astrobleme


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astrobleme

(ăs`trōblēm'), large, circular structure ranging from c. 1-2 mi to 40 mi (.8–64 km) in diameter. Astroblemes are found at numerous places on the earth's surface, e.g., Meteor, or Barringer, Crater in Arizona, Brent Crater in Ontario, and Vredefort Ring in South Africa. The presence of meteor fragments, strange conical fracture patterns (called shatter cones), and coesite (a superdense, high-pressure form of quartz) in the rocks at astroblemes suggest an impact, rather than volcanic, origin to these circular structures.

astrobleme

[′as·trō‚blēm]
(geology)
A circular-shaped depression on the earth's surface produced by the impact of a cosmic body.
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For instance, Gravbeg-1 (Sweden) and Vorotilov (Russia) boreholes were drilled within astroblemes, i.e.
Some properties and structure of the crystalline crust from superdeep drilling data (SG-3, SG-4, KTB)
(Les meteorites de plus de 500 tonnes he sont significativement pas ralenties par l'atmosphere terrestre et arrivent au sol avec quasiment la vitesse initiale), laissant une structure circulaire de 180 km de diametre (astrobleme), decouverte il y a 15 ans, (la structure est entouree d'un anneau beaucoup plus tenu de 300 km de diam6tre).
En effet, les geologues qui faisaient des forages en mer de Barents ont trouve le plus grand astrobleme d'Europe, date de 150 M.a.
Mots cles: geomagnetisme, astroblemes, tectites, inversion de polarite.
Impacts meteoriques et changements climatiques
and Suk, M.: 1997, On the existence of the "Sevetin astrobleme", South Bohemia, Czech Republic, Krystalinikum, 23, 83-94.
Ti-rich granodiorite porphyries from the northeastern margin of the Klenov massif (Moldanubian Zone of the Bohemian Massif)
Even after the famous 1980 article by Nobel laureate Luis Alvarez and colleagues, which identified a chemical signal of extraterrestrial origin in the last few centimeters of Cretaceous strata, the Yucatan site was initially overlooked in the otherwise frenzied worldwide search for a corresponding "astrobleme" (literally, "star wound").
Rogue Asteroids and Doomsday Comets: The Search for the Million Megaton Menace That Threatens Life on Earth

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