Encyclopedia of Planetary Landforms

2015 Edition
| Editors: Henrik Hargitai, Ákos Kereszturi

Deformed Crater (Tectonized)

  • Audeliz Matias
  • Donna M. Jurdy
Reference work entry
DOI: https://doi.org/10.1007/978-1-4614-3134-3_154

Definition

A crater that has been partially or completely modified by tectonic process after its formation.

Category

A type of  modified crater

Synonyms

Description

Deformed craters typically display anomalous cuts produced by faults or fractures of tectonic and/or volcanic origin.

Interpretation

The degree of deformation varies according to the process causing the deformation and the target region where the crater was formed.

Formation

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.

Degradation

Extensional strains of this order can alter preexisting surface features beyond recognition through the process of tectonic resurfacing.

Studied Locations

Extensional: Ganymede, Mars, Venus, and Enceladus. Compressional: Mercury.

Prominent Examples

Balch (Fig. 1), on Venus, serves as an excellent and often-displayed example of Venus’ tectonic activity. This crater has been cut in half by Devana Chasma; thus it predates the tectonic activity in the rift. Basilevsky and Head (2002) argued that Balch does not show evidence of dark parabolas associated with the youngest impact crater on this planet. Based on their estimation, Balch dates to the earliest half of the age of Venus’ surface, extending back 100s of millions of years in the region (Matias and Jurdy 2005).
Deformed Crater (Tectonized), Fig. 1

Balch crater (previously called Somerville crater) (30°N, 282°E, D = 40 km) in Devana Chasma on Venus. Magellan C1-MIDR 30 N279;1,framelet 30 (NASA/JPL)

Regional Variations

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.

Mars: (Fig. 2) On Mars, the ellipticity of craters has been used to infer the total extensional strain across the craters as well as the strain represented by individual faults (Pappalardo and Collins 2005).
Deformed Crater (Tectonized), Fig. 2

Martian crater split up by a fracture of the Sirenum Fossae system, southwest of the Tharsis region (29.7° S, 211.7° E, D = 22 km). Scale bar 5 km. THEMIS V07658005 (NASA/JPL/ASU)

Ganymede (strained crater) (Fig. 3): Five elliptical craters identified in high-resolution images that are transected by sets of subparallel ridges and troughs terrain (rift zone,  groove, Ganymede), interpreted as domino-style normal fault blocks, oriented roughly orthogonal to the long axis of the crater (Pappalardo and Collins 2005). Crater distortion is about 5–50 %. Extensional strains elongated craters near perpendicular to subparallel ridges and troughs. Some are also deformed by distributed simple shear parallel to these tectonic structures. Some craters show tectonic focusing: fractures run through their centers, or differently oriented fractures intersect at the crater center (Prockter et al. 2000) due to possible reactivation of impact-related radial fractures (Figueredo et al. 1999).
Deformed Crater (Tectonized), Fig. 3

Deformed craters at Anshar Sulcus. Scale bar 20 km. Galileo Orbit G8 Mosaic G8GSANSHAR01 (NASA/JPL/ASU)

Moon: Schultz (1976) first identified floor-fractured craters (FFC) using Apollo data. These craters feature shallow floors with fractures, either concentric or polygonal. Combining LOLA and LROC data for improved resolution of FFC, Joziak et al. (2012) test alternative models for formation. They conclude that shallow sill intrusion best fits observations and reject formation by viscous relaxation as a mechanism for FFC (Fig. 4).
Deformed Crater (Tectonized), Fig. 4

Saltu crater (left) in Nicholson Regio scale bar 50 km. Galileo Orbit G7 Mosaic G7GSNICHOL01. (NASA/JPL/ASU)

Significance

Impact craters that show evidence of deformation can be used to locate regional tectonic activity and to estimate relative timing of events.

Similar Landforms

 Elliptical crater,  elliptical crater (oblique impact), and deformed  ring-mold craters

See Also

References

  1. Basilevsky AT, Head JW (2002) Venus: Analysis of the degree of impact crater deposit degradation and assessment of its use for dating geological units and features. J Geophys Res 107:5061. doi:10.1029/2001JE001584CrossRefGoogle Scholar
  2. Figueredo PH, Greeley R, the Galileo SSI team (1999) Fracture patterns on Ganymede and the initiation of tectonic resurfacing. Lunar Planet Sci XXX, abstract #1832, HoustonGoogle Scholar
  3. Head JW, Mruchie SL, Prockter LM, Solomon SC, Strom RG, Chapman CR, Watters TR, Blewett DT, Gillis-Davis JJ, Fassett CI, Dickson JL, Hurwitz DM, Ostrach LR (2009) Evidence for intrusive activity on Mercury from the first MESSENGER flyby. Earth Planet Sci Lett 285:251–262CrossRefGoogle Scholar
  4. Ivanov MA, Head JW (2011) Global geological map of Venus. Planet Space Sci 59:1559–1600CrossRefGoogle Scholar
  5. Joziak LM, Head JW, Zuber MT, Smith DE, Neumann GA (2012) Lunar floor-fractured craters: classification, distribution, origin and implications for magmatism and shallow crustal structure. J Geophys Res 117:E11005. doi:10.1029/2012JE004134CrossRefGoogle Scholar
  6. Matias A, Jurdy DM (2005) Impact craters as indicators of tectonic and volcanic activity in the Beta-Atla-Themis region, Venus. In: Foulger GR, Natland JH, Presnall DC, Anderson DL (eds) Plates, plumes, and paradigms, Geological Society of America special paper 388. Geological Society of America, Boulder, pp 825–839Google Scholar
  7. Pappalardo RT, Collins GC (2005) Strained craters on Ganymede. J Struct Geol 27:827–838CrossRefGoogle Scholar
  8. Prockter LM, Figueredo PH, Pappalardo RT, Head JW III, Collins GC (2000) Geology and mapping of dark terrain on Ganymede and implications for grooved terrain formation. J Geophys Res 105(E9):22519–22540CrossRefGoogle Scholar
  9. Schultz PH (1976) Floor-fractured lunar craters. Moon 15:241–273Google Scholar

Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  1. 1.Center for Distance LearningSUNY Empire State CollegeSaratoga SpringsUSA
  2. 2.Earth and Planetary SciencesNorthwestern UniversityEvanstonUSA