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Nectaris Fossae & Protva Valles

Thaumasia Planum is a large volcanic highland plateau, located south of Melas and Coprates Chasma which are part of the giant Vallis Marineris canyon system. It was named after a classical albedo feature and is made up largely of lava flows, at least several thousand meters thick. The flows date back to the Noachian, the oldest of the three Martian geologic time periods, and are about 4 billion years old. It borders to the east on a 900 km long north to northeast trending ridge, informally named Coprates rise.

The HRSC observation presented here shows the eastern flank of Coprates rise, containing tectonic features of the Nectaris Fossae fractures, as well as fluvial valleys Protova Valles. The topography is indicative of extensive reworking by tectonism and subsequent incision by valley networks. Some landforms on the surface are evidence of lava flows. Numerous wrinkle ridges can be spotted (see annotated image and overview map).

The formation of the Nectaris fossae began sometime in the Noachian and may have continued into the Late Hesperian period. It is believed to have a genetic relationship to the Valles Marineris System. In this HRSC observation, the fractures almost vertically cut through the image and are often filled with light toned dust.

The Protva Valles valley network is considerably degraded and was dated to the Late Noachian/Early Hesperian period, a time when much more water was available as runoff and could shape the surface by erosion.

The evolution of the region could have started with the load caused by the formation of the Tharsis volcanoes which caused stress, resulting in numerous fractures. Then, the region was repeatedly covered by basaltic lava flows. Wrinkle ridges formed as result of regional compression. In a later stage, the region was covered by volcanic ash and dust. Finally, the valleys were carved into the surface. It is unclear, where the waters came from. Some of the valleys appear to be incised deeper into the rock, others are more surficial and broader. They also appear to have their source at different height levels, which could be a hint to groundwater sapping. However, the intense erosion makes it difficult to assess the provenance of the waters. The height differences within this image are breathtaking 4500m! Since the formation of Protva Valles about 3.8 billion years ago, the geology has remained largely unchanged.