Mineralogy of recent volcanic plains in the Tharsis region, Mars, and implications for platy-ridged flow composition.
Résumé
Volcanism on Mars occurred until recently, but the mineralogy of recent lava plains is poorly known because few regions display fresh outcrops devoid of dust. Using visible and near infrared data of the Mars Express probe, two new volcanic plains in Noctis Labyrinthus have been identified, and the existence of a volcanic plain on the floor of Echus Chasma has been confirmed. Crater retention ages estimated for these three plains range between 50 and 100 My, corresponding to the Late Amazonian. These plains represent an excellent opportunity to constrain the mineralogy of recent volcanic rocks. Results show that basaltic compositions with plagioclase and high calcium pyroxene are predominant. The low olivine proportion suggests that the apparent fluidity of these flat plains is not related to magmas being ultramafic. In addition, a platy-ridged texture is observed in two of the studied regions. Our study shows, for the first time, that this texture is associated with volcanic rocks, and that these rocks are of typical basaltic mineralogy. Finally, these volcanic plains are located more than 1000 km east of previously known late Amazonian volcanic centers of the Tharsis region, an observation to be taken into account when considering models of recent volcanism on Mars. (C) 2009 Elsevier BM. All rights reserved.