Aorounga - Hypervelocity Impact Crater

Alternate Names
Local Language
Coordinates 19° 5' 36" N; 19° 14' 34" E
Notes
  1. Located in Northern Chad, 110 km SE of the Emi Koussi volcano in the Tibesti Massif.
Country Chad
Region Borkou
Date Confirmed 1992
Notes
  1. Though first proposed to be an impact crater by (Roland, 1976) the theory at the time was this structure was a granite diapir. It was not until 1992 during a French expedition that evidence for an impact event was found in the form of shatter cones and \"shock-affected quartz\" [PDFs] (Becq-Giraudon et al., 1992).
Buried? No
Drilled? No
Target Type Sedimentary
Sub-Type Sandstone
Apparent Crater Diameter (km) 16 km
Age (Ma) 0.0035 - 383
Notes :
  1. Minimum age: Poorly constrained Maximum age: Late Devonian (~383 Ma) target rock (Wacrenier et al., 1958, according to Koeberl et al., 2005) Previous age constraints: 3.5-12 ka determined by 14C (Becq-Giraudon et al., 1992), apparently incorrect when compared to significantly eroded morphology (Koeberl et al., 2005) 0.5-1 Ma determined by thermoluminescence and electron spin resonance dating of quartz (Maiallier et al., 1997)0.5 Ma determined by cosmogenic nuclide exposure dating (Bourles et al., 1995)

Method :
  1. Stratigraphy
Impactor Type Unknown

Advanced Data Fields

Notes

Erosion
6
  1. Deeply eroded structure.
Final Rim Diameter
Unknown
Apparent Rim Diameter
16 km
  1. (Koeberl et al., 2005)
Rim Reliability Index
3
  1. Nearly circular and has a slightly ecentric central uplift. The outer ring wall separated from the inner ring by depression of uniform width. Both walls rise ~100 m above the mean level of surrounding plain (Becq-Giraudon et al., 1992). \"Figure 5d illustrates two elevation profiles along the N-Sand E-W lines across the crater structure and its environs. The profiles define significant relief of up to 230 m. A central complex of 7.5–8 km in width also contains a central peak of 2–2.5 km in diameter\" (Koeberl et al., 2005). Based on a cross-section of elevation, the height of the central uplift above the floor around it is on the order of 100m. This is interpreted from (Koeberl et al., 2005).
Crater Morphology
Complex
Central Uplift Diameter
1.5km
Central Uplift Height
~1
Uplift Reliability Index
3
Structural Uplift
Unknown
Thickness of Seds
Target Age
Palaeozoic
Marine
No
Impactor Type
Other Shock Metamorphism
Shatter Cones
No
  1. Occurence of \"probable\" shatter cones (Becq-Giraudon et al., 1992); the photographs of these features in (Becq-Giraudon et al., 1992) are not really convincing. Similar features are presented in (Koeberl et al., 2005), it seems that the observed features are ventifacts and not shatter cones.
Planar Fractures
No
Planar Deformation Features
Yes
  1. PDF in quartz grains (Becq-Giraudon et al., 1992).
Diaplectic Glass
No
Coesite
No
Stisovite
No
Crater Fill
LB
  1. (Becq-Giraudon et al., 1992) describes breccias consisting of a coarse-grained siliceous matrix with fine-grained, beige clasts (cm- to dm-size) with fluidal texture, found on top of the inner rim wall (Koeberl et al., 2005).
Proximal Ejecta
Distal Ejecta
Dykes
Volume of Melt
Depth of Melting

References

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N W Roland (1976) Die Ringstruktur Aorounga (Borkou, Sued-Sahara), Geologisches Jahrbuch(33), p. 117-131

R A F Grieve, C A Wood, James B Garvin, G McLaughlin, J F McHone (1988) Possible Impact Craters, Astronaut's Guide to Terrestrial Impact Craters, p. 75, url

J-F Becq-Giraudon, O Rouzeau, E Goachet, S Solages (1992) Meteoritic impact origin of the annular depression of Aorounga, Chad (Africa), Comptes Rendus de l'Academie des Sciences 315, p. 83-88, url

J-F Becq-Giraudon, O Rouzeau, E Goachet, S Solages (1992) Impact hyperveloce d'une meteorite geante a l'origine de la depression circulaire d'Aorounga au Tchad (Afrique), Comptes Rendus de l'Academie des Sciences, Serie 2, Mecanique, Physique, Chimie, Sciences de l'univers, Sciences de la Terre 315(1), p. 83-88, url

C Koeberl (1994) African meteorite impact craters: characteristics and geological importance, Journal of African Earth Sciences 18(4), p. 263-295, doi:10.1016/0899-5362(94)90068-X

N Trenc (1997) Remote sensing analysis of terrestrial meteoritic impact craters using Space Shuttle and other sensors, Department of Geology, TCU Master Thesis, p. 59, url

C Koeberl, W U Reimold, P M Vincent, D Brandt (1998) Aorounga and Gweni Fada impact structures, Chad, Central Africa: petrology and geochemistry of target rocks, Abstracts: Lunar and Planetary Science Conference 29, p. 1103(1-2), Houston, TX, United States (USA): Lunar and Planetary Science Conference, Houston, TX, url

C Koeberl, W U Reimold, G R J Cooper, D R Cowan, P M Vincent (2005) Aorounga and Gweni Fada impact structures, Chad: Remote sensing, petrography, and geochemistry of target rocks, Meteoritics & Planetary Science 40(9-10), U Riller, Wolf Uwe Reimold (ed.), p. 1455-1471, Fayetteville, AR, United States (USA): Meteoritical Society, Fayetteville, AR, url