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Tectonics of Mars
Tectonics of Mars
Tectonics of Mars
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Topographic map of Mars showing the highland-lowland boundary marked in yellow, and the Tharsis rise outlined in red (USGS, 2014).[1]

Like the Earth, the crustal properties and structure of the surface of Mars are thought to have evolved through time; in other words, as on Earth, tectonic processes have shaped the planet. However, both the ways this change has happened and the properties of the planet's lithosphere are very different when compared to the Earth. Today, Mars is believed to be largely tectonically inactive. However, observational evidence and its interpretation suggests that this was not the case further back in Mars's geological history.

At the scale of the whole planet, two large scale physiographic features are apparent on the surface. The first is that the northern hemisphere of the planet is much lower than the southern, and has been more recently resurfaced – also implying that the crustal thickness beneath the surface is distinctly bimodal. This feature is referred to as the "hemispheric dichotomy". The second is the Tharsis rise, a massive volcanic province that has had major tectonic influences both on a regional and global scale in Mars's past. On this basis, the surface of Mars is often divided into three major physiographic provinces, each with different geological and tectonic characteristics: the northern plains, the southern highlands, and the Tharsis plateau. Much tectonic study of Mars seeks to explain the processes that led to the planet's division into these three provinces, and how their differing characteristics arose. Hypotheses proposed to explain how the two primary tectonic events may have occurred are usually divided into endogenic (arising from the planet itself) and exogenic (foreign to the planet, e.g., meteorite impact) processes.[2] This distinction occurs throughout the study of tectonics on Mars.

In general, Mars lacks unambiguous evidence that terrestrial-style plate tectonics has shaped its surface.[3] However, in some places magnetic anomalies in the Martian crust that are linear in shape and of alternating polarity have been detected by orbiting satellites. Some authors have argued that these share an origin with similar stripes found on Earth's seafloor, which have been attributed to gradual production of new crust at spreading mid-ocean ridges.[4] Other authors have argued that large-scale strike-slip fault zones can be identified on the surface of Mars (e.g., in the Valles Marineris trough), which can be likened to plate-bounding transform faults on Earth such as the San Andreas and Dead Sea faults. These observations provide some indication that at least some parts of Mars may have undergone plate tectonics deep in its geological past.[5]

Physiographic provinces

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Southern highlands

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The southern highlands are heavily cratered and separated from the northern plains by the global dichotomy boundary.[4] Strong magnetic stripes with alternating polarity run roughly east to west in the southern hemisphere, concentric with the south pole.[6] These magnetic anomalies are found in rocks dating from the first 500 million years in Mars's history, indicating that an intrinsic magnetic field would have ceased to exist before the early Noachian. The magnetic anomalies on Mars measure 200 km width, roughly ten times wider than those found on Earth.[6]

Northern plains

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The northern plains are several kilometers lower in elevation than the southern highlands, and have a much lower crater density, indicating a younger surface age. The underlying crust is however thought to be the same age as that of the southern highlands. Unlike the southern highlands, magnetic anomalies in the northern plains are sparse and weak.[2]

Tharsis plateau

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Geological map of the region around the Tharsis plateau. Extensional and compressional features – e.g., graben and wrinkle ridges – have been mapped and are visible in the image. (USGS, 2014).[1]

The Tharsis plateau, which sits in the highland-lowland boundary, is an elevated region that covers roughly one quarter of the planet. Tharsis is topped by the largest shield volcanoes known in the Solar System. Olympus Mons stands 24 km tall and is nearly 600 km in diameter. The adjoining Tharsis Montes consists of Ascraeus, Pavonis, and Arsia. Alba Mons, at the northern end of the Tharsis plateau, is 1500 km in diameter, and stands 6 km above the surrounding plains. In comparison, Mauna Loa is merely 120 km wide but stands 9 km above the sea floor.[4]

The load of Tharsis has had both regional and global influences.[2] Extensional features radiating from Tharsis include graben several kilometers wide, and hundreds of meters deep, as well as enormous troughs and rifts up to 600 km wide and several kilometers deep. These graben and rifts are bounded by steeply dipping normal faults, and can extend for distances up to 4000 km. Their relief indicates that they accommodate small amounts of extension on the order of 100 m or less. It has been argued that these graben are surface expressions of deflated subsurface dikes.[7]

Circumferential to Tharsis are so-called wrinkle ridges.[2] These are compressional structures composed of linear asymmetric ridges that can be tens of kilometers wide and hundreds of kilometers long. Many aspects of these ridges appear to be consistent with terrestrial compressional features that involve surface folding overlying blind thrust faults at depth.[8] Wrinkle ridges are believed to accommodate small amounts of shortening on the order of 100 m or less. Larger ridges and scarps have also been identified on Mars. These features can be several kilometers high (as opposed to hundreds of meters high for wrinkle ridges), and are thought to represent large lithosphere-scale thrust faults.[9] Displacement ratios for these are ten times those of wrinkle ridges, with shortening estimated to be hundreds of meters to kilometers.

Approximately half of the extensional features on Mars formed during the Noachian, and have changed very little since, indicating that tectonic activity peaked early on and decreased with time. Wrinkle ridge formation both around Tharsis and in the eastern hemisphere is thought to have peaked in the Hesperian, likely due to global contraction attributed to cooling of the planet.[2]

Hemispheric dichotomy

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Main article: Martian dichotomy

Hypsometry

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Histogram of crustal thickness versus area on Mars, adapted from Neumann et al., 2004. The hemispheric dichotomy is clear in the two peaks in the data.[10]

Gravity and topography data show that crustal thickness on Mars is resolved into two major peaks, with modal thicknesses of 32 km and 58 km in the northern and southern hemispheres, respectively.[10] Regionally, the thickest crust is associated with the Tharsis plateau, where crustal thickness in some areas exceeds 80 km, and the thinnest crust with impact basins. The major impact basins collectively make up a small histogram peak from 5 to 20 km.

The origin of the hemispheric dichotomy, which separates the northern plains from the southern highlands, has been subject to much debate. Important observations to take into account when considering its origin include the following: (1) The northern plains and southern highlands have distinct thicknesses, (2) the crust underlying the northern plains is essentially the same age as the crust of the southern highlands, and (3) the northern plains, unlike the southern highlands, contain sparse and weak magnetic anomalies. As will be discussed below, hypotheses for the formation of the dichotomy can largely be divided into endogenic and exogenic processes.[2]

Endogenic origins

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A possible plate tectonic explanation for the northern lowlands. The Boreal plate is shown in yellow. Trenches are shown by toothed lines, ridges by double lines, and transform faults by single lines, modified from Sleep, 1994.[11]

Endogenic hypotheses include the possibility of a very early plate tectonic phase on Mars.[11] Such a scenario suggests that the northern hemispheric crust is a relic oceanic plate. In the preferred reconstruction, a spreading center extended north of Terra Cimmeria between Daedalia Planum and Isidis Planitia. As spreading progressed, the Boreal plate broke into the Acidalia plate with south-dipping subducting beneath Arabia Terra, and the Ulysses plate with east-dipping subducting beneath Tempe Terra and Tharsis Montes. According to this reconstruction, the northern plains would have been generated by a single spreading ridge, with Tharsis Montes qualifying as an island arc.[4] However, subsequent investigations of this model show a general lack of evidence for tectonism and volcanism in areas where such activity was initially predicted.[12]

Another endogenic process used to explain the hemispheric dichotomy is that of primary crustal fractionation.[13] This process would have been associated with the formation of the Martian core, which took place immediately after planetary accretion. Nevertheless, such an early origin of the hemispheric dichotomy is challenged by the fact that only minor magnetic anomalies have been detected in the northern plains.[2]

A model for a mantle plume origin for the hemispheric dichotomy. Single plume mantle convection generates new crust in southern hemisphere with alternating bands of normal and reversed remanent magnetism, adapted from Vita-Finzi & Fortes, 2013.[4]

Single plume mantle convection has also been invoked to explain the hemispheric dichotomy. This process would have caused substantial melting and crustal production above a single rising mantle plume in the southern hemisphere, resulting in a thickened crust. It has also been suggested that the formation of a highly viscous melt layer beneath the thickened crust in the southern hemisphere could lead to lithospheric rotation. This may have resulted in the migration of volcanically active areas toward the dichotomy boundary, and the subsequent placement and formation of the Tharsis plateau. The single plume hypothesis is also used to explain the presence of magnetic anomalies in the southern hemisphere, and the lack thereof in the northern hemisphere.[14]

Exogenic origins

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Exogenic hypotheses involve one or more large impacts as being responsible for the lowering of the northern plains. Although a multiple-impact origin has been proposed,[15] it would have required an improbable preferential bombardment of the northern hemisphere.[2] It is also unlikely that multiple impacts would have been able to strip ejecta from the northern hemisphere, and uniformly strip the crust to a relatively consistent depth of 3 km.

Mapping of the northern plains and the dichotomy boundary shows that the crustal dichotomy is elliptical in shape.[16] This suggests that formation of the northern plains was caused by a single oblique mega-impact. This hypothesis is in agreement with numerical models of impacts in the 30-60° range, which are shown to produce elliptical boundary basins similar to the structure identified on Mars.[2] Demagnetization resulting from the high heat associated with such an impact can also serve to explain the apparent lack of magnetic anomalies in the northern plains. It also explains the younger surface age of the northern plains, as determined by significantly lesser crater density. Overall, this hypothesis appears to fare better than others that have been proposed.

Tectonic implications of magnetic anomalies

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Map of crustal magnetic anomaly distribution on Mars, courtesy of NASA, 2005.

The southern highlands of Mars display zones of intense crustal magnetization. The magnetic anomalies are weak or absent in the vicinity of large impact basins, the northern plains, and in volcanic regions, indicating that magnetization in these areas have been erased by thermal events. The presence of magnetic anomalies on Mars suggests that the planet maintained an intrinsic magnetic field early on in its history.[2] The anomalies are linear in shape and of alternating polarity, which some authors have interpreted as a sequence of reversals and a process akin to seafloor spreading.[4] The stripes are ten times wider than those found on Earth, indicating faster spreading or slower reversal rates. Although no spreading center has been identified, a map of the magnetic anomalies on Mars reveals that the lineations are concentric to the south pole.

Mantle plume origin

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A process similar to seafloor spreading has been proposed to explain the presence of the concentric stripes around the Martian south pole. The process is that of a single large mantle plume rising in one hemisphere and downwelling in the opposite hemisphere. In such a process, new crust produced would be emplaced in concentric circles spreading radially from a single upwelling point, consistent with the pattern observed on Mars. This process has also been invoked to help explain the Martian hemispheric dichotomy.[14]

Dike intrusion origin

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An alternative hypothesis claims that the magnetic anomalies on Mars are the result of successive dike intrusions due to lithospheric extension. As each dike intrusion cools, it would acquire thermoremanent magnetization from the planet's magnetic field. Successive dikes would be magnetized in the same direction, until the magnetic field reverses its polarity, resulting in the subsequent intrusions recording the opposite direction. These periodic reversals would require that the dike intrusions migrate over time.[17]

Accretion of terranes

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Another study assumes a process of crustal convergence instead of generation, arguing that the magnetic lineations on Mars formed at a convergent plate margin through collision and accretion of terranes. This hypothesis suggests that the magnetic lineations on Mars are analogous to the banded magnetic anomalies in the North American Cordillera on Earth. These terrestrial anomalies are of similar geometry and size as those detected on Mars, with widths of 100–200 km.[18]

Tectonic implications of Valles Marineris

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Satellite imagery of the Valles Marineris trough system, showing an interpreted large scale strike-slip fault system running along its length.[5] Relative fault motion is suggested in part by the offset rim of an old impact basin. Image modified from NASA/MOLA Science Team.

Recent research claims to have found the first strong evidence for a plate tectonic boundary on Mars.[5] The discovery refers to a large-scale (>2000 km in length and >150 km in slip) and quite narrow (<50 km wide) strike-slip fault zone in the Valles Marineris trough system, referred to as the Ius-Melas-Coprates fault zone (Fig. 7). The Valles Marineris trough system, which is over 4000 km long, 600 km wide, and up to 7 km deep, would, if located on Earth, extend all the way across North America.[4]

The study indicates that the Ius-Melas-Coprates fault zone is a left-slip transtensional system similar to that of the Dead Sea fault zone on Earth.[5] The magnitude of displacement across the fault zone is estimated to be 150–160 km, as indicated by the offset rim of an old impact basin. If normalizing the magnitude of the slip to the surface area of the planet, the Ius-Melas-Coprates fault zone has a displacement value significantly larger than that of the Dead Sea Fault, and slightly larger than that of the San Andreas Fault. The lack of significant deformation on both sides of the Ius-Melas-Coprates fault zone over a distance of 500 km suggests that the regions bounded by the fault behave as rigid blocks. This evidence essentially points to a large strike-slip system at a plate boundary, in terrestrial terms known as a transform fault.[5]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Tectonics of Mars

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The tectonics of Mars refers to the geological processes involving crustal deformation, faulting, and volcanism that have shaped the planet's surface over billions of years, primarily through vertical tectonics rather than the horizontal plate movements seen on Earth. Unlike Earth, Mars lacks active plate tectonics, with its crust functioning as a single, rigid plate that has undergone fracturing and warping due to internal cooling, volcanic loading, and possible ancient crustal recycling mechanisms. The Martian crust averages 42–56 km in thickness globally, varying from about 10 km in impact basins to over 70 km in the southern highlands, and exhibits layered substructures at least locally. It bears evidence of these processes in features such as the massive Tharsis bulge—a volcanic province that has caused regional subsidence and radial fault systems—and the hemispheric dichotomy dividing the smoother northern lowlands from the cratered southern highlands. Early Martian tectonics, dating back over 3 billion years to the and periods, likely involved more dynamic activity, including potential vertical tectonics where sections of the crust delaminated and recycled into , fostering diverse with silica-rich magmas that produced stratovolcanoes, lava domes, and calderas in regions like the Eridania basin. This contrasts with the predominantly basaltic shield associated with later epochs and suggests parallels to Earth's Archaean-era crustal evolution before the onset of . Prominent tectonic landforms include grabens, wrinkle ridges, and thrust faults, many linked to the gravitational loading of , which spans nearly a quarter of the planet's surface and has influenced global stress fields. More recent tectonic activity persists on Mars, albeit at a subdued level, as evidenced by young fault systems like Cerberus Fossae, a 1,000-kilometer-long network formed less than 10 million years ago through extensional stresses possibly tied to volcanic or hydrothermal processes. NASA's lander, operating from 2018 to 2022, detected over 700 marsquakes, including magnitudes up to 4.7, primarily from the Cerberus Fossae region, confirming ongoing seismic activity driven by crustal stresses rather than plate boundaries. These findings indicate that while Mars' global tectonic engine has largely stalled—likely due to its smaller size and faster heat loss compared to —localized deformation continues, offering insights into planetary cooling and the potential for preserved ancient signals in tectonic terrains.

Overview

Definition and Scope

Tectonics on Mars encompasses the study of crustal deformation, stress regimes, and the resulting structural features that shape the planet's . This includes the formation of faults, fractures, folds, and other landforms driven by a combination of endogenic (internal) and exogenic (external) forces acting on the Martian crust. Unlike dynamic processes on other bodies, Martian is characterized by episodic activity rather than continuous global renewal, reflecting the planet's smaller size, rapid cooling, and lack of a current global . Mars exhibits a stagnant lid tectonic regime, in which the rigid acts as an immobile "lid" over a convecting mantle, contrasting sharply with Earth's mobile . In this mode, there are no active zones, centers, or lateral plate motions that recycle crust; instead, heat loss occurs primarily through conduction and localized . This stagnant lid has dominated Martian for much of its , likely since around 4 billion years ago, limiting widespread resurfacing and preserving ancient crustal structures. The primary tectonic processes on Mars involve volcanic loading, where massive igneous provinces like exert gravitational stress on the , inducing flexural bending and extensional fractures. Impact events contribute through shock-induced deformation and isostatic rebound, while internal stresses from , planetary cooling, and early despinning generate compressional and extensional features such as systems (normal fault-bounded troughs) and lobate scarps (thrust fault escarpments). These mechanisms have produced a diverse array of structures, including radial grabens around volcanic centers and wrinkle ridges in basin fills. The modern understanding of Martian tectonics originated with the orbiter mission in 1971, which first imaged extensive tectonic landforms, including the vast canyon system and surrounding fault networks, revealing that Mars' surface had been profoundly modified by deformational processes beyond impacts and volcanism alone. These early observations introduced key terminology, such as "lobate scarps" for compressional scarps and "graben systems" for extensional rifts, establishing the framework for subsequent studies. One prominent outcome of these ancient processes is the hemispheric dichotomy, the stark elevation contrast between the southern highlands and northern lowlands.

Comparison to Earth

Both Mars and display tectonic features shaped by internal stresses, including normal and thrust faults, as well as compressional folds like wrinkle ridges, which form due to crustal deformation. Volcanism has also influenced tectonics on both planets, with magmatic intrusions and eruptions contributing to surface uplift, fracturing, and the development of volcanic edifices that interact with surrounding fault systems. These shared elements reflect fundamental processes of planetary cooling and differentiation, though expressed differently due to each body's size and thermal history. A primary difference lies in the absence of global on Mars, where the behaves as a stagnant lid over a convecting mantle, in contrast to Earth's mobile plates driven by vigorous . This Martian style emphasizes vertical tectonics, such as isostatic and radial fracturing induced by the loading of the volcanic province, rather than horizontal plate motions. The divergence stems from Mars' smaller size, which led to thinner and more rapid early cooling, limiting the necessary for sustained plate recycling. Evidence from crustal magnetization indicates that Mars once possessed an active dynamo-generated , similar to Earth's current one, which ceased around 4 billion years ago due to core cooling and solidification. This early dynamo likely supported more dynamic convection and possibly episodic plate-like motions during Mars' period, but its shutdown correlates with the transition to a rigid, immobile and the dominance of localized . Earth's ongoing dynamo, sustained by a hotter core and plate-driven heat loss, continues to facilitate global . Global models indicate an average crustal thickness of 42-56 km, thicker in the southern highlands (up to ~90 km) and thinner in the northern lowlands, compared to Earth's (5-10 km) and (30-70 km). Impacts have modified the crust on both planets, but their effects are more pronounced on Mars, where the lack of prevents recycling of impact-altered material.

Surface Provinces

Southern Highlands

The southern highlands of Mars constitute a vast physiographic province covering more than 60% of the planet's surface, primarily south of approximately -18° latitude, and extending into parts of the such as Arabia Terra and Terra Sabaea. This region features rugged, elevated terrain with average elevations ranging from 0 to 8 km above the Martian datum, contrasting sharply with the lower-lying northern lowlands. The highlands are characterized by densely packed impact craters, many dating to the period (approximately 4.1 to 3.7 billion years ago), reflecting intense early bombardment that shaped the ancient crust. Key tectonic features include large ancient impact basins, such as the partially exposed (diameter ~2,400 km), (~900 km), and Isidis Planitia (~1,500 km), which dominate the landscape and attest to the region's cataclysmic formative history. Superposed on this cratered terrain are compressional structures like wrinkle ridges and lobate scarps, exemplified by the Hellespontes Montes surrounding Hellas, formed through early crustal shortening likely driven by global contraction or isostatic responses to loading. These features indicate a period of significant horizontal compression in the crust, with ridge orientations often reflecting regional stress fields from mantle dynamics. The formation of the southern highlands involved heavy meteoritic bombardment during the , followed by isostatic adjustment that thickened the crust to an average of about 57 km, with local variations up to 60 km or more in elevated areas. This process stabilized the terrain early in Martian history, resulting in a dominantly ancient surface with minimal subsequent modification. Volcanic resurfacing was limited, confined mostly to early and middle edifices and scattered late flows, underscoring a transition to tectonic quiescence after the period, when global activity waned dramatically.

Northern Lowlands

The northern lowlands of Mars, located primarily north of approximately 18°N latitude, represent a vast topographic depression covering about 30% of the planet's surface, with elevations ranging from -5 to 0 km relative to the Martian datum. This region includes major basins such as and Acidalia Planitia, characterized by extremely low relief and smooth plains that contrast sharply with the elevated southern highlands. The lowlands' formation involved significant infilling during the period, masking older crustal structures and contributing to the planet's hemispheric dichotomy. Tectonic features in the northern lowlands primarily reflect later volcanic and sedimentary processes rather than intense early deformation. Widespread volcanic flooding during the early deposited thick plains units, interpreted as basaltic lavas emanating from sources possibly linked to but not detailed here, which smoothed the basin floors. Overlying these are possible sedimentary infills, including the Vastitas Borealis Formation, a thin veneer of late deposits likely sourced from massive outflow channel floods that transported water and sediments into the basins. Subtle wrinkle ridges, formed by -era compressional stresses, deform these units with typical heights of 50-300 m and spacings of ~80 km, indicating regional contraction without the prominence seen in highland terrains. The combined sedimentary and volcanic fill in the northern lowlands reaches depths of up to 10 km in major basins, contributing to a thinned crust estimated at ~30 km thick, compared to thicker highland crust. This infill has buried early or older crust, preserving remnant magnetic anomalies from the planet's ancient in localized high-northern latitude patches. for past oceans or megafloods includes shoreline-like features, outflow channel termini, and hydrated minerals in the plains, which smoothed the through and deposition. The region's minimal crater density, with many surfaces dating to the Amazonian period, points to ongoing resurfacing by volcanic flows, eolian processes, and possible glacial activity that has preserved the lowlands' youthful appearance.

Tharsis Plateau

The Plateau is a vast volcanic and tectonic province situated in the equatorial of Mars, extending over approximately 30 million square kilometers and spanning about 5,000 km in diameter. This elevated region rises to heights of up to 10 km above the planetary mean radius, forming one of the most prominent topographic features on the planet. The plateau hosts major volcanic shield complexes, including the Tharsis Montes (Ascraeus Mons, Pavonis Mons, and Arsia Mons) and the immense , the largest volcano in the Solar System. These structures are accompanied by extensive radial systems, which result from induced by the massive volcanic load. Formation of the Tharsis Plateau is attributed to prolonged activity initiating in the period, which drove massive igneous eruptions, isostatic uplift, and circumferential compression of the surrounding . This process generated a total erupted volume of approximately 3 × 10^8 km³, accounting for a substantial portion of Mars' current rotational bulge. The resulting stresses from this uplift are believed to have influenced the development of nearby features such as .

Other Key Provinces

Elysium Planitia, located in the northeastern quadrant of Mars, represents a secondary volcanic characterized by a cluster of low-relief shield volcanoes, including , Albor Tholus, and Hecates Tholus, which form the second-largest volcanic complex on the planet after . These features include small shields and volcanic domes, indicative of late-stage effusive that persisted into the Amazonian period. Tectonic signatures in the region encompass grabens and linear fault depressions, often radial to the volcanic centers, suggesting localized extension possibly linked to subsurface plume activity and uplift. Evidence from seismic data recorded by the lander further supports contemporaneous volcanic and tectonic processes in Elysium Planitia. Hellas Planitia, situated in the southern highlands, is a vast impact basin approximately 2,300 km in diameter and reaching depths of up to -7 km, making it the deepest topographic depression on Mars. Formed around 4.0–4.2 billion years ago during the Noachian period, the basin's excavation triggered significant post-impact tectonics, including isostatic rebound that produced radial and circumferential faults, as well as thrust faulting along its margins. These structures reflect compressional stresses from the impact and subsequent lithospheric adjustments, with wrinkle ridges and lobate scarps indicating episodic deformation extending into later epochs. Arabia Terra serves as a transitional zone between the southern highlands and northern lowlands, featuring densely cratered terrain with numerous ancient impact structures dating back to the era. Prominent tectonic and erosional features include inverted channels—sinuous ridges formed by the differential wind erosion of less resistant surrounding materials, exhuming former fluvial deposits. These landforms, along with minor faulting and pedestal craters, highlight prolonged surface modification through erosion rather than dominant endogenic tectonics, though subtle stresses from nearby basins like Hellas contributed to regional fracturing. Collectively, these provinces exhibit episodic tectonic activity, with Hellas Planitia's formation around 4 billion years ago generating regional stresses that influenced fault patterns in adjacent areas.

Hemispheric Dichotomy

Morphological and Hypsometric Features

The hemispheric dichotomy on Mars is defined by a pronounced contrast in elevation between the southern highlands and northern lowlands, with the former averaging approximately +2.5 km above the planetary datum and the latter -3 km, resulting in an overall topographic difference of about 5.5 km. This bimodal reflects the planet's global-scale topographic asymmetry, where the occupies roughly two-thirds of the surface and rises gradually to form rugged terrain, while the northern plains form a vast basin-like depression. Morphologically, the southern highlands are characterized by densely packed impact craters exceeding 10 km in , many of which are heavily degraded and date to the period, contributing to a heavily modified, undulating landscape. In contrast, the northern lowlands consist of smooth, sparsely cratered plains primarily composed of volcanic and sedimentary deposits from the and Amazonian periods, with fewer large craters due to resurfacing processes. The transition between these provinces occurs along a irregular boundary near 30°N latitude, marked by a 1-2 km high , fretted terrain featuring isolated mesas and knobs, and chaotic terrains with jumbled blocks indicative of or erosional dissection. Crustal thickness varies significantly across the , with the southern highlands exhibiting an average of about 50 km based on gravity modeling from data, compared to roughly 30 km in the northern lowlands, underscoring the structural basis for the divide. These estimates derive from admittance analysis correlating gravity anomalies with , assuming Airy isostatic compensation and a crustal of around 2.9 g/cm³. Additionally, the southern highlands display stronger crustal magnetic anomalies, consistent with their thicker, older crust. This influences nearly the entire , with the transitional features highlighting a complex boundary zone shaped by prolonged geological activity.

Endogenic Formation Theories

Endogenic formation theories for the Martian hemispheric emphasize internal planetary processes, such as mantle dynamics, that could have generated the observed crustal thickness and elevation contrasts between the northern lowlands and southern highlands during Mars' early . These models propose that asymmetric convection or localized thermal anomalies in led to differential crustal production and modification, without relying primarily on external impacts or . Such mechanisms are supported by geophysical modeling that aligns with the planet's small and rapid cooling, which would have limited prolonged tectonic activity. One prominent endogenic model involves degree-1 , where a large-scale, hemispheric in flow produces an in the that thins the crust through enhanced and resurfacing, while a corresponding in the southern hemisphere promotes crustal thickening via reduced melting and potential subduction-like processes. This pattern is thought to have initiated shortly after Mars' accretion around 4.5 billion years ago (Ga), driven by factors such as an endothermic at the core-mantle boundary or initial compositional heterogeneities. Numerical simulations indicate that this mode of could establish the within the first 100 million years (Myr) of planetary history, consistent with the lack of later major resurfacing events. Another proposed mechanism is the , interpreted here through its endogenic consequences, where a massive collision forming the Borealis basin excavates and removes much of the northern crust, followed by isostatic rebound and mantle upwelling that further thins the in that region. This process would redistribute material internally, with the impact-induced heating triggering convective adjustments that amplify the hemispheric contrast. Modeling suggests this could occur during the late stages of accretion, around 4.5 Ga, aligning with the elliptical shape of the northern lowlands and the absence of a central peak or ring structures typical of smaller basins. Early plume activity represents a related endogenic process, wherein localized plumes generate intense heating that erodes and thins the northern through widespread and volatile release, while the remains relatively stable. Such plumes, potentially arising from core-mantle boundary instabilities, could have focused and crustal recycling in the north, contributing to the topographic . This model integrates with observations of early volcanic provinces and predicts formation timescales of 100-500 Myr post-accretion. Overall, these endogenic models collectively predict dichotomy formation within the first 100-500 Myr of Mars' history, a timeframe corroborated by isotopic of southern highland crust, which reveals ages as old as approximately 4.5 Ga, indicating minimal subsequent modification. In contrast to exogenic models, endogenic theories better account for the deep-seated crustal thickness variations observed via data.

Exogenic Formation Theories

Exogenic formation theories for the Martian hemispheric propose that external processes, such as impacts, , and resurfacing, primarily shaped the planet's north-south crustal and topographic divide without relying on deep internal mantle dynamics. These models emphasize surface or near-surface modifications during the period (approximately 4.1–3.7 Ga), when Mars experienced intense bombardment and early climatic activity. Observations from orbital data, including anomalies and stratigraphic mapping, support the idea that up to 5 km of topographic relief and 15–30 km of crustal thickness variation arose from material excavation or redistribution in the . One prominent exogenic mechanism involves widespread and deposition, particularly by aqueous processes, which stripped material from what were originally highlands in the north and deposited it into basins. During the , regional along the boundary, possibly facilitated by a transient or episodic flooding, removed substantial volumes of —estimated at around 57,000 km³ over an area of 284,000 km² west of Ares Vallis alone—leaving isolated remnant mounds that were once part of contiguous highland plateaus like Mawrth Vallis. This retreat of the boundary hundreds of kilometers southward occurred between 4.0 and 3.7 Ga, with phyllosilicate-rich deposits (~350 m thick) preserving evidence of water-rock interactions and . Models indicate that such could account for 1–10 km of net material removal across the northern lowlands, consistent with volumes inferred from lowland fill and hypsometric profiles showing the north as a thinned, basin-like . Wind-driven processes may have contributed secondarily, but aqueous dominates as the primary agent in these scenarios. Another exogenic hypothesis attributes the dichotomy to the cumulative effects of multiple large impacts concentrated in the , excavating and thinning the crust through overlapping basin formation. Proposed in the early , this model suggests that a series of giant impacts during the (~4.0–3.8 Ga) created the broad lowland expanse, with basin rims partially defining the irregular boundary. While it explains some topographic details, such as the external portions of the lowlands beyond single-basin margins, the hypothesis requires supplementary resurfacing or to fully account for the smoothed northern plains and lack of prominent rim structures. and topographic data indicate that these impacts could have removed 10–20 km of crust locally, contributing to the overall 26 km thickness contrast observed today. Volcanic resurfacing represents a complementary exogenic process, where preferential lava flooding masked and infilled older northern terrain, enhancing the elevation contrast with the southern highlands. Linked to early plume activity migrating from higher latitudes toward the equator around 3.9–3.5 Ga, this resurfacing produced vast smooth plains that embay ancient massifs, infill large craters, and erase magnetic signatures in the north—features absent in the cratered southern crust. The volume of basaltic lavas required aligns with ' total output (~3 × 10^8 km³), with northern deposits estimated at several kilometers thick, supporting models where up to 5 km of volcanic cover contributed to the hypsometric . This mechanism is particularly effective in explaining the relatively young crater ages (~3.8 Ga) and subdued of the lowlands.

Crustal Magnetism

Characteristics of Magnetic Anomalies

The remnant crustal magnetic field of Mars was comprehensively mapped by the Mars Global Surveyor (MGS) spacecraft's magnetometer instrument between 1999 and 2006, revealing a globally distributed but highly heterogeneous pattern of anomalies observed at altitudes of approximately 400 km. These measurements indicate that Mars lacks a present-day global dynamo-generated field but retains intense localized crustal magnetism, primarily in the form of alternating positive and negative anomalies that reflect variations in the remanent magnetization of ancient rocks. The anomalies are characterized by their linear and striped morphologies, with individual features extending from 100 to 1,500 km in length, often aligned roughly parallel to lines of latitude in the southern hemisphere. The strongest magnetic anomalies are concentrated in the Noachian-aged southern highlands, where field intensities reach up to 200-250 nT at 400 km altitude, contrasting sharply with the northern lowlands, where anomalies are weak or entirely absent. This hemispheric asymmetry correlates with the planet's ancient crustal , with robust signals overlying old, heavily cratered terrains but showing notable absences beneath major volcanic provinces like and the large impact basins (Hellas, Argyre, and ). The magnetization intensities required to produce these observed fields range from 10 to 100 A/m, implying a thick layer of magnetized crust, potentially up to 50 km deep in some regions, far exceeding typical terrestrial crustal magnetization. These magnetic anomalies formed during episodes of dynamo activity in Mars' early history, approximately between 4.5 and 3.7 billion years ago, when thermoremanent magnetization was acquired in iron-rich minerals within the cooling crust under the influence of an active core ; recent studies suggest the dynamo persisted until at least 3.7 Ga. Subsequent demagnetization has modified this signal, with large impacts causing shock-induced and erasure over diameters exceeding 1,000 km, and widespread reheating and overwriting the magnetic imprint in younger terrains. The preserved anomalies thus provide a snapshot of the planet's magnetic history, highlighting regions that escaped significant alteration since the dynamo ceased.

Mantle Plume Interpretations

One prominent interpretation of Martian crustal magnetic anomalies posits that they result from the interaction between rising mantle plumes and the lithosphere during the planet's early history. In this model, hot mantle plumes ascend from the core-mantle boundary, heating the overlying crust to temperatures exceeding the Curie point of magnetic minerals (approximately 580°C for magnetite), thereby thermally demagnetizing previously magnetized regions. Alternating episodes of upwelling and quiescence, combined with potential lithospheric drift over fixed plumes, produce striped or linear magnetic patterns as "hot spot tracks," where magnetized crust alternates with demagnetized zones formed during plume activity. This process contrasts with more localized demagnetization from dike intrusions, as plumes induce broad-scale thermal alteration across hundreds of kilometers. Supporting evidence for this plume-driven mechanism emerges from the of magnetic anomalies, particularly their alignment with proposed plume tracks beneath the hemispheric transition zone. High-amplitude anomalies in the southern highlands exhibit elongated, east-west trending lineations that form concentric patterns centered near the of thickened southern crust (approximately 76.5° E, 84.5° S), consistent with radial spreading of plume-induced crustal material. These lineations, observed in Mars Global Surveyor magnetometer data, suggest that degree-1 —dominated by a single large plume—generated alternating polarity stripes as new crust cooled in the presence of a reversing field. The absence of strong anomalies in the northern lowlands further implies widespread demagnetization by plume , which thinned the and homogenized magnetization in that region. Mantle plume activity is inferred to have peaked around 4.0 billion years ago, coinciding with the later phases of Mars' core dynamo cessation (recently estimated between approximately 4.0 and 3.7 Ga). Plumes likely contributed to crustal thinning in the north by promoting partial melting and isostatic subsidence, while enhancing magnetization preservation in the south through episodic resurfacing. Numerical models of degree-1 convection demonstrate that such plumes can account for the observed magnetic lineation patterns and the overall dichotomy morphology, with the plume center closely matching the southern crustal thickness maximum (within ~245 km). This early plume activity may represent a precursor to later volcanic provinces like Tharsis, where persistent upwellings sustained long-term magmatism.

Dike Intrusion Interpretations

The dike intrusion model posits that linear magnetic anomalies in Mars' crust result from repeated injections of magnetized along faults during the planet's early history, with the intrusions carrying magnetic minerals such as that acquired thermoremanent while the internal was active. These dikes, emplaced as swarms, would form coherent, striped patterns observable in magnetic maps due to their alignment and the contrast in magnetization between the intrusions and surrounding crust. Evidence for this interpretation includes the observed linear anomalies, which are typically 100–200 km wide and parallel to major fault systems in the Noachian crust, suggesting that the dikes exploited pre-existing tectonic weaknesses. The widths of these anomaly patterns align with the scale of terrestrial dike swarms adjusted for Mars' thicker crust and higher magnetization intensities (up to 10 times Earth's crustal values), where multiple parallel dikes spaced 10–50 km apart could collectively produce the observed signals. Modeling indicates that a minimum crustal layer thickness of 35–60 km is required to sustain the anomaly amplitudes, consistent with early Martian crustal structure. Tectonically, these intrusions are linked to episodes of global extension and associated crustal thinning, likely driven by internal heating and mantle that induced rifting across the planet's surface around 4 billion years ago. This extension facilitated ascent along reactivated faults, contributing to the hemispheric through localized thinning in the northern lowlands while building thickened crust in the south. These intrusions may also delineate boundaries between accreted terranes in the southern highlands.

Terrane Accretion Interpretations

One interpretation of Mars' crustal magnetic anomalies attributes them to the accretion of distinct s during the planet's formative stages. In this model, Proto-Mars formed through the assembly of magnetic fragments—likely a mosaic of proto-continents and oceanic-like crust—that collided at convergent margins, leaving linear and banded anomalies as markers of suture zones where these s were sutured together. This process resembles accretion on Earth, such as the assembly of the , but occurred on a global scale early in Martian history. Supporting evidence derives from the patchy and irregular distribution of magnetic anomalies mapped by the spacecraft, concentrated in the ancient southern highlands. These anomalies exhibit discrete patches of alternating polarity and intensity, consistent with multiple independent crustal blocks that were magnetized separately before incorporation into the southern crust, suggesting the presence of 5–10 such terranes. The absence of similar features in the northern lowlands further supports a tectonic origin tied to early crustal assembly rather than uniform planetary cooling. Tectonically, these collisions would have generated widespread compression, leading to crustal shortening and thickening predominantly in the , which may have contributed to the development of the hemispheric by enhancing topographic contrasts across the planet. Models indicate that terrane accretion transpired approximately 4.5 billion years ago, contemporaneous with the onset of Mars' core , allowing the anomalies to preserve primary thermoremanent from that era before the field weakened around 4.0 billion years ago or later.

Major Tectonic Features

Valles Marineris

Valles Marineris represents one of the most prominent extensional tectonic features on Mars, manifesting as a vast system of interconnected canyons that exemplifies the planet's crustal response to regional stresses. This canyon complex extends approximately 4,000 km along the Martian equator, with widths reaching up to 200 km and depths plunging to 7 km in places, making it vastly larger than Earth's —its total area is about seven times greater, while fault displacements along its boundaries can exceed 10 km. The structure formed primarily during the era, a period marked by significant volcanic and tectonic activity on Mars. The tectonic origin of is attributed to the development of structures driven by extensional forces associated with the uplift of the nearby bulge, which induced horizontal stretching of the Martian . This extension likely initiated as a , where normal faulting created the initial troughs, followed by episodes of vertical and through slumping along the steep walls. The connection to loading underscores how isostatic adjustments from volcanic loading contributed to the regional extension that shaped the canyons. Subsequent modifications, including erosional processes, further deepened and widened the system over time. Prominent features within include extensive layered deposits exposed in the canyon walls and floors, which consist of sedimentary and possibly volcanic materials that record the depositional environment during and after initial rifting. Outflow channels emanating from the eastern segments, such as those leading to Chryse Planitia, suggest episodes of fluid release, likely or subsurface outbursts, that carved additional valleys and indicate hydrological activity tied to tectonic disruption. These elements highlight not only as a tectonic scar but also as a site preserving evidence of Mars' dynamic geological and climatic past.

Tharsis Radial Structures

The radial structures consist of extensive networks of grabens and faults that radiate outward from the volcanic province, primarily manifesting as Solis Fossae and Sirenum Fossae in the southern hemisphere. These features form linear to arcuate troughs, with Solis Fossae extending northeastward and Sirenum Fossae trending southwestward, both centered on volcanic centers such as and Syria Planum. The grabens exhibit widths typically ranging from 1 to 2 km and topographic depths of 100 to 500 m, representing surface expressions of subsurface dike intrusions and crustal fracturing. These structures formed primarily through lithospheric stretching induced by the isostatic adjustment to the massive volcanic loading of the rise, which spans approximately 4 to 3 billion years ago during the Late to Early periods. The accumulation of volcanic material, driven by underlying mantle plumes, generated tensile stresses that propagated outward, causing extensional failure and the development of rift-like grabens over distances of 2,000 to 4,000 km from the center. This process involved both flexural bending of the under the load and localized dike emplacement, with the radial pattern reflecting the symmetric stress field around the rising dome. The scale of deformation indicates a global extensional strain of 1 to 4 percent associated with loading, with individual faults penetrating to depths of up to 2 to 3 km into the crust, based on topographic and geophysical modeling. The patterns of these grabens demonstrate a flexural response to the volcanic load, as evidenced by their concentric and radial orientations relative to topographic highs. Some faults within these networks show evidence of reactivation during the Amazonian period, linked to ongoing volcanic or plume-related activity, though at reduced rates compared to earlier epochs.

Global Fracture Patterns

The global fracture patterns on Mars comprise a diverse array of tectonic structures that record the planet's deformational history, including compressional lobate scarps formed by faulting, extensional grabens resulting from crustal , and transcurrent strike-slip faults accommodating lateral shear. Lobate scarps, characterized by their scalloped, arcuate traces and uplifted scarplet blocks, are widespread in the northern lowlands such as Arcadia Planitia, where they indicate horizontal shortening of the . Extensional grabens, often appearing as parallel troughs bounded by normal faults, dominate in regions like Fossae in , where they form elongated systems up to 1,000 km long due to vertical extension. Transcurrent faults, evidenced by offset linear features and en echelon patterns, occur sporadically across the crust, as documented in Tharsis-margin terrains, reflecting shear-dominated deformation. These fracture systems exhibit pronounced spatial patterns, with extensional grabens and rifts concentrated along equatorial latitudes and compressional scarps and ridges more abundant toward the poles, delineating a hemispheric-scale stress distribution. The cumulative length of mapped faults planetwide surpasses 680,000 km, underscoring the extensive scale of Martian tectonism despite the absence of . This equatorial extension and polar contraction arise from competing principal stress regimes: radial tensile stresses induced by the flexural loading of the bulge, which promotes normal faulting in low-latitude zones, contrasted with circumferentially compressive stresses from planetary cooling and contraction, favoring thrust and wrinkle-ridge formation at higher latitudes. Finite element models of lithospheric stresses confirm that Tharsis-driven tension dominates in the , while global thermal contraction imposes compression globally, with magnitudes up to several hundred MPa in the upper crust. A significant portion of these global fractures formed or were reactivated during the Amazonian period, the most recent spanning the last 3 billion years, implying persistent localized tectonic activity on an otherwise cooling planet. For instance, thrust-related shortening structures in Arabia Terra show multiple episodes of activation over the past 2 billion years, as indicated by overlapping deposits triggered by fault motion. Seismic data from the lander further support this, with marsquakes originating from depths of 15–36 km beneath extensional features like Cerberus Fossae, linking recent to fault reactivation.

Modern Evidence

InSight Seismology

The (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander, deployed by in 2018, touched down on the region of Mars and operated until December 2022, providing the first seismic data from another planet. Equipped with the Seismic Experiment for Interior Structure (SEIS) instrument, a highly sensitive broadband , detected 1,319 marsquakes over its mission lifetime, ranging from low-amplitude signals to events up to magnitude 4.7. These detections revealed a seismically active Martian interior, with more detections at night when atmospheric noise from wind is lower, allowing better recording of seismic signals. Key structural insights from the seismic data include a core radius of about 1,830 kilometers, inferred from the analysis of shear and compressional wave speeds propagating through the planet. Further analysis of data in 2025 confirmed a solid inner with a radius of approximately 613 km, surrounded by a liquid outer core. The crust beneath the landing site is estimated to be approximately 39 ± 8 kilometers thick, varying regionally based on waveform modeling of direct and reflected seismic phases. Additionally, the low seismic velocities observed in the mantle suggest a dry composition with minimal , contrasting with Earth's wetter and indicating limited hydration since Mars' early history. These findings were derived from inverting arrival times and dispersion curves of prominent marsquakes, such as the magnitude 4.7 event S1222a. Tectonically, the InSight data highlight ongoing shallow crustal activity, with many marsquakes originating from the Cerberus Fossae graben system, approximately 1,600 kilometers away from the lander, implying recurrent faulting driven by stresses from the nearby volcanic rise. Event depths are predominantly less than 50 kilometers, with no evidence of deep seismicity akin to plate subduction zones on , supporting a model of localized, non-plate-like tectonics. Seismic velocities further indicate sparse water in the crust, consistent with a desiccated upper mantle that limits brittle failure and promotes aseismic deformation in some regions. These observations align broadly with gravity models of crustal thickness but underscore seismology's unique role in detecting active dynamics.

Gravity and Topographic Data

Gravity and topographic data from orbiting spacecraft have provided critical insights into the structure and dynamics of Mars' crust, revealing variations in density and thickness that inform tectonic processes. The Mars Reconnaissance Orbiter (MRO), launched in 2005 and operational since 2006, has contributed extensively to high-resolution gravity measurements through radio tracking, enabling the development of detailed gravity field models. A seminal model, the Goddard Mars Model 3 (GMM-3), achieves a spherical harmonic degree and order of 120, incorporating data from MRO alongside earlier missions like Mars Global Surveyor and Mars Odyssey to map gravity anomalies at resolutions approaching 100 km. These models, combined with topographic data from the Mars Orbiter Laser Altimeter (MOLA), allow for the separation of crustal and mantle contributions to the gravity field, highlighting isostatic adjustments and lithospheric flexure. Prominent gravity anomalies underscore major tectonic provinces on Mars. The Tharsis volcanic province exhibits a pronounced positive free-air gravity anomaly of approximately +300 mGal, reflecting the dense volcanic load and underlying mantle upwelling that dominate this elevated region. In contrast, the Hellas impact basin displays a significant negative anomaly of about -200 mGal, indicative of low-density crustal material and partial isostatic rebound following excavation. These features confirm the hemispheric crustal dichotomy, with the northern lowlands showing thinner crust and lower elevations compared to the thicker, elevated southern highlands, as derived from admittance analyses that correlate gravity with topography. Tectonic interpretations from these data emphasize lithospheric responses to loading and unloading. Gravity anomalies over reveal flexural support and partial , with a compensation depth of 20-30 km beneath the province, suggesting that volcanic constructs are buoyed by crustal roots while the surrounding bends under the load. Such patterns indicate that tectonic stresses from Tharsis emplacement influenced global fracture systems and regional warping, with the anomalies providing evidence for viscoelastic relaxation over geological timescales. Updated models from the 2020s, building on MRO , refine crustal thickness estimates and bolster models of an endogenic origin for the . The southern hemisphere averages about 58 km in crustal thickness, compared to roughly 32 km in the north, supporting scenarios involving degree-1 that thickened the southern crust through prolonged . These gravity-derived thicknesses align broadly with seismic estimates of crustal structure from the mission, reinforcing a consistent view of Mars' interior layering.

Tectonic Evolution

Noachian Era

The Noachian Era, spanning approximately 4.1 to 3.7 billion years ago, marked the initial formation and stabilization of Mars' primary crust following the solidification of a global magma ocean, which occurred shortly after planetary accretion around 4.5 billion years ago. This period was characterized by intense meteoritic bombardment, including the formation of major impact basins such as Hellas and Argyre, which contributed to widespread crustal fracturing and the excavation of deep megaregolith layers in the southern highlands. Concurrently, an active core dynamo generated a global , imprinting strong crustal magnetizations that are preserved as magnetic anomalies today, particularly in the where the crust remained intact. Tectonic processes during this era were dominated by impact-induced fracturing, which created extensive networks of faults and grabens across the nascent crust, while the early initiation of the —evident in the topographic contrast between the elevated southern highlands and the northern lowlands—likely arose from asymmetric crustal thickening or giant impact events that redistributed material. These impacts also facilitated the formation of magnetic anomalies through shock remanent magnetization of iron-rich minerals in the cooling crust, with the remaining active until at least the late . Proto-Tharsis plumes, driven by early , began to influence regional tectonics by inducing localized uplift and extensional stresses in the southern highlands, setting the stage for later volcanic activity. The southern highlands, heavily saturated with craters larger than 32 km in diameter, preserve the record of this bombardment, with the vast majority—over 90%—of Mars' large impact structures forming during the and contributing to a global contraction of approximately 0.1% strain as the cooled. This contraction manifested in subtle compressional features amid the dominant extensional fracturing, reflecting the thermal evolution from a hot, convecting interior to a more rigid .

Hesperian Era

The Hesperian Era, spanning approximately 3.7 to 3.0 billion years ago, represented a period of peak tectonic and volcanic activity on Mars, characterized by the rapid growth of the volcanic province and associated deformational processes. This era saw the emplacement of vast volumes of lavas, estimated at around 3.3 × 10^7 km³ in the ridged plains units alone, which resurfaced significant portions of the southern highlands and northern lowlands. The loading from volcanism, a massive rise spanning roughly 8000 km in diameter and up to 10 km in elevation, induced flexural stresses that drove widespread extension across the , contributing to an estimated 1-2% global extensional strain. Central to Hesperian tectonics was the opening of , a ~4,000-km-long extensional system that formed along radial fractures peripheral to , involving deep-seated faulting, , and erosional widening to depths of up to 9 km. This rifting was exacerbated by gravitational spreading of the bulge, with fault displacements reaching 0.5-4.5 km in regions like and Syria Planum, and was contemporaneous with intrusive magmatism that facilitated volatile release. Compressional features, such as wrinkle ridges, emerged in response to lithospheric shortening induced by volcanic loading and isostatic adjustments, with these structures—typically 1-4 km deep décollements—forming concentrically around and achieving shortening strains of 0.2-0.5% over hundreds of kilometers in areas like Lunae Planum. Widespread flooding events, triggered by tectonic fracturing and cryovolcanic outbursts, carved major outflow channels such as Kasei Valles and Mangala Valles, releasing subsurface aquifers through breaches in chaotic terrains adjacent to . These channels, sourced from elevated regions like at ~3.5 km altitude, facilitated the redistribution of at least 7.5 × 10^6 km³ of , forming temporary basins in the northern plains and eroding Hesperian intercrater terrains. The Hesperian ridged plains, emblematic of this era's flood-style , exhibit subtle lobate scarps and thrust faults that record the interplay of extension and compression, with volcanic resurfacing rates peaking at ~1 km² per year before transitioning to the more subdued Amazonian quiescence.

Amazonian Era

The Amazonian Era, spanning from approximately 3.0 billion years ago to the present, represents a period of relative tectonic quiescence on Mars, characterized by diminished global activity compared to earlier epochs, yet punctuated by episodic , localized faulting, and evidence of ongoing contraction due to planetary cooling. During this time, the planet's interior heat loss slowed significantly, leading to a predominantly stagnant lid tectonic regime with limited resurfacing, where less than 1% of the surface shows modifications attributable to processes within the last 10 million years. Cumulative effects from and loading, such as the bulge, influenced the distribution of stresses, but Amazonian tectonics primarily involved low-volume, localized deformation. Late-stage volcanism in the Tharsis region persisted into the Amazonian, with distributed dike-fed eruptions forming over 650 small volcanoes, many dated to less than 200 million years ago through crater counting. These edifices, associated with major shields like (average age ~69 Ma) and (~202 Ma), indicate episodic ascent along radial and circumferential dike swarms, contributing to minor extensional stresses. In , young basaltic lava flows from Cerberus Fossae fissures, such as those in Athabasca Valles (~2.5–20 Ma) and Marte Vallis (~9 Ma), cover areas totaling thousands of cubic kilometers and demonstrate recent effusive activity linked to mantle . True polar wander, driven by mass redistribution from this late volcanism, likely occurred during the late Hesperian to early Amazonian transition, reorienting the spin axis by 5–10° to align paleopolar deposits, such as the Dorsa Argentea Formation, with volcanic loads equivalent to ~4.4 × 10¹⁹ kg of lava. Localized extension dominated in regions like Cerberus Fossae, where grabens and normal faults formed as recently as <20 Ma, potentially triggered by dike intrusion or residual Tharsis stresses, producing fresh scarps and boulder tracks indicative of seismic activity. Complementing this, global contraction from interior cooling has generated compressional features, including lobate scarps and wrinkle ridges, with some fault reactivations extending into the Amazonian, as evidenced by overlapping small grabens on older thrusts. Seismological data from the mission (2018–2022) confirm recent tectonic activity, detecting over 47 repetitive low-frequency marsquakes (magnitudes 2–4) sourced to Cerberus Fossae, implying ongoing mobility and possible magma-related slip rather than purely crustal faulting. These events, clustered in families with similar waveforms, suggest episodic fault activation within the last few million years, underscoring that Mars retains a dynamically evolving interior despite its overall tectonic dormancy.

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