astrobleme


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astrobleme

astrobleme (ăsˈtrōblēmˌ), 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.
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astrobleme

[′as·trō‚blēm]
(geology)
A circular-shaped depression on the earth's surface produced by the impact of a cosmic body.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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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)
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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