The morphologies of volcanic landforms at Central Elysium Planitia: Evidence for recent and fluid lavas on Mars

Abstract

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 Pa s 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.