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Although Earth is the only known planet on which plate tectonics operates, many small- and large-scale tectonic landforms indicate that deformational processes also occur on the other rocky planets. Although the mechanisms of deformation differ on Mercury, Venus, and Mars, the surface manifestations of their tectonics are frequently very similar to those found on Earth. Furthermore, tectonic processes invoked to explain deformation on Earth before the recognition of horizontal mobility of tectonic plates remain relevant for the other rocky planets. These connections highlight the importance of drawing analogies between the rocky planets for characterizing deformation of their lithospheres and for describing, applying appropriate nomenclature, and understanding the formation of their resulting tectonic structures. Here we characterize and compare the lithospheres of the rocky planets, describe structures of interest and where we study them, provide examples of how historic views on geology are applicable to planetary tectonics, and then apply these concepts to Mercury, Venus, and Mars. Key words: planetary tectonics, planetary geology, Mercury, Venus, Mars. Bien que la Terre soit la seule planete connue sur laquelle il y a une tectonique des plaques, de nombreuses formes de relief tectoniques de petite et grande envergure indiquent que des processus de deformation se produisent egalement sur d'autres planetes rocheuses. Si les mecanismes de deformation sur Mercure, Venus et Mars different, les manifestations en surface de leurs tectoniques respectives sont souvent tres semblables a celles observees sur la Terre. En outre, des processus tectoniques invoques pour expliquer la deformation sur la Terre avant la reconnaissance de la mobilite horizontale de plaques tectoniques revetent toujours une pertinence pour les autres planetes rocheuses. Ces connexions soulignent l'importance d'etablir des analogies entre les planetes rocheuses pour caracteriser la deformation de leurs lithospheres et pour decrire, en appliquant la bonne nomenclature, et comprendre la formation des structures tectoniques en resultant. Nous caracterisons et comparons les lithospheres des planetes rocheuses, decrivons les structures d'interet et les lieux ou elles sont etudiees, et presentons des exemples d'application de notions historiques a la tectonique planetaire pour ensuite appliquer ces concepts a Mercure, Venus et Mars. [Traduit par la Redaction] Mots-cles: tectonique des planetes, geologie des planetes, Mercure, Venus, Mars., Introduction Without a theoretical framework, such as the plate tectonic models, of the spatial relations of rock bodies to one another in an orogenic belt, however wrong they may be, [...]

Surface geologic features form a detailed record of Venus' evolution. Venus displays a profusion of volcanic and tectonics features, including both familiar and exotic forms. One challenge to assessing the role of these features in Venus' evolution is that there are too few impact craters to permit age dates for specific features or regions. Similarly, without surface water, erosion is limited and cannot be used to evaluate age. These same observations indicate Venus has, on average, a very young surface (150–1000 Ma), with the most recent surface deformation and volcanism largely preserved on the surface except where covered by limited impact ejecta. In contrast, most geologic activity on Mars, the Moon, and Mercury occurred in the 1st billion years. Earth's geologic processes are almost all a result of plate tectonics. Venus' lacks such a network of connected, large scale plates, leaving the nature of Venus' dominant geodynamic process up for debate. In this review article, we describe Venus' key volcanic and tectonic features, models for their origin, and possible links to evolution. We also present current knowledge of the composition and thickness of the crust, lithospheric thickness, and heat flow given their critical role in shaping surface geology and interior evolution. Given Venus' hot lithosphere, abundant activity and potential analogues of continents, roll-back subduction, and microplates, it may provide insights into early Earth, prior to the onset of true plate tectonics. We explore similarities and differences between Venus and the Proterozoic or Archean Earth. Finally, we describe the future measurements needed to advance our understanding of volcanism, tectonism, and the evolution of Venus. [ABSTRACT FROM AUTHOR]

The dynamics and evolution of Venus' mantle are of first-order relevance for the origin and modification of the tectonic and volcanic structures we observe on Venus today. Solid-state convection in the mantle induces stresses into the lithosphere and crust that drive deformation leading to tectonic signatures. Thermal coupling of the mantle with the atmosphere and the core leads to a distinct structure with substantial lateral heterogeneity, thermally and compositionally. These processes ultimately shape Venus' tectonic regime and provide the framework to interpret surface observations made on Venus, such as gravity and topography. Tectonic and convective processes are continuously changing through geological time, largely driven by the long-term thermal and compositional evolution of Venus' mantle. To date, no consensus has been reached on the geodynamic regime Venus' mantle is presently in, mostly because observational data remains fragmentary. In contrast to Earth, Venus' mantle does not support the existence of continuous plate tectonics on its surface. However, the planet's surface signature substantially deviates from those of tectonically largely inactive bodies, such as Mars, Mercury, or the Moon. This work reviews the current state of knowledge of Venus' mantle dynamics and evolution through time, focussing on a dynamic system perspective. Available observations to constrain the deep interior are evaluated and their insufficiency to pin down Venus' evolutionary path is emphasised. Future missions will likely revive the discussion of these open issues and boost our current understanding by filling current data gaps; some promising avenues are discussed in this chapter. [ABSTRACT FROM AUTHOR]

Noctis Labyrinthus is a little‐studied and structurally complex area situated between the Tharsis Rise and Valles Marineris on Mars. Noctis Labyrinthus is dissected by normal faults that form horst and graben, pit craters situated inside the graben, and large troughs that cross‐cut both graben and pit craters. Mass wasting, periglacial, and some erosive fluvial features are observed at the bases of the troughs, suggesting that the troughs hosted liquid and perhaps even ice at some point in the past. We mapped and analyzed these structural and morphological features in Noctis Labyrinthus to establish the region's formational history. Fault throw profiles, combined with morphometric data from pit craters, were used to assess how the pit craters relate to the much larger troughs in the region and whether those troughs were formed by extensional tectonic deformation alone. This comparative analysis suggests that some pit craters grew deeper than the amount of throw accommodated by their bounding faults. We hypothesize that layers with subsurface volatiles (such as ground ice) were intersected and exposed by the larger Noctis Labyrinthus pit craters, enabling sublimation that further promoted mass wasting and the growth and coalescence of pits and graben into the large troughs. Under this scenario, subsurface volatiles played an important role in forming this structurally complex region, and may still be present there. Plain Language Summary: Noctis Labyrinthus (Lat., "Labyrinth of the Night") on Mars is a topographically complex region situated between Mars' largest volcanic province, Tharsis, and the vast canyon system, Valles Marineris. The Noctis Labyrinthus region has many fractures, pits, craters, and troughs, but how these features formed and interacted with one another is still not fully understood. We mapped the fractures, pits, craters, and troughs in this region to better understand the relative timing of the formation of Noctis Labyrinthus. We conclude that extension of the crust led to pit crater formation through the drainage of surface material into fractures. Further dissection of the landscape was enhanced by the exposure of ice in the subsurface during pit formation that was then melted or sublimated to create ever‐larger depressions. We estimated the depth of this subsurface ice from the distribution and sizes of craters with fluidized ejecta deposits. The bottoms and walls of the troughs show physical evidence for a long‐term role played by ice in the formation of this distinctive part of Mars. Key Points: Noctis Labyrinthus is host to more than 200 pit craters, over 100 deep troughs, and thousands of normal faultsEvidence of erosional processes is present in the form of mass wasting and periglacial landforms located in the deep troughsThe formation of Noctis Labyrinthus was enhanced through substantial volatile loss, as recorded by the periglacial features in the troughs [ABSTRACT FROM AUTHOR]

Venus has been thought to possess a globally continuous lithosphere, in contrast to the mosaic of mobile tectonic plates that characterizes Earth. However, the Venus surface has been extensively deformed, and convection of the underlying mantle, possibly acting in concert with a low-strength lower crust, has been suggested as a source of some surface horizontal strains. The extent of surface mobility on Venus driven by mantle convection, however, and the style and scale of its tectonic expression have been unclear. We report a globally distributed set of crustal blocks in the Venus lowlands that show evidence for having rotated and/or moved laterally relative to one another, akin to jostling pack ice. At least some of this deformation on Venus postdates the emplacement of the locally youngest plains materials. Lithospheric stresses calculated from interior viscous flow models consistent with long-wavelength gravity and topography are sufficient to drive brittle failure in the upper Venus crust in all areas where these blocks are present, confirming that interior convective motion can provide a mechanism for driving deformation at the surface. The limited but widespread lithospheric mobility of Venus, in marked contrast to the tectonic styles indicative of a static lithosphere on Mercury, the Moon, and Mars, may offer parallels to interior-surface coupling on the early Earth, when global heat flux was substantially higher, and the lithosphere generally thinner, than today. [ABSTRACT FROM AUTHOR]

Shortening tectonic structures within Mercury's two largest geological units display a clear contrast in relief, length, and spatial density. The volcanic smooth plains units are deformed by smaller‐scale structures yet host more features per area than the older intercrater plains. Although faulting in the intercrater plains is dominantly attributed to global contraction, it has been unclear whether the smooth plains faults result from volcanic loading, global contraction, or both. We use estimates of fault length and displacement to calculate spatial variations of areal strain for each unit. We find that high strain concentrations within the smooth plains suggest that global contraction has contributed to deformation in these units. The observed contrast in morphology and spatial density of structures between units may primarily reflect differences in mechanical and/or structural characteristics of the lithosphere when faulting was initiated. Plain Language Summary: Slow cooling of Mercury's mantle and core has decreased the radius of the planet by as much as 7 km. This radial contraction put the crust in a state of horizontal compression resulting in widespread thrust faulting. Extensive flood volcanism resurfaced portions of the crust, the most recent deposits of which are termed producing the smooth plains. Thrust faults are also observed within these plains, but it is not clear whether these features formed from global contraction or from bending of the crust due to the weight of the emplaced lavas. In this study, we measure the length of the faults and their relief (height) to calculate the spatial distribution of strain (horizontal shortening) in both the smooth plains and intercrater plains of Mercury. We find that the amount of strain recorded in the smooth plains is best explained by at least some contribution from stresses due to global contraction. Therefore, we suggest that all geological units on Mercury have been deformed by global contraction, indicating that substantial radius decrease occurred after the bulk of volcanic activity had ended. Key Points: We measure the relief of 672 and 584 shortening structures in Mercury's smooth plains and intercrater plains units, respectivelyAreal strain estimates for the smooth plains and intercrater plains are similar, suggesting both units record similar amounts of shortening strain from global contractionDifferences in morphology and fault density of shortening structures may reflect differences in lithospheric structure at fault initiation [ABSTRACT FROM AUTHOR]

Abstract We propose a global framework for the Earth system to facilitate communication between the geoscience community, the public and policy makers. Geoscience research aims to understand the history and evolution of the Earth system. This combines the non-living and living parts of the Earth, especially through interactions of the lithosphere, biosphere and atmosphere as well as the other parts of the system, such as the asthenosphere, core and extraterrestrial influences. Such research considers a system that spans scales from microscopic (micrometer scale) to megascopic (many 1000 s of km scale), and from milliseconds to millions of years. To connect different parts of this immense system, we habitually use a wide range of ad hoc geological frameworks, systems and geological environment models, where different processes and features operate and combine. In consequence, one way to judge the significance of our work, and to increase its value, is to assess how the elements studied are integrated within the whole Earth system. This allows us to see what implications any study has for this greater Earth system. To do this successfully, our research needs a standard global framework to assess a study's relevance. However, such a global framework does not formally exist, and so this article looks at existing examples and proposes one that can systematically place research into a global geological context. This proposed framework has the advantage of being useful for communicating geological processes to other disciplines, and can be used for any type of Earth (or planetary) environment. This framework is a fundamental tool for geoscience communication and for outreach, especially through geological heritage (geoheritage). Geoheritage concerns the valuing and protection of geoscience and geological sites, and is a vital tool for communicating geoscience. It can be used to communicate our knowledge of global change, providing, through landscapes and outcrops, a story that renders the concepts and advances of geoscience accessible. Like our basic research, the concept of geoheritage evolves as our understanding of the Earth progresses, and these dual changes can be explained with the global framework. Geoheritage is a global activity and it needs a global framework to put sites into context. A revision of the UNESCO geological thematic studies was called for by the World Heritage Committee in 2014 (decision: 38 COM 8B.11), and this can be done with the input from the full geoscience community using this global geological framework. Thus, for research, geoscience policy and for geoheritage, a global framework is now needed. The proposed framework can place any site in its geological environment, related to its lithospheric plate tectonic setting and its history. The framework has a solid-earth bias (lithosphere), but includes all other spheres, such as the biosphere and anthropogenic activity. Extraterrestrial influences, like solar variations and metorite impacts are included. The framework is phenomenological, due to the necessity of grouping the features that we see, but these phenomena provide evidence of processes that we cannot see. The basic format is a table, a sketch of the Earth and a system diagram, three complementary and most powerful ways of depicting a system. A timeline, or stratigraphic column can be included, to show the evolution of geological history, and the table can be used as a 'game board' where one site migrates across from one set of conditions to another over time. The global framework allows any research site, area or subject to be set in the Earth's system, in a way that gives it context, allows comparisons and provides significance. We suggest that it can be a template for an internationally accepted version used to consolidate the necessary geoscience – geoheritage link and promote outreach. Highlights • Comprehensive Global Geological Framework • The Earth system in one diagram: putting the geology in context • Allows Earth science concepts to be communicated and understood to a broad audience. [ABSTRACT FROM AUTHOR]

Mercury's global tectonic history is thought to have been dominated by two major processes: tidal despinning and global contraction. Each process is expected to have produced a distinctive global stress field and resultant fault pattern. Thousands of thrust-fault-related landforms documented on Mercury can be attributed to global contraction, but no global signature of tidal despinning has been conclusively documented. Because global contraction operated throughout an extended portion of Mercury's geologic history, any tidal despinning pattern either would have formed together with global contraction, or would have been modified by global contraction after despinning was complete. Here, we reassess global fracture patterns predicted to result from tidal despinning and from a combination of tidal despinning and global contraction. We specifically make use of rock strength and deformability parameters appropriate for Mercury's fractured lithosphere. Results indicate that a tidal despinning pattern would consist only of a global set of opening-mode fractures (joints) in the upper part of the lithosphere, whereas the combination of tidal despinning and global contraction would have produced a global population of thrust faults, with no preferred orientations in the polar regions but with an increasing preference for north–south orientations toward the equator. If an equatorial bulge from an early state of rapid spin was supported by Mercury's lithosphere, two end-member scenarios for the timing and duration of these two processes may be considered. In one, tidal despinning predated global contraction; in the other, tidal despinning and global contraction overlapped in time. We test the predictions of both scenarios against the distribution and orientations of Mercury's tectonic landforms. The global pattern of thrust faults is generally consistent with predictions for the scenario under which tidal despinning and global contraction temporally overlapped. [ABSTRACT FROM AUTHOR]

Mercury, a planet with a lithosphere that forms a single tectonic plate, is replete with tectonic structures interpreted to be the result of planetary cooling and contraction. However, the amount of global contraction inferred from spacecraft images has been far lower than that predicted by models of the thermal evolution of the planet's interior. Here we present a synthesis of the global contraction of Mercury from orbital observations acquired by the MESSENGER spacecraft. We show that Mercury's global contraction has been accommodated by a substantially greater number and variety of structures than previously recognized, including long belts of ridges and scarps where the crust has been folded and faulted. The tectonic features on Mercury are consistent with models for large-scale deformation proposed for a globally contracting Earth-now obsolete-that pre-date plate tectonics theory. We find that Mercury has contracted radially by as much as 7 km, well in excess of the 0.8-3 km previously reported from photogeology and resolving the discrepancy with thermal models. Our findings provide a key constraint for studies of Mercury's thermal history, bulk silicate abundances of heat-producing elements, mantle convection and the structure of its large metallic core. [ABSTRACT FROM AUTHOR]

Highlights • Most pyroclastic vents on Mercury are located near impact craters and faults. • The occurrence of vents near faults is statistically indistinguishable from random. • The occurrence of vents in impact craters is statistically resolvable from random. • Larger pyroclastic eruptions occurred in more highly fractured areas. Abstract Mercury's surface preserves a rich history of volcanism, impact cratering, and tectonic deformation. Geological observations show that the earliest evidence of thrust faulting that was induced by the secular cooling and resulting global contraction of the planet coincided with the waning stages of effusive volcanism, but that explosive volcanism continued beyond this point. Stresses from global contraction, however, would have precluded efficient vertical magma ascent. Sites of pyroclastic activity—manifest as irregular depressions surrounded by diffuse, spectrally distinct halos—spatially coincide with lithospheric discontinuities, such as faults or those associated with impact craters. The vast majority of explosive vents are situated on the floors, rims, central peaks, or peak rings of impact structures. A substantial portion of such vents is also proximal to thrust faults: they are most spatially concentrated at or within 20 km of faults, with ever fewer vents progressively farther from tectonic structures. We statistically evaluated the spatial distribution of sites of pyroclastic activity with respect to faults and impact craters by generating sets of random point locations of equal count to those volcanic sites, computing their spatial relationship to the mapped faults and craters, and comparing them to our observations. We find that although the observed proximity of vents to faults is indistinguishable from a random distribution, their spatial association with impact craters is non-random. To examine the interrelatedness of several geospatial relationships of lithospheric weaknesses and pyroclastic activity, we performed a principal component analysis that tested correlations between vent size, the presence of vents within a crater, the diameters and degradation states of those craters, and vent distance from mapped faults, which help tie together interpretations of magma volumes and eruption energies, repeated utilization of magma pathways, and durations of eruptive events in the geological context of global contraction. Results reveal a predominance of small-sized vents indicative of short-lived, low-volume pyroclastic activity that are consistent with suppressed volcanism after the onset of global contraction. Greater size ranges of vents are found in large impact craters and when faults are nearby, which points to denser fracture networks facilitating magma ascent. [ABSTRACT FROM AUTHOR]

Venus differs from the Earth with its single plate geodynamic regime compared with the subduction dominated Earth's plate tectonics. Therefore, the tectonic-magmatic processes in Venus are controlled by vertical forcing. Upwelling and downwelling processes cause various geological structures (Coronae, Nova, Arachnoid) due to the high surface temperature, low water content and high atmospheric pressure on Venus. More specifically, Coronae are formed on hotspots, around major rift zones and isolated fractures in plains throughout the Venus. Nevertheless, it is not well understood how Type-1 (symmetric) and Type-2 (asymmetric) coronae are formed in relation to mantle dynamics. We use numerical geodynamic experiments to investigate the effects of lithospheric downwellings-upwellings as well as related dynamic topography on the corona formation sequence. To initiate the instability, we insert an eclogitic/dense body (50 km x 200 km) on the lower crust. In the models, varying crustal and lithospheric rheologies, and densities are tested as a parameterized work. Our model results yielded three different rheological lithospheric behaviors; (i) stable (no instability), (ii) mantle lithosphere involved instabilities and (iii) pierce through of the dense body in the mantle lithospheric domain. Overall, our topography results are consistent with the coronae types that are classified by their topographic shapes. Future studies will try to explain the existence of the asymmetrically shaped coronae, in the presence of a rheologically weak lower crust, which is proposed to be the reason of decoupling process. [ABSTRACT FROM AUTHOR]