Long-Term Evolution of the Martian Crust-Mantle System (original) (raw)

The Dual Nature of the Martian Crust: Young Lavas and Old Clastic Materials

Visible and thermal infrared spacecraft datasets are used to gain insight into the nature of the surface materials and upper martian crust, revealing a distinct transition in the physical properties of martian crustal materials that occurred during the Hesperian era. Contrary to a prevailing view of the martian crust as primarily composed of lava flows, we find that most older regions of Mars have morphological and thermophysical properties consistent with poorly consolidated fine-particulate materials that may have a volcaniclastic origin. By contrast, younger surfaces contain blocky materials and thermophysical properties consistent with effusive lava flows. Explosive volcanism is likely to have been dominant on early Mars and these findings have implications for the evolution of the volatile content of the crust and mantle and subsequent development of the surface morphology. This dual nature of the crust appears to be a defining characteristic of martian history.

The petrological expression of early Mars volcanism

Crystallization products of liquids produced by partial melting of a possible Martian mantle for conditions covering the earliest Noachian era to the most recent Amazonian times have been modeled using the MELTS thermodynamic calculator. The results imply a transition from low-calcium pyroxene dominated assemblages in the Noachian to high-calcium pyroxene assemblages in the Hesperian and Amazonian, which is remarkably consistent with observations made by orbiting visible and near-infrared spectrometers. This transition is interpreted as the consequence of the thermal evolution of the mantle, with no need for exotic conditions, such as higher water content or nonchondritic Ca/Al ratio of the mantle source, to produce low-calcium pyroxene rich lithologies. Our results are compatible with numerical models of the thermal evolution of Mars that predict high production rates of crust on early Mars, implying that Noachian rocks exposed at the surface may be petrological expressions of this volcanism rather than being associated with mantle overturn following the crystallization of a magma ocean.

The evolution of volcanism, tectonics, and volatiles on Mars-an overview of recent progress

Lunar and Planetary …, 1991

Among the principal accomplishments of the M E W project are several important and widely accepted scientific findings about Mars. The global and regional volcanic flux has been established from systematic geological mapping using V i g images, providing a relative volcanic chronology for most of martian history. Petrologic and chemical analyses of SNC meteorites, inferred to have been derived &om Mars, have revealed an abundance of volatile materials, including hydrous minerals (amphiboles), oxidized sulfur, possible carbonates, and various salts; these results provide direct evidence that Mars is likely to be ~olatile~rich. Geological mapping and temporal groupings of major fault systems have provided strong new c o n s b t s on the sequence and timing of martian tectonic events, particularly in the vicinity of the Tharsis region. Substantial progress was also forthcoming on several fundmental but incompletely resolved aspects of martian evolution during the MEVTV program. The origin of the crustal dichotomy on Man was the subject of intensive investigations, and two classes of hypotheses have emerged: One relates the northern lowlands to the effects of l q e impact(s); the other calls for tectonic foundering subsequent to subcrustal erosion by mantle convection. The kinematics and mode of formation of wrinkle ridges are the subjects of continuing research. While it is clear that these features represent compressional deformation, whether they are predomhantly the expression of buckling or faulting remains problematic, as do the cause and implications of their remarkably straight trends and periodic spacing in some locales. Isotopic and petrologic analyses have revealed significant variations within the group of SNC meteorites that, if these objects come from Mars, suggests heterogeneous sources for the parental martian magmas. Finally, several intriguing new ideas have resulted from project-sponsored research and workshop discussions. A number of tectonic features have been identi£ied as probable transcurrent faults documenting horizontal offsets of at least several tens of kilometers. Such faulting, along with the large extensional strains required to form Valles Marineris, could indicate an early episode of significant horizontal motions of lithospheric blocks. One speculative hypothesis is that such motions were accommodated in a very early episode of plate tectonics on Mars, during which the original lithosphere of the northern lowlands was subducted beneath the Tharsis region and new lithosphere with thinner crust was generated at a now-extinct spreading center. This hypothesis, which remains to be tested rigorously, links the formation of the crustal dichotomy to the formation of Tharsis. INTRODUrnON The organjzation of the MEVm project was styled after that Mars has been the target of a number of ambitious spacecraft of the successful MECA project. It combined elements of a missions, including the American Viking orbiters and landers project approach and targeted research by independent in the late 1970s and, more recently, the m e t Phobos investigators. Specific goals and objectives were defined from spacecraft in 1989. Soon after the Viking mission it became the project perspective, but investigators were funded clear that data from that mission would constitute a long-term individually and operated independently within the context of source of important information about the nature and the study. The first meeting of the M E W project was held evolution of Mars. In recognition of this potential, NASA in the spring of 1987, where a science steering committee was established the Mars Data Analysis Program (MDAP) in 1979 chosen and general guidelines for the project were defined. to coordinate the funding and the direction of Mars research. ~artici~ation-in M * was open to-all investigators with The first of several major thematic investigations supported by research interests encompassed by the goals of the project, MDAP was a focused three-year study project entitled "Mars: regardless of funding source, to ensure broad-based involve-Evolution of its Climate and Atmosphere" (MECA), initiated ment. A program of workshops was organized to provide in 1984 under the direction of the Lunar and Planetary cohesion to the project and to ensure that the project's Institute in Houston, Telras. The success of the MECA project objectives would be addressed (Table 1). The MEVTV project (CIiffwd et d., 1988a,b) led to a follow-on three-year study provided a rich environment for collaborative efforts between project entitled "Mars: Evolution of Volcanism, Tectonics, and investigators from very diverse fields of investigation, often Volatiles" (MEVTV), initiated by NASA in 1987, also under the resulting in new approaches to d8icult problems related to direction of the Lunar and Planetary Institute. the study of Mars.

Post-Viking View of Martian Geologic Evolution

1980

The mean density, 3.933 g/cm 3, and the estimated moment of inertia factor, 0.365, constrain the density distribution within Mars but do not define it uniquely. For plausible core densities, core radii can range from-•1350 to-•2200 km, with the core constituting from-•13 to-•35% of the planet's mass. Possible extremes for the zero-pressure density of the Martian mantle could be as high as-•3.6 g/cm 3 or as low as-•3.3 g/cm 3. The Martian mantle is probably denser than the terrestrial mantle; however, the actual density and composition of the Martian mantle are not well constrained by present data. The dominant Martian lavas are probably marie or ultramarie. Viking lander analyses suggest that soils are hydrated, Fe 3+bearing weathering products of marie rocks. Earth-based reflectance spectra indicate olivine (or basaltic glass) and pyroxene in dark areas and several percent Fe 3+ oxides in bright areas; integral disk spectra indicate the presence of H20 ice and mineral hydrates. Stable weathering products under current surface conditions are primarily oxides and carbonates. Martian surface materials probably consist of variable proportions of made igneous minerals and weathering products; the actual mineralogy is not well constrained by present data. A major geologic dichotomy exists between the complex northern plains and the ancient southern cratered terrain. The Thatsis plateau, which dominates the low-degree harmonics of the gravity field, appears to be only partially compensated; Olympus Mons appears to be completely uncompensated. Substantial stresses must be supported, either statically by a thick, rigid lithosphere, or dynamically. Mean crustal thicknesses ranging from 23 to 40 km have been obtained from modeling of Bouguer gravity data. Lithospheric thicknesses ranging from 25 to 50 km under volcanoes in the Thatsis and Elysium provinces to > 150 km under Olympus Mons have been obtained from consideration of the effects of mass loading by volcanic constructs. Many of the compressional and extensional features on Mars have orientations consistent with formation by fracturing in response to loading by the Thatsis plateau. The deficiency of small craters within cratered terrain is attributed to obliteration by volcanism which formed the intercrater plains in cratered terrain. These intercrater plains, which appear to be the first units formed after the ancient cratered terrain, overlap in relative ages with the ridged plains and the fretted regions; remaining plains units are younger. The maximum resurfacing rate due to volcanism occurred between 1.0 and 1.5 b.y. ago if a constant cratering flux is assumed and between 3.5 and 4.0 b.y. ago if the lunar cratering flux (scaled to Mars) is assumed. Thermal evolution models have considered the formation of initial crust, core formation, mantle differentiation, and planetary radius changes, but not the major geologic asymmetries of Mars. The time scales of thermal evolution models can be lengthened or shortened by making various assumptions about initial temperatures and heat sources. Models in which the core formed in the first billion years and in which the peaks of mantle differentiation, volcanism, and planetary radius occur between 1.5 and 3.5 b.y. ago are consistent with a Martian cratering flux intermediate between the constant flux model and the scaled lunar flux. The high •SN/•nN ratio of the Martian atmosphere, 1.7 times the terrestrial value, is ascribed to mass-dependent loss of 10-150 times the present amount of atmospheric •nN. The absence of observable isotopic effects in C and O suggests that atmospheric CO2 and H20 must exchange periodically with a larger, normally nonatmospheric reservoir. The Martian atmosphere exhibits a 'planetary' type pattern of noble gas abundances, with xenon depleted in relation to the other noble gases. Estimates of the whole planet column abundances of CO2 and H20 range from 290 to 8000 g/cm 2 and from 600 to 1600 g/cm 2, respectively. Amounts of H20 and CO2 which are comparable to or perhaps greatly in excess of the whole planet estimates made on the basis of atmospheric noble gas abundances can be stored in plausible reservoirs: the residual polar caps; hydration, oxidation, and carbonation of surface materials; adsorption and absorption into the regolith; and as subsurface ices. A number of surface features have morphologies which appear to require tens of meters of water, and perhaps more, for their formation: fretted terrain, channels, patterned or polygonal ground, rampart ejecta deposits, and possible table mountains.

The Mantle of Mars: Some Possible Geological Implications of Its High Density

1978

The density of the Martian mantle is estimated to be about 3.55 g/cm 3 (Reasenberg, 1977). Model mineral assemblages for the Martian mantle (at 30 kbar) were calculated using a modified CIPW norm scheme by adding FeO to model terrestrial mantle compositions. The density of the resulting mineral assemblages vary with increasing FeO content. With pyrolite starting compositions for the terrestrial mantle, the resulting model Martian mantle with density of 3.55 g/cm 3 is not garnet-lherzolite like the Earth; rather it is an assemblage properly called oxide-garnet wehrlite : oxide (periclase-wiistite) 2% ; garnet 11~ ; olivine 73% ; clinopyroxene 12~; with no orthopyroxene. Partial melting of such an assemblage would yield iron-rich, ultrabasic lavas, with extremely low viscosities. Specifically, model partial melts, assuming production from the quaternary eutectic (inferred to be near: OpT g4~ cpx43 OXs) yields an ultrabasic (SiO.2, 41 to 44%) picritic alkMi-basaltic melt (norm composition ne 2.5, plag 32, or 2.4, di 20, ol 37, mt 4.4 and ilm, tr), with a computed viscosity of about 12 P at 1200°C. This model for the composition of the Martian surface lavas (derived from geophysical data and petrologic arguments) is in remarkable agreement with a recently published model by Maderazzo and Huguenin (1977) (derived from reflection spectroscopy, experimental and theoretical nmdels h)r weathering in the Martian environment). The result also appears to be consistent with recent interpretations (Rasool arid Le Sergeant, 1977) of Viking atmospheric chemistry results, namely that the Martian crust is potassium poor. There are a number of geological implications which follow, including (1) superfluid lavas may account for some flood and erosional features observed on Mars; (2) the XIlF inorganic chemistry experiment on Vikings 1 and 2 (Baird, 1976) indeed may be measuring compositions approaching primary lavas, contrary to current interpretations which favor a rather mature (weathered) soil; (3) ultrabasic (ferrokimberlitic) ash might be a major constituent of the Martian soil, especially if cosmological models concerning the incorporation of a much volatile material within the early accreting Mars are correct-a matter of current debate; (4) a number of mineral assemblages riot previously considered are possible in the Martian mantle depending principally on the activity of volatile substances, (S, O, C, H) ; it is possible that some very unusual magmas are produced on partial melting; and (5) some fcrro-granite melts might be produced by liquid immiscibility.

A record of igneous evolution in Elysium, a major martian volcanic province

Scientific reports, 2017

A major knowledge gap exists on how eruptive compositions of a single martian volcanic province change over time. Here we seek to fill that gap by assessing the compositional evolution of Elysium, a major martian volcanic province. A unique geochemical signature overlaps with the southeastern flows of this volcano, which provides the context for this study of variability of martian magmatism. The southeastern lava fields of Elysium Planitia show distinct chemistry in the shallow subsurface (down to several decimeters) relative to the rest of the martian mid-to-low latitudes (average crust) and flows in northwest Elysium. By impact crater counting chronology we estimated the age of the southeastern province to be 0.85 ± 0.08 Ga younger than the northwestern fields. This study of the geochemical and temporal differences between the NW and SE Elysium lava fields is the first to demonstrate compositional variation within a single volcanic province on Mars. We interpret the geochemical a...

Magmatic complexity on early Mars as seen through a combination of orbital, in-situ and meteorite data

Lithos, 2016

Until recently, Mars was considered a basalt-covered world, but this vision is evolving thanks to new orbital, in situ and meteorite observations, in particular of rocks of the ancient Noachian period. In this contribution we summarise newly recognised compositional and mineralogical differences between older and more recent rocks, and explore the geodynamic implications of these new findings. For example the MSL rover has discovered abundant felsic rocks close to the landing site coming from the wall of Gale crater ranging from alkali basalt to trachyte. In addition, the recently discovered Martian regolith breccia NWA 7034 (and paired samples) contain many coarse-grained noritic-monzonitic clasts demonstrably Noachian in age, and even some clasts that plot in the mugearite field. Olivine is also conspicuously lacking in these ancient samples, in contrast to later Hesperian rocks. The alkali-suite requires low-degree melting of the Martian mantle at low pressure, whereas the later Hesperian magmatism would appear to be produced by higher mantle temperatures. Various scenarios are proposed to explain these observations, including different styles of magmatic activity (i.e. passive upwelling vs. hotspots). A second petrological suite of increasing interest involves quartzo-feldspathic materials that were first inferred from orbit, in local patches in the southern highlands and in the lower units of Valles Marineris. However, identification of felsic rocks from orbit is limited by the low detectability of feldspar in the near infrared. On the other hand, the MSL rover has described the texture, mineralogy and composition of felsic rocks in Gale crater that are granodiorite-like samples akin to terrestrial TTG (Tonalite-Trondhjemite-Granodiorite suites). These observations, and the low average density of the highlands crust, suggest the early formation of 'continental' crust on Mars, although the details of the geodynamic scenario and the importance of volatiles in their generation are aspects that require further work.

Core Formation and Mantle Differentiation on Mars

Space Science Reviews, 2013

Geochemical investigation of Martian meteorites (SNC meteorites) yields important constraints on the chemical and geodynamical evolution of Mars. These samples may not be representative of the whole of Mars; however, they provide constraints on the early differentiation processes on Mars. The bulk composition of Martian samples implies the presence of a metallic core that formed concurrently as the planet accreted. The strong depletion of highly siderophile elements in the Martian mantle is only possible if Mars had a large scale magma ocean early in its history allowing efficient separation of a metallic melt from molten silicate. The solidification of the magma ocean created chemical heterogeneities whose ancient origin is manifested in the heterogeneous 142 Nd and 182 W abundances observed in different meteorite groups derived from Mars. The isotope anomalies measured in SNC meteorites imply major chemical fractionation within the Martian mantle during the life time of the short-lived isotopes 146 Sm and 182 Hf. The Hf-W data are consistent with very rapid accretion of Mars within a few million years or, alternatively, a more protracted accretion history involving several large impacts and incomplete metal-silicate equilibration during core formation. In contrast to Earth early-formed chemical heterogeneities are still preserved on Mars, albeit slightly modified by mixing processes. The preservation of such ancient chemical differences is only possible if Mars did not undergo efficient whole mantle convection or vigorous plate tectonic style processes after the first few tens of millions of years of its history.