The Circum-Hellas Province

The Circum-Hellas Volcanic Province includes two large expanses of ridged plains that each include distinct eruptive centers: Hadriacus and Tyrrhenus Montes are located northeast of Hellas in Hesperia Planum, and Amphitrites, Malea, Peneus, and Pityusa Paterae are found in Malea Planum to the south. These volcanoes show low relief forms and degraded surfaces and represent the oldest class of volcanoes on Mars. Hadriacus and Tyrrhenus Montes, the best imaged of the highland paterae, are attributed to layered pyroclastic flow deposits dissected by fluvial erosion and/or groundwater sapping. Amphitrites Patera exhibits similar surface morphology, but Malea, Peneus, and Pityusa Paterae show caldera-like depression without related edifices. Ages of volcanic features in the Circum-Hellas Volcanic Province are commonly Late Noachian or Early Hesperian, but volcanism associated with Tyrrhenus Mons extends into the Late Hesperian/Early Amazonian with emplacement of a large flow field to the southwest along the regional slope toward Hellas.