Syrtis Major and small highland volcanoes

Syrtis Major Planum (centered at 9.2°N, 67.1°E) is a unique volcano on Mars. Its large (1300km) diameter and low summit height (~2km) give flank slopes of <1°. Lava flow lobes, channels, and tubes are identified on Syrtis Major Planum’s flanks. Intersecting wrinkle ridges, similar to those found on other Martian planitia, cover Syrtis Major Planum as well. A summit caldera complex, consisting of Nili and Meroe Paterae, likely formed from multiple eruptions emptying an underlying magma chamber. Crosscutting and superposition relations observed between lava flows and wrinkle ridges on Syrtis Major Planum’s flanks suggest a complicated history of repeated edifice inflation, volcanic eruption, and subsequent edifice deflation. Silica-rich materials, probably products of hydrothermal alteration, are found within Nili Patera, and ultramafic olivine-rich lavas cover part of Syrtis Major Planum’s slopes. Syrtis Major Planum’s rich and complex volcanic history make it unique on Mars.