Arabia Terra
Arabia Terra is a large upland region in the north of Mars that lies mostly in the Arabia quadrangle, but a small part is in the Mare Acidalium quadrangle. It is densely cratered and heavily eroded. This battered topography indicates great age, and Arabia Terra is presumed to be one of the oldest terrains on the planet. It covers as much as at its longest extent, centered roughly at with its eastern and southern regions rising above the north-west. Alongside its many craters, canyons wind through the Arabia Terra, many emptying into the large northern lowlands of the planet, which borders Arabia Terra to the north. Features Arabia contains many interesting features. There are some good examples of pedestal craters in the area. A pedestal crater has its ejecta above the surrounding terrain, often forming a steep cliff. The ejecta forms a resistant layer that protects the underlying material from erosion. Mounds and buttes on the floor of some craters display many layers. The layers may have formed by volcanic processes, by wind, or by underwater deposition. Dark slope streaks have been observed in Tikhonravov Basin, a large eroded crater. The streaks appear on steep slopes and change over time. At first they are dark, then turn a lighter color, probably by the deposition of fine, light colored dust from the atmosphere. These streaks are thought to form by dust moving downslope in a way similar to snow avalanches on Earth. Arabia Terra was named in 1879 after a corresponding albedo feature on a map by Giovanni Schiaparelli, who named it in turn after the Arabian peninsula. Possible tectonism Research on the region was undertaken in 1997 and the individuality of the province better defined. An equatorial belt was noted with a crater age distinctly younger than the northern part of the province and of Noachis Terra to the south. This was interpreted as an "incipient back-arc system" provoked by the subduction of Mars lowlands under Arabia Terra during Noachian times. Regional fracture patterns were also explained in this manner, and the rotational instability of the planet as a cause was not supported. It contains extension tectonic features Possible volcanism A 2013 study proposed that a number of craters within Arabia Terra, including Eden Patera, Euphrates Patera, Siloe Patera, and possibly Semeykin crater, Ismenia Patera, Oxus Patera and Oxus Cavus, represent calderas formed by massive explosive volcanic eruptions (supervolcanoes) of Late Noachian to Early Hesperian age. Termed "plains-style caldera complexes", these very low relief volcanic features appear to be older than the large Hesperian-age shield volcanoes of Tharsis or Elysium. Eden Patera, for example, is an irregular, 55 by 85 km depression up to 1.8 km deep, surrounded by ridged basaltic plains. It contains three linked interior depressions, demarcated by arcuate scarps, that have terraces suggestive of lava lake drainage and faults suggestive of collapse. The features indicative of impact origin that would be expected in an impact crater of comparable diameter and depth are absent. The authors regard crustal