Deformed Crater (Tectonized)
A crater that has been partially or completely modified by tectonic process after its formation.
A type of modified crater
Deformed craters typically display anomalous cuts produced by faults or fractures of tectonic and/or volcanic origin.
The degree of deformation varies according to the process causing the deformation and the target region where the crater was formed.
The morphology of the crater will vary depending upon the deformation process. The deformation of craters appears to be restricted to only a fraction of the rocky and icy bodies such as Venus and Ganymede. Deformed craters are assumed to be originally circular. Any deviation from this shape is assumed to be an indication of modification after formation by some sort of tectonic process. For example, impact craters with an elongated cavity suggest extensional forces, whereas a smaller, fractured rim and/or cavity is indicative of shortening due to compressional strain.
Extensional strains of this order can alter preexisting surface features beyond recognition through the process of tectonic resurfacing.
Extensional: Ganymede, Mars, Venus, and Enceladus. Compressional: Mercury.
Mercury: The geometry of deformed craters on Mercury has been used to infer crustal shortening along presumed reverse faults (Pappalardo and Collins 2005). MESSENGER revealed a lunar-like floor-fractured crater. Despite a generally compressive stress regime on Mercury, there are a few occurrences of extension deformation in craters (Head et al. 2009).
Venus: Extensional strain across craters has been estimated by assuming that individual lineaments are normal fault scarps that have deformed the craters they transect (Pappalardo and Collins 2005). Tectonic processes have deformed about 11 % of the Venusian craters (e.g., Balch, Rosa Bonheur) (Ivanov and Head 2011). Matias and Jurdy (2005) found substantial evidence for tectonic disturbance in the northern Beta region. The BAT region includes Venus’ geoid and topographic highs, profuse volcanism, the intersection of three major rifts, and numerous coronae. Furthermore, although BAT covers just 1/6 of the surface, most of Venus’ craters that have been both deformed and embayed (11 out of 19, 58 %) occur here.
Impact craters that show evidence of deformation can be used to locate regional tectonic activity and to estimate relative timing of events.
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