L’évolution volcanique et dynamique de Mars

Thermal and Volcanic History of Mars Reconstruction of the geological history of Mars is focus of considerable attention, with significative 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. This analysis reveals trends in chemical composition which are consistent with varying degrees of melting of the Martian 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 evolution with time of the chemical composition of primary melts have consequences both for the viscosity of ascending magmas 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. In contrast to the Earth, the thermal history is consistent with simple models of mantle convection and provides a useful reference for planetary evolution. En savoir plus : http://www.irap.omp.eu/index.php/actus/volcans-mars Détails de l'évènement : http://spacecampus-paris.eu/index.php?option=com_content&view=article&id=190%3A09092011-seminaire-qlevolution-volcanique-et-dynamique-de-marsq-par-david-baratoux&catid=37&Itemid=74&lang=fr