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Name

AZUARA

StatusProven
Country Spain
CoordinatesLat. N 41°10' Long.W 0°55'
Diameter km 30.0
Age Ma or date 23 - 41
Synonyms
Remarks There has been lots of depate is Azuara an impact structure or do it has terrestrial origin (Cortés 2002). Indications of shock pressures like PDFs in quartz has been described to be found in samples from Azuara. Measured directions of these PDFs suggest clearly impact origin. In addition to PDFs also diaplectic glass has been reported from Azuara (Ernstson 2002).

However, some other TEM investigations have not confirm PDFs in some Azuara samples (Lagenhorst 1996a, Cortés 2002), but those samples have been from outside the structure. It is also claimed that some shockmetamophic evidences from Azuara structure are not well presented (French 2010) but that will apply also for many other proven impact structures. There is more about the discussion in online article (Impact-structures.com B).

I have had some hard time to decide my mind with Azuara and it has spend some times on my list of canditates lately. But to be honest, there is several other structures on my main list, which are listed in other major impact structure lists on the net, and which should be on the list of canditate structures instead of Azuara.

See Wikipedia for more detailed information.

Paleontological evidences points to age of Upper Eocene - Oligocene epoch (approx. 23-41 Ma). Ages less than 130 Ma and about 40 Ma has been suggested.
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References
Cortés 2002 Cortés A.L., Diaz-Martínez E., Sanz-Rubio E., Martínez-Frías J. and Fernández C., ''Cosmic impact versus terrestrial origin of the Azuara structure (Spain): A review'', MAPS 37 (2002)
Ernstson 1985 Ernstson K., Hamman W., Fiebag J. & Graup G., Earth Planet.Sci.Let., 74 (1985)
Ernstson 1987 Ernstson K., Feld H., and Fiebag J., Meteoritics 22 (1987)
Ernstson 1990 Ernstson K. and Claudin, F., N.Jb.Geol.Paläont.Mh. (1990)
Ernstson 1992 Ernstson K. and Fiebag, J., Geol.Rundschau, 81/2 (1992)
Ernstson 2002 Ernstson K., Claudin F., Schüssler U. and Hradil K., "The mid-Tertiary Azuara and Rubielos de la Cérida paired impact structures (Spain)", Treballs del Museu de Geologia de Barcelona, Núm 11, Separata (2002)
French 2010 French B.M., and Koeberl C.,"The convincing identification of terrestrial meteorite impact structures: What works, what doesn't, and why", Earth-Science Reviews, Volume 98, Issues 1-2, 1 January 2010, Pages 123-170 (2010)
Hodge 1994 Hodge, Paul W., ''Meteorite craters and impact structures of the Earth'', book, 122 pp, Cambridge University Press (1994)
Impact-structures.com "Ernstson Claudin Impact Structures" website. (checked 16 Feb 2010)
Impact-structures.com B "Shock effects (shock metamorphism) in rocks from the Azuara impact structure", an online article in Ernstson Claudin Impact Structures webpage (checked 6 March 2010)
Lagenhorst 1996a Lagenhorst F. and Deutsch A., "The Azuara and Rubielos Structures, Spain: Twin Impact Craters or Alpine Thrust Systems? TEM Investigations on Deformed Quartz Disprove Shock Origin", XXVII LPSC, Abstract 1363, Lunar and Planetary Institute (1996)
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