1,721,374 research outputs found
Large scale fault kinematic analysis in Noctis Labyrinthus (Mars)
No full textNoctis Labyrinthus (Mars) is characterized by many tectonic features, which represent brittle deformation of the crust. This tectonic setting was analysed by remote sensing of the Viking Mars Digital Image Model (MDIM) mosaic and Mars Orbiter Camera (MOC) global mosaic, in order to identify deformational events. The main features are normal faults producing horst-graben structures, strike-slip faults,
and related en-echelon and pull-apart basins. Using the criterion of cross-cutting relationships and analysis of secondary structures, to infer sense of movement of faults, two deformational phases were identified in the Noctis Labyrinthus area. The first, D1, located mainly in the
northern part, is characterized by transtensional faults (Noachian). The second, D2, recorded in the southern part of the Noctis Labyrinthus by an orthorhombic extensional fault pattern along NNE and WNW trends, is related to the Valles Marineris formation (Late Noachian–Early Hesperian). A third tectonic event, D3, represented by the partly known dextral NW strike-slip faults cross-cutting the Valles Marineris Canyon System (Late Hesperian?-Amazonian?), was not found in Noctis Labyrinthus at the scale and resolution considered
Tectonisation of basin edges on Mercury
No full textLobate scarps on Mercury are generally accepted to be surface expressions of thrust faulting. This is taken as evidence
of lithospheric contraction on a global scale, reflecting either global cooling, leading to thermal contraction
and internal phase changes; or tidal despinning, leading to collapse of an equatorial bulge; or a combination of
both. It has been further suggested that the orientations of lobate scarps could reflect a pattern of mantle convection.
Here we review compressional tectonics localized along the interface between basin-fill and the inner walls of
>200 km diameter mercurian impact basins. This occurs as outward-directed thrust faults following the inside
of basin rims, and sometimes completely over-thrusting the rim location. Thrusting at the edges of low-latitude
basins tends to be most strongly developed at eastern and western rims, suggesting tidal despinning as a driving
force. Cross-cutting relationships show examples of thrusting that must considerably post-date the volcanic infilling
of the associated basin, suggesting despinning occurring (or continuing) well after the end of the late heavy
bombardment, contrary to previous expectation
A SPECTRUM OF TECTONISED BASIN EDGES ON MERCURY.
No full textLobate scarps on Mercury are generally accepted as being surface expressions of thrust faulting. This is taken as evidence of litho-spheric contraction on a global scale, reflecting either global cooling, leading to thermal contraction and internal phase changes; or tidal despinning, leading to collapse of an equatorial bulge; or a combination of both. It has been further suggested that the orientations of lobate scarps could reflect a pattern of mantle convection.
Here we describe compressional tectonics local-ized along the interface between basin-fill and the inner walls of >200 km diameter impact basins. These are considerably larger than the ghost craters with deformed rims that have been the focus of other stud-ies . We draw attention to several ex-amples of outward-directed thrust faults following the inside of basin rims, mostly un-remarked in a global survey of >300 km basins by Fassett et al. 201
Evolution of a poly-deformed relay zone between fault segments in the eastern Southern Alps, Italy.
Full text linkIn the eastern Southern Alps (NE Italy), Liassic north–south extensional structures are prominent. The southern Trento Platform also experienced extension during the Palaeogene, when reactivation of some pre-existing faults occurred, coupled with nucleation of new faults. During Neogene shortening, these structures were reactivated once again, but with strike-slip kinematics.
In this framework, the Gamonda–Tormeno restraining stepover represents the final result of an overlap zone which evolved through time. In the first stage (Lias to Early Cretaceous) a prominent splay developed at the tip of the Gamonda Fault by lateral propagation and breaching of independent segments. At the same time, there was kinematic interaction between the antithetic Gamonda
and Tormeno faults, followed by diachronous motion on crossing faults and the development of a narrow graben. During the second stage of extensional tectonics (Palaeocene to Early Oligocene), the reactivation and propagation of the overlapping faults along with the generation of new faults
led to deepening of the graben. In the third stage (Miocene to present), the final structure of a strike-slip restraining stepover was accomplished. Due to the mechanical stratigraphy and complex inherited architecture of the relay zone where stratigraphic sequences with different rheological properties are juxtaposed, the style of shortening is different in the western and eastern sides of the stepover. The Gamonda–Tormeno structure represents a unique example of how a relay zone may change through time
Are plumes on motionless plates analogues to Martian plume feeding the giant shield volcanoes?
Full text linkThe near “one-plate” planet evolution of Mars has led to the
edification of long-lasting giant shied volcanoes, which dominate the topography of its western hemisphere. Unlike the Earth, Mars would have been a transient convecting planet, where plate tectonic would have possibly acted only during the first hundreds of million years of its history. Most of the Martian magmatic activity would be very old (Noachian) and has been preserved compared to the Earth in the near-absence of crustal recycling. Recent volcanic resurgence occurred in the two main Martian volcanic provinces, so-called Tharsis and Elysium. Although the large igneous magmatic provinces of Mars bear some geomorphological similarities with terrestrial oceanic plateaus, they distinguish themself by their larger scale-size. Their accretion, which is vertical due to the absence of lateral plate movement and crustal recycling, loads the lithosphere and causes lithospheric flexure, deformation and edifice flank failure. Underlying these huge volcanoes, the lithosphere might reach a thickness up to 150 km. The thickening of the lithospheric lid over time will have increased the final melting depth and thereby reduced the mean melting degree. Such kind of lithospheric processes are commonly observed in near stationary plate plume settings. However, while the Hawaiian Islands are located on a fast-moving plate (i.e. pacific, 7-8 cm/yr), Hawaiian hotspot intraplate magmatic activity has been commonly considered as some of the best analogs to that of observed on Mars. However, intraplate oceanic volcanism at slow moving plates such as Crozet
or Cape Verde islands might constitute a better analog. As on
Mars, volcanoes at motionless plates do not show any linear age progression, but constitute the sites of persistent, long-term magmatic activity. Because the lithosphere lid is near stagnant in these areas, the melting mantle region concentrates its products in a single area, rather than having them spread out as observed in fast-moving plate plume environment such as the Hawaiian-Emperor chain. The melt products accrete vertically into huge accumulation, generating oceanic swell heights unusually shallow for their ages. The loading of the lithosphere by the volcanic accumulations may cause flexural deformation and/or edifice collapse. These processes are likely similar to those observed on Mars. The goal of this presentation will be to describe the essential characteristics of intra-oceanic plumes on slow moving
plates on the Earth and compare them to large shield volcanoes from the Tharsis region
Association of cone sheets and radial dykes on Ascraeus Mons (Mars): structural analysis and modelling
No full textAscraeus Mons was one of the first of the Martian volcanoes to be imaged by the High Resolution Stereo Camera
(HRSC) experiment onboard the ESA Mars Express spacecraft. These images show much of the volcano at a
higher resolution than previously (12 m/px), and details of its lava flows, sinuous rilles, flank vents and tectonic
features. Concentric fractures systems (pit chains, grabens) around the volcano, changing transitionally into radial
structures systems have been recognized and cartographed using a HRSC mosaic. The structural interpretation
showed strong analogies with concentric dykes (cone sheets) on many terrestrial volcanoes such as Isla Fernandina
(Galapagos), Tejeda Complex (Canary Islands) and Cuillins Complex (Isle of Skye, Scotland). In particular this
last terrestrial analogue has been studied in detail and with the use of a Finite Element Method (FEM) modeling the
shape of the magma chamber that originated the cone sheets on the Cuillins Complex was discovered (Bistacchi
et al. 2010). An oblate inflating magma chamber is responsible for the formation of those structures. By analogy,
we tested the presence of an oblate magma chamber below Ascraeus Mons. We measured the diameter of the
transition zone between concentric and radial structures on Ascraeus Mons flanks, that is strongly related to the
diameter of the deep magma chamber (1-1.2 magma chamber diameters). With a FEM model built for Ascraeus
we have been able to discover the average depth of the oblate magma chamber, which could have originated the
concentric structures. The presence of a plume with an oblate summit instead of the magma chamber has also
been tested. Moreover an additional oblate shallow magma chamber that likely originated the summit caldera has
been verified. In addition, the deformation event that originated the structures on Ascraeus flanks has been dated
by crater counting, resulting very recent
Post-nappe brittle tectonics and kinematic evolution of the north-western Alps: an integrated approach
No full textData from remote sensing, structural geology and thermochronology provide the basis for this integrated reconstruction of the Oligocene to Present kinematic evolution of the north-western Alpine nappe stack. Two brittle tectonic phases post-date the Cretaceous–Eocene ductile deformation. A NW–SE extension developed in the Oligocene (D1) along three main conjugate fault systems arranged in orthorhombic symmetry (N-, NW- and SE-dipping). Cooling rate contour maps, from published apatite and zircon fission-track ages and Rb/Sr biotite ages, highlight the differential exhumation of large fault-bounded blocks during this phase, whilst synkinematic hydrothermal veins and calc-alkaline dykes (29–32 Ma) help to constrain its age. From the Miocene onwards, a general rearrangement of the strain pattern led to SW-directed lateral extrusion (D2) of the Pennine-Graian Alps block, bounded by a network of seismogenic shear zones, the most important being the Ospizio Sottile, Simplon, Rhone and Chamonix faults. The internal deformation of the Pennine-Graian Alps block is characterised by an overall more or less homogeneous NE–SW extension. The approach undertaken, integrating remote sensing, structural analysis on different scales, and thermochronology (with the cooling rate map representation), is therefore effective in reconstructing the late-orogenic extensional tectonic evolution of metamorphic nappe stacks
Tumuli vs Pingos: A comparative study between Daedalia Planum and Elysium Planitia features
No full textAre magmatic processes at volcanoes from motionless plates analogues to those of the giant shield volcanoes on Mars?
Full text linkThe near “one-plate” planet evolution of Mars has led to the edification of long-lasting giant shied volcanoes. Unlike the Earth, Mars would have been a transient convecting planet, where plate tectonic would have possibly acted only during the first hundreds of million years of its history. On Earth, where plate tectonic is active, most plates are regenerated and recycled through convection. However, the Nubian and Antarctic plates could be considered as poorly mobile surfaces of various thicknesses that are acting as conductive lids on top of Earth’s deeper convective system. In these environments, volcanoes do not show any linear age progression at least for the last 30 Ma, but constitute the sites of persistent, spatially
focused long-lived magmatic activity. Here, the near stationary absolute plate motion probably exerts a primary control on volcanic processes, and more specifically, on the melting ones. Depleted mantle residues left behind by the melting processes are difficultly dragged away from the melting locus. The thickening of the near-stationary depleted layer progressively forces the termination of melting to higher depths, reducing
melt production rate, extraction and increasing mantle lithospheric-melt interactions. With time, it might cause long term fluctuations of the volcanic activity, in generating long periods of quiescence. The pronounced topographic swells/bulges observed in these environments are thus probably both supported by large scale mantle upwelling and residual mantle roots. Most of these processes are likely similar to those observed on Martian giant shield volcanoes. The goal of this presentation will be to describe the essential characteristics of intra-oceanic magmatic processes on slow
moving plates on the Earth and to point out their similarities with those of the large shield volcanoes from the Tharsis region
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Beagle Rupes - Evidence for a basal decollement of regional extent in Mercury's lithosphere
Full text linkThanks to its location at low latitude and close to the terminator in the outbound view of Mercury obtained during MESSENGER’s first fly-by, the Beagle Rupes lobate scarp on Mercury has been particularly clearly imaged. This enables us to interpret it as a component of a linked fault system, consisting of a frontal scarp terminated by transpressive lateral ramps. The terrain bounded by these surface manifestations of faulting is the hanging-wall block of a thrust sheet and must be underlain by a basal decollement (a detachment horizon) constituting the fault zone at depth. The decollement must extend a minimum of 150 km eastwards from the frontal scarp, and at least 400 km if displacement is transferred to features interpreted as out-of-sequence thrusts and offset lateral ramps that appear to continue the linked fault system to the east. The depth of the basal decollement could be controlled by crustal stratigraphy
or by rheological change within, or at the base of, the lithosphere. Previous interpretations of mercurian lobate scarps regard their thrusts as uniformly dipping and dying out at depth, lacking lateral ramps and any extensive detachment horizon. Anticipated improvements in image resolution and lighting geometry should make it possible to document what percentage of lobate scarps share the Beagle Rupes style of tectonics
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