The rocks of Mars, from far and near

Abstract

Abstract-The age, structure, composition, and petrogenesis of the martian lithosphere have been constrained by spacecraft imagery and remote sensing. How well do martian meteorites conform to expectations derived from this geologic context? Both data sets indicate a thick, extensive igneous crust formed very early in the planet's history. The composition of the ancient crust is predominantly basaltic, possibly andesitic in part, with sediments derived from volcanic rocks. Later plume eruptions produced igneous centers like Tharsis, the composition of which cannot be determined because of spectral obscuration by dust. Martian meteorites (except Allan Hills 84001) are inferred to have come from volcanic flows in Tharsis or Elysium, and thus are not petrologically representative of most ofthe martian surface. Remote-sensing measurements cannot verify the fractional crystallization and assimilation that have been documented in meteorites, but subsurface magmatic processes are consistent with orbital imagery indicating thick crust and large, complex magma chambers beneath Tharsis volcanoes. Meteorite ejection ages are difficult to reconcile with plausible impact histories for Mars, and oversampling of young terrains suggests either that only coherent igneous rocks can survive the ejection process or that older surfaces cannot transmit the required shock waves. The mean density and moment of inertia calculated from spacecraft data are roughly consistent with the proportions and compositions ofmantle and core estimated from martian meteorites. Thermal models predicting the absence of crustal recycling, and the chronology of the planetary magnetic field agree with conclusions from radiogenic isotopes and paleomagnetism in martian meteorites. However, lack of vigorous mantle convection, as inferred from meteorite geochemistry, seems inconsistent with their derivation from the Tharsis or Elysium plumes. Geological and meteoritic data provide conflicting information on the planet's volatile inventory and degassing history, but are apparently being reconciled in favor of a periodically wet Mars. Spacecraft measurements suggesting that rocks have been chemically weathered and have interacted with recycled saline groundwater are confirmed by weathering products and stable isotope fractionations in martian meteorites.

Oxygen fugacity in the Martian mantle controlled by carbon: New constraints from the nakhlite MIL 03346

“…However, much of what we know about the Martian interior comes from studies of Martian meteorites. Some shergottites are basaltic rocks that appear to represent melts of the Martian mantle, whereas lherzolitic shergottites, nakhlites, Chassignites and Allan Hills (ALH) 84001 are most likely cumulate magmatic rocks (McSween 2002). Oxygen fugacity (fO 2 ) recorded in Martian meteorites is variable, and has been attributed to both crustal assimilation processes and mantle source region characteristics (Borg and Draper 2003;Herd 2003;Jones 2003).…”

Noble gases in mineral separates from three shergottites: Shergotty, Zagami, and EETA79001

“…Furthermore, compared to other meteorites and lunar samples, the SNC meteorites differ not only in oxygen isotopes, but also in several other characteristic chemical and isotopic features, e.g., implied oxygen fugacity (see McSween 1984McSween , 1994, and 2002 for a review). In addition, not only does the group include more highly differentiated rock types like basalts, but these are also characterized by young crystallization ages (McSween 1984(McSween , 1994(McSween , 2002Meyer 2003;Nyquist et al 2001).…”

Hydrothermal alteration at the Lonar Lake impact structure, India: Implications for impact cratering on Mars

“…These tholeiitic basalts have lower MgO, higher total iron, lower Al 2 O 3 , and higher CaO content than do other terrestrial tholeiitic provinces (Roy and Chatterjee 1998). The unusual compositional characteristics of the Lonar crater closely match the composition of martian basalts, which also have higher Fe and lower Al abundances than most terrestrial basalts (McSween 1994;McSween 2002) (Fig. 1).…”