A description of surface features in north Tyrrhena Terra, Mars: evidence for extension and lava flooding

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Journal Article
Icarus, 2007, 191 (2), pp. 524 - 544
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We studied north Tyrrhena Terra, an approxinmatley 39,000 km2 area, located in the transition region straddling the Amenthes and Mare Tyrrhenum Mars Chart quadrangles 14 and 22, respectively. The study area comprises ancient terrains with infilled craters, ridges and valleys. Interpretation of orbiter data of ancient terrains is inherently difficult, but valuable information can be obtained using multiple dataseets and analysing various geological features. Using data from the high resolution stereo Camera on board Mars Express, complemented by Mars Global Surveyor MOLA DEM and MOC Narrow Angle datasets, we observed and interpreted surface morphologies at a scale suitable for geologic investigation. Morphometric examination of a 31 km diameter large impact crater indicated that tectonism and volcanism were responsible for its morphologic modification. Small impact crater depth/diameter relationships inidctaed that smooth surfaces of valleys are composed of highly consolidfated material. Surface cracks and lobate fronts further suggested that the rocks are volcanic. Examiantion of tectonic features revealed that in the study area: a dominant NW-SE fabric is related to a ridge/bench-scarp-valley repition consistent with synthetic and antithetic normal faulting: a NNW-SSE linement represents the surface expression of normal faulting post-dating all other tectonic features. A weak NE-SW fabric is observable as small sublinear depressions and at the contact between units internal to one large crater. One 20 km diameter crater is the study area was interpreted to be a caldera infilled by thick volcanic rock layers. Identification of wrinkle ridges further indicated that thick layered lava flows infilled the main depression of the study area. The available evidence suggests that the study area underwent multiple episodes of extension and volcanism.
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