we analyse the structures of Pavonis Mons in the Tharsis volcanic province of Mars by performing structural mapping, azimuth, and topographic distribution of linear features on the flanks of Pavonis, such as grabens and pit chains. We tested whether their formation is to be ascribed to the volcano dynamics and magmatic activity or the tectonics. Through the length size distribution and fractal clustering analyses of the structural features, we found that large grabens are vertically confined in the upper mechanical layers of the brittle crust whereas pit chains penetrate the whole crust up to the magmatic source, indicating that they can be considered the main feeders of Pavonis Mons. We inverted the topography with dykes and faults models to test whether grabens at the surface are the expression of intrusions at depth and we suggest that thin dykes inducing normal faulting are the most likely mechanism. Furthermore, two azimuthal distribution of the grabens are identified: concentric grabens occur on the volcano summit while linear grabens at its base show NE-SW trend as the Tharsis Mons volcanos alignment. The occurrence of linear grabens suggests that Pavonis likely experienced a phase of active rifting with the formation of such structures, followed by a phase of volcano growth and concentric magma intrusions when volcano and magma chamber dynamics prevailed.

Tectono‐Magmatic, Sedimentary, and Hydrothermal History of Arsinoes and Pyrrhae Chaos, Mars

AbstractArsinoes and Pyrrhae Chaos are two adjacent chaotic terrains located east of Valles Marineris and west of Arabia Terra, on Mars. In this work, we produced a morpho‐stratigraphic map of the area, characterized by a volcanic bedrock disrupted into polygonal mesas and knobs (Chaotic Terrain Unit) and two nondisrupted units. The latter present a spectral variation, likely associated with hydrated minerals, and they are here interpreted as sedimentary units. The reconstructed geological history of the area starts with the emplacement of the basaltic bedrock, followed by the collapse that caused the formation of the chaotic terrains. Since evidences of volcano‐tectonic activity are widespread across the area (e.g., fissure vents/graben, radial and concentric systems of faults, y‐shaped conjunctions, lava flows, and pit chains), and an intricate system of lava conduits is hypothesized for the occurrence of such features, we propose the possibility that the whole collapse was caused primarily by volcano‐tectonic processes. In a late stage, after the end of the volcano‐tectonic activity, a lacustrine/evaporitic depositional environment could have set, with the deposition of the nondisrupted units. The hydrated minerals found in the periphery of the Chaos could be the result of hydrothermal alteration of the basaltic bedrock.

Origins of pits and troughs and degradation on a small primitive planetesimal in the Kuiper Belt: high-resolution topography of (486958) Arrokoth (aka 2014 MU69) from New Horizons

The dominant topographic features on two-lobed Kuiper Belt object (486958) Arrokoth (provisionally designated 2014 MU69) are scattered, small, circular depressions or pits up to ~1.0 km across and curvilinear troughs observed near the terminator during the New Horizons encounter of 01 January 2019. With important exceptions, evidence for an endogenic origin for pits is lacking and impact remains the most likely origin. Pit depths relative to the local surface are shallower than hypervelocity simple craters on icy moons and consistent with low velocity (~300 m/s) impacts in an icy target (the role of porosity and cohesion in cratering on Arrokoth being uncertain). There is, however, a large scatter in observed d/D, with some pits too shallow to measure reliably. The range of preservation states observed for both pits and troughs is consistent with slow but persistent degradation on the surface of this (and perhaps other) small primitive planetesimal(s) in the Kuiper Belt by agents such as micrometeorite bombardment or volatile loss, indicating that degradation does indeed occur on such bodies. Arrokoth pits could also be related to circular depressions on comet 9P/Tempel (though comparisons of surface features on Arrokoth and comets are intriguing they are limited by resolution differences and the evolved state of cometary surfaces). Two of the curvilinear troughs occur along the terminator of the Large Lobe. One trough is a shallow depression devoid of resolvable structures, the other features several linear scarps a few 10s of meters high, suggesting that coherent failure can occur on the surfaces of small Kuiper Belt objects such as Arrokoth. Several of the deepest small pits are also clustered within this walled trough, similar to tectonically associated pit chains on other planets. These pits and an obliquely viewed linear chain of elongate depressions remain the best candidates for endogenic features on Arrokoth. Subtle undulations and linear features no more than a few 10's of meters in amplitude (and even a few candidate positive relief features) are also evident in the terminator regions, indicating that the long-term evolution of this body may have been complex.

Icelandic Pit Chains as Planetary Analogs: Using Morphologic Measurements of Pit Chains to Determine Regolith Thickness

AbstractPit chains are distinctive geologic landforms present on planetary bodies across the solar system, which can be used to understand regolith properties and formation. If there is a direct relationship between pit diameter and the regolith depth, pit chains can be used to map regolith thickness across a planetary surface. Here, the morphology of individual pits within pit chains in northern Iceland was measured as a planetary analog to determine whether there is a direct relationship between individual pit diameters and pit depth, which is assumed to be a proxy for regolith depth. The morphology of pit chains and regolith thickness was measured in three different locations in northern Iceland, within two different substrates: unconsolidated floodplain sediments and more consolidated soils overlaying basaltic lava flows. There is a significant linear relationship between pit diameter and depth for pit chains located in the floodplain sediment, but not for pits located in basaltic materials. However, this depth‐diameter relationship does not correlate with regolith thickness. The depth of the pits in basaltic materials is more representative of the regolith depth than the pits in the floodplain sediments. If high‐resolution topography data are available, then the depth of pits in more consolidated materials can be used as a reliable estimate of regolith thickness. In more unconsolidated materials, the pit depth represents a minimum regolith depth. This ability to resolve regolith thicknesses may help resolve the processes by which regolith is emplaced and has implications for the thermal evolution of planetary bodies.

Evidence of thrust faulting and widespread contraction of Ceres

The surface of the dwarf planet Ceres is considered to be dominated by geological processes typical of small bodies or medium-sized icy bodies, such as impact cratering1,2; there are also features of putative cryovolcanic origin3 as well as those related to flow of near-surface ice4. Extensional features4–6 include regional linear troughs, fractures and pit chains, fractures associated with impact craters and with crater floors, and polygonal craters whose walls seem to be structurally controlled. However, no contractional features, which are related to thrust fault activity more typical of large silicate bodies7–11, have been described. Here we report the presence of scarps, ridges and fractures associated with thrust faults, tectonically raised terrains and thrusted craters—all contractional features. These structures closely resemble thrust-fault-related lobate scarps on Mercury7,8 and Mars9,10, albeit with lower displacement. They seem more abundant in high-latitude ancient terrains, perhaps owing to illumination effects that aid identification. The observed deformation implies that the crustal material is stronger than water ice but weaker than silicate rocks, consistent with our current knowledge of crustal composition12 and rheology13. These features suggest that large-scale contraction, possibly related to differentiation processes, occurred in the history of Ceres. Contractional features such as scarps, ridges and fractures from thrust faults are typical of large silicate bodies such as Mercury and Mars. Evidence for similar features on Ceres suggests the possibility of large-scale contraction on this icy body.

Ceres’ Ezinu quadrangle: a heavily cratered region with evidence for localized subsurface water ice and the context of Occator crater

Dawn is the first spacecraft to visit and orbit Ceres, the largest object in the asteroid belt and the only dwarf planet in the inner Solar System. The Dawn science team undertook a systematic geologic mapping campaign of Ceres’ entire surface. Here we present our contribution to this mapping campaign, a geologic map and geologic history of the Ezinu quadrangle, located in the northern mid latitudes from 21–66° N and 180–270° E. From our map, we reconstruct the geologic history of Ezinu quadrangle, which is dominated by impact cratering. Large impact craters that formed a few hundreds to tens of millions of years ago, such as Datan, Messor, Ninsar and Occator, are surrounded by ejecta and contain the products of mass wasting (hummocky crater floor material and talus material) and crater-wall collapse (terrace material). Two of these large impact craters are the sources of lobate flows, which we interpret as melt flows emplaced after the ballistically deposited ejecta. Morphological evidence suggests these lobate flows are rich in water–ice-bearing material that was excavated during the formation of the impact craters. There are only a few localized occurrences of lobate flows, suggesting that the water–ice-bearing source materials have restricted extents and/or are deeply buried within Ceres’ subsurface. The quadrangle also contains a variety of linear features: secondary crater chains are formed by the impact of locally and globally sourced material and pit chains and grooves are formed by the collapse of surficial materials into sub-surface fractures. The Ezinu quadrangle contains the northern portion of Occator crater, which is the host crater of prominent bright regions called faculae. Our geologic analysis therefore also provides context for the future investigation of Occator and its intriguing faculae.

Evidence for the Interior Evolution of Ceres from Geologic Analysis of Fractures

AbstractCeres is the largest asteroid belt object, and the Dawn spacecraft observed Ceres since 2015. Dawn observed two morphologically distinct linear features on Ceres's surface: secondary crater chains and pit chains. Pit chains provide unique insights into Ceres's interior evolution. We interpret pit chains called the Samhain Catenae as the surface expression of subsurface fractures. Using the pit chains' spacings, we estimate that the localized thickness of Ceres's fractured, outer layer is approximately ≥58 km, at least ~14 km greater than the global average. We hypothesize that extensional stresses, induced by a region of upwelling material arising from convection/diapirism, formed the Samhain Catenae. We derive characteristics for this upwelling material, which can be used as constraints in future interior modeling studies. For example, its predicted location coincides with Hanami Planum, a high‐elevation region with a negative residual gravity anomaly, which may be surficial evidence for this proposed region of upwelling material.

Pit chains on Enceladus signal the recent tectonic dissection of the ancient cratered terrains

Enceladus is the first outer solar system body on which pit chains have been positively identified. We map the global distribution of pit chains and show that pit chains are among the youngest tectonic features on Enceladus's surface, concentrated in the cratered plains centered on Enceladus's Saturnian and anti-Saturnian hemispheres. Pit chains on Enceladus are interpreted as the surface expressions of subsurface dilational fractures underlying a cover of unconsolidated material, which we infer to be a geologically young cover of loose regolith that mantles the surface of Enceladus. A widespread layer of regolith may act to insulate the surface, which has implications for the thermal state of Enceladus's ice shell. The widespread distribution of pit chains across the cratered plains indicates that this ancient surface has recently been tectonically active.

Pit Chains Belonging to Radiating Graben‐Fissure Systems on Venus: Model for Formation during Lateral Dyke Injection

Acta Geologica Sinica - English EditionVolume 90, Issue s1 p. 143-144 6 Emplacement mechanism of dykes Pit Chains Belonging to Radiating Graben-Fissure Systems on Venus: Model for Formation during Lateral Dyke Injection Calder W. PATTERSON, Calder W. PATTERSON Department of Earth Sciences, Carleton University, Ottawa, K1S 5B6 CanadaSearch for more papers by this authorRichard E ERNST, Corresponding Author Richard E ERNST Richard.Ernst@ErnstGeosciences.com Department of Earth Sciences, Carleton University, Ottawa, K1S 5B6 CanadaCorresponding author. E-mail: Richard.Ernst@ErnstGeosciences.comSearch for more papers by this authorClaire SAMSON, Claire SAMSON Department of Earth Sciences, Carleton University, Ottawa, K1S 5B6 CanadaSearch for more papers by this author Calder W. PATTERSON, Calder W. PATTERSON Department of Earth Sciences, Carleton University, Ottawa, K1S 5B6 CanadaSearch for more papers by this authorRichard E ERNST, Corresponding Author Richard E ERNST Richard.Ernst@ErnstGeosciences.com Department of Earth Sciences, Carleton University, Ottawa, K1S 5B6 CanadaCorresponding author. E-mail: Richard.Ernst@ErnstGeosciences.comSearch for more papers by this authorClaire SAMSON, Claire SAMSON Department of Earth Sciences, Carleton University, Ottawa, K1S 5B6 CanadaSearch for more papers by this author First published: 31 October 2016 https://doi.org/10.1111/1755-6724.12937Citations: 3AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume90, Issues1Special Issue: The Seventh International Dyke Conference: Dyke Swarms: Keys to Paleogeographic Reconstruction IDC7, 18–20 August, BeijingOctober 2016Pages 143-144 RelatedInformation

A network of lava tubes as the origin of Labyrinthus Noctis and Valles Marineris on Mars

The role of lava tube networks and lava channels is reassessed as the primordial stage of the volcano-erosional processes that formed the Labyrinthus Noctis–Valles Marineris system instead of a tectonic origin. The combined use of CTX, CRISM, HiRISE imagery, and MOLA profiles has provided valuable insight in the evolution of pit chains into fossae first and then chasmata later due to mass wasting processes caused by the erosional effect of the lava flows that draped Valles Marineris and other outflow channels. Although a quantitative evaluation of eruption rates is difficult even with digital terrain models (DTMs) because of the mixing between new flows and paleoflows, a comparison with Elysium and other Tharsis outflow channels suggests that the availability of lava supply is correlated to their widths. The images of ubiquitous lava flows rather than sporadic light-toned deposits strengthen the role of lava over that of water in the erosional processes that formed Labyrinthus Noctis and carved Valles Marineris like many other outflow channel on Mars. The erosional evolution of the outflow channels shows an increasing trend of age and a decreasing trend of depth from the sources on Tharsis to the mouths at Chryse Planitia. This finding, coupled with the observation of lava flows mantling Chryse Planitia, may have profound implications for the water inventories thought to have filled the lowlands with an ocean.

Coseismic, dilational-fault and extension-fracture related pit chain formation in Iceland: Analog for pit chains on Mars

Pit crater chains are common topographic features on Mars and several other planetary bodies, and a wide range of mechanisms has been proposed for their origin. Two rifting-related seismic events in 1975–1976 and 1978 along the Mid-Atlantic Ridge near the northern coast of Iceland, associated with the Krafla volcanic eruptions to the south, produced an array of pit chains in unconsolidated sediments overlying Holocene basalt flows. Fault scarps and extension fractures in basaltic lava flows are traceable laterally into overlying unconsolidated fluvial deposits, revealing contrasting deformation styles in the two mechanical layers. Map-scale structures in basalt with little or no sedimentary cover include (1) fault scarps, (2) extension fractures and fracture swarms, (3) faulted monoclines, (4) widened fractures with caverns, and (5) localized circular or elongate collapse pits. Where unconsolidated fluvial sand and gravel deposits >3 m thick cover the basaltic lava flows, structural geomorphic features are dominated by (1) grabens bounded by normal faults with ∼1 m displacement, (2) cone- to bowl-shaped pit craters with depths up to 2.8 m, and (3) elongate troughs. Formation of these structures in fluvial sediment was triggered by reactivation of faults and extension fractures in the underlying basalt. Pit craters are readily explained by downward “draining” of poorly consolidated material into subterranean cavities produced by fault and extension fracture dilation in underlying cohesive material (basalt). High-resolution imagery on Mars shows geomorphic patterns that are directly analogous to these Icelandic pit chains, suggesting similar processes have occurred on Mars.