Tyrrhena Patera: Geologic history derived from Mars Express High Resolution Stereo Camera

We used Mars Express High Resolution Stereo Camera images of the Tyrrhena Patera volcano to assign cratering model ages to material units defined in the Viking Orbiter-based geologic mapping. Cratering model ages are generally consistent with their stratigraphy. We can identify three key intervals of major activity at Tyrrhena Patera: (1) formation of the volcanic edifice in the Noachian Period, ∼3.7-4.0 Ga, shortly following the Hellas impact (∼4 Ga) and coincident with the formation of Hadriaca Patera (∼3.9 Ga); (2) modification of the edifice and formation of the caldera rille and channels in the Hesperian Period, possibly extending into the Amazonian Period; and (3) a final stage of modification in the Late Amazonian Epoch, ∼0.8-1.4 Ga. Early- to mid-Hesperian activity on Tyrrhena Patera is consistent with similar activity on Hadriaca Patera at ∼3.3-3.7 Ga. The most recent dateable event on Tyrrhena Patera is modification on the upper shield, caldera rille, and channel floors at ∼800 Ma. This coincidence of resurfacing in three units suggests a widespread process(es), which we speculate involved preferential (aeolian?) erosion of small craters on these flatter surfaces relative to the other units on the volcano. Alternatively, some combination of pyroclastic flow emplacement on the upper shield and fluvial activity in the caldera rille and channels, followed by differential aeolian erosion and deposition, could have produced the present surface. Regardless, major geologic resurfacing ended at Tyrrhena Patera nearly a billion years ago.