The volcanic and thermal history of Mars

Details The volcanic and thermal history of Mars The volcanic and thermal history of Mars

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p14a..05b&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P14A-05

Mathematics

Logic

[5410] Planetary Sciences: Solid Surface Planets / Composition, [5480] Planetary Sciences: Solid Surface Planets / Volcanism, [6225] Planetary Sciences: Solar System Objects / Mars

Scientific paper

Reconstruction of the geological history of Mars has been the focus of considerable attention over the past four decades, with important discoveries being made concerning variations in surface conditions. On the other hand, despite a significant increase in the amount of data related to the morphology, mineralogy and chemistry of the martian surface, there is no clear global picture of how magmatism has evolved over time and how these changes relate to the thermal evolution of the planet. With this in mind we have used Silica, Iron, and Thorium global maps from the data Gamma Ray Spectrometer (GRS) onboard the Mars Odyssey spacecraft, focusing on 12 major volcanic provinces of variable age. All three elements show significant variability and a prominent anticorrelation is observed between SiO2 and thorium, with younger volcanoes being characterized by lower SiO2 and higher thorium contents. Values of FeO are generally lower for the younger edifices of the Tharsis dome. Assuming that melts are produced by adiabatic decompression of the martian mantle associated with convective upwelling and that liquids equilibrate with the mantle at a single pressure and temperature at the base of the lithosphere, the chemical variations are found to be consistent with varying degrees of melting of the mantle. In detail, there is evidence for thickening of the lithosphere (17-25 km/Gy) associated with a decrease of mantle potential temperature over time (30-40 K/Gy). This cooling rate is consistent with simple models of convection, and contrasts with the higher cooling rate for the Earth over the last 3.5 Gyr (70-100°C/Gyr). This comparison suggests that the terrestrial value is the result of some specific feature of the Earth, such as a prolonged period of plate tectonics, or the possible existence of a deep magma ocean that concentrated radiogenic elements. The evolution with time of the chemical composition of primary melts has consequences for the melt rheology during ascent and emplacement and for the nature and proportion of minerals in exposed volcanic rocks. Our results offer a useful frame for understanding the diversity of volcanic landforms and the variable proportions of pyroxene, olivine and plagioclase in igneous rocks revealed by visible and near-infrared observations. Overall, a self-consistent picture of the thermal evolution of Mars emerges and provides a useful reference for planetary evolution.

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