Icarus 200 (2009) 39–51 Contents lists available at ScienceDirect Icarus www.elsevier.com/locate/icarus The morphologies of volcanic landforms at Central Elysium Planitia: Evidence for recent and fluid lavas on Mars J. Vaucher a , D. Baratoux a,∗ , M.J. Toplis a , P. Pinet a , N. Mangold b , K. Kurita c a Observatoire Midi-Pyrénées, Laboratoire Dynamique Terrestre et Planétaire, University Toulouse III, UMR CNRS 5562, Toulouse, France b Laboratoire de Planétologie et Géodynamique, Nantes University, UMR CNRS 6612, Nantes, France c Earthquake Research Institute, Tokyo, Japan article info abstract Article history: Received 18 February 2008 Revised 25 October 2008 Accepted 3 November 2008 Available online 28 November 2008 Keywords: Mars Volcanism This paper focuses on physical parameters (flow rates and rheological properties) of lava flows observed in the Central Elysium Planitia (CEP) region of Mars. The flows are modeled as Newtonian fluids, using the Jeffrey’s equation and the concept of Graetz number, or alternatively as Bingham fluids. In addition to these approaches, a theoretical model of the shape of shield volcanoes based on the solution for the porous flow of an unconfined aquifer is applied to 5 shields, providing independent quantifications of rheological variations between the shields. This analysis indicates that of the five volcanoes studied, two are partially buried by lava postdating their formation, a result which has been confirmed independently in one case by high resolution images. Our observations reveal that two types of lava flows may be found in the CEP region. The first group is composed of large lava flows with viscosities around ∼2.5 × 10 5 Pas or yield strengths ranging from 100 to 500 Pa. The second group includes small lava flows of the shield volcanoes and large leveed lava channels on the plains with viscosities below 10 3 Pa s, or yield strengths less than 200 Pa. When compared with other volcanic regions on Mars investigated with similar approaches, these latter values are, at present, the lowest inferred for martian lava flows. Several hypotheses for the formation of these lavas are discussed in the context of CEP given that low viscosity can be the result of (1) high temperature, (2) low crystal content, (3) low Si abundance of the liquid phase, and/or (4) the presence of dissolved volatiles. Two scenarios are considered. In the first one, it is demonstrated that low viscosity lavas (of low silica content) can be produced in the context proposed by Schumacher and Breuer [Schumacher, S., Breuer, D., 2007. Geophys. Res. Lett. 34. L12202] for recent volcanism. However, geochemical maps derived from GRS measurements do not provide support for anomalously low silica concentrations in this region. In the second scenario, a water-rich magma is proposed, although arguments in favor of a water-rich mantle source below the CEP are not available at the present time.  2009 Elsevier Inc. All rights reserved. 1. Introduction The Central Elysium Planitia (CEP), previously named Cerberus plains, are one of the youngest volcanic provinces at the mar- tian surface (Plescia, 1990). This region is characterized by both long lava flows of low surface roughness and the occurrence of low shield volcanoes (Fuller and Head, 2002; Plescia, 1990, 2003; Berman and Hartmann, 2002; Burr et al., 2002a, 2002b; Keszthelyi et al., 2000, 2004; Sakimoto and Gregg, 2001, 2004; Sakimoto et al., 2003; Werner et al., 2003; Lanagan, 2004; Vaucher et al., 2005). Recent detailed mapping and dating of this area confirm and doc- ument the abundant volcanic activity in this region over the last 200 million years (Vaucher et al., 2008). * Corresponding author. E-mail address: baratoux@dtp.obs-mip.fr (D. Baratoux). The morphologies of these volcanic landforms have been previ- ously used to constrain effusion rates and rheological properties of the CEP lavas, providing insights into the nature of the eruptions. Such studies generally assume or indirectly infer that the viscosity of these lavas was relatively low. For example, Sakimoto and Gregg (2004) calculated lava flow rates assuming viscosity in the range 10 2 to 10 4 Pa s, while Keszthelyi et al. (2000, 2004) found that a viscosity of 10 3 Pas was the most appropriate to explain the for- mation of the platy ridged surface morphology of long sheet flows. Shield volcanoes, on the other hand, have been interpreted to re- sult from eruptions at lower effusion rate and/or lavas of higher viscosity compared to the sheet flows (Sakimoto and Gregg, 2004; Plescia, 2003). However, it remains that despite its importance, the viscosity of these lavas is a poorly known parameter. In this contribution, we aim to constrain the rheology of lavas in the context of both shield volcanoes and large lava flows on the CEP. For the case of lava flows, two end member approxima- 0019-1035/$ – see front matter  2009 Elsevier Inc. All rights reserved. doi:10.1016/j.icarus.2008.11.005