Gweni-Fada - Hypervelocity Impact Crater

Alternate Names
Local Language
Coordinates 17° 25' 15" N; 21° 44' 60" E
Notes
  1. 30 km NE of Fada.
Country Chad
Region Ennedi
Date Confirmed 1996
Notes
  1. Confirmed by several sets of planar deformation features in quartz grains of the central zone (Vincent and Beauvilian, 1996).
Buried? No
Drilled? No
Target Type Sedimentary
Notes
  1. Structure is exposed in Upper Devonian sandstones and Precambrian basement was not found in central uplift. Lithologies include quarzite, hematite-stained sandstone, pebbly sandstone, and quartz conglomerate (Koeberl et al., 1998).
Sub-Type Sandstone
Apparent Crater Diameter (km) 22 km
Age (Ma) ≤383
Notes :
  1. Age of target rocks and stratigraphic constraints gives a rough, poorly constrained age of ≤383 Ma (Vincent and Beauvilian, 1996) (Koeberl, 2005).

Method :
  1. Stratigraphy
Impactor Type Unknown

Advanced Data Fields

Notes

Erosion
6
  1. No allochthonous lithologies preserved. Crater floor exposed (Koeberl et al., 2005).
Final Rim Diameter
Unknown
Apparent Rim Diameter
22 km
  1. (Korberl et al., 2005) re-assess the diameter as 22km, based on structural info from remote sensing. Minimum diameter of 14 km, (Vincent and Beauvilain, 1996).
Rim Reliability Index
2
  1. Central peak in complex central zone. The external depression is very irregular, with the form of a crescent encircling the central zone on two thirds of its periphery. P.1461 of (Koeberl et al., 2005) about this crater and Aorunga includes elevation profiles along two axes. Central uplift height measured from this, but this is an estimate. Also: "Maximum elevation in [the central uplift] terrain reaches 200m above the ring basin." (Koeberl et al., 2005). "The heart of the structure is the most distorted part. All the benches have dips between 40 ° and the vertical. They are composed of more or less coarse sandstone, sometimes with quartz dragees. Harlania were found in three deposits. These fossils are known in Ennedi under the Spyrophyton sandstones, from the formations attributed to the Lower Devonian to the Ordovician." [Translated by Google from French] (Vincent and Beauvilain, 1996).
Crater Morphology
Complex
Central Uplift Diameter
9km
Central Uplift Height
~0.200
Uplift Reliability Index
3
Structural Uplift
Unknown
Thickness of Seds
Target Age
Palaeozoic
Marine
No
Impactor Type
Other Shock Metamorphism
No
Shatter Cones
No
Planar Fractures
No
Planar Deformation Features
Yes
  1. Single or multiple sets of PDFs with 2 sets of PDFs most common (Koeberl et al., 1998). PDF in quartz (Vincent and Beauvilain, 1996).
Diaplectic Glass
No
Coesite
No
Stisovite
No
Crater Fill
LB
  1. Needs data All samples represent target rocks, some of which have been brecciated (monomict breccia). Most of our samples show evidence of shock metamorphism in the form of PFs as well as PDFs inquartz grains. (Koeberl et al., 2005). No melt rocks or clasts, which might have been used in radiometric dating, were found in any of our samples. Both structures are well exposed in the field and should become subject of detailed ground-based investigations. (Koeberl et al., 2005)
Proximal Ejecta
Distal Ejecta
Dykes
Volume of Melt
Depth of Melting

References

Spot a missing reference? Submit Reference

P M Vincent, A Beauvilain (1996) Decouverte d'un nouveau cratere d'impact meteoritique en Afrique; l'astrobleme de Gweni-Fada (Ennedi, Sahara du Tchad), Comptes Rendus de l'Academie des Sciences, Serie II. Sciences de la Terre et des Planetes 323(12), p. 987-997, Gauthier-Villars, Montrouge

P M Vincent, A Beauvilain (1996) Gweni-Fada (Ennedi, Sahara du Tchad): Un nouvel astrobleme africain, Reunion Annuelle des Sciences de la Terre 7, p. 4, Societe Geologique de France, Paris

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 of Papers Submitted to the 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