References Hhh
Aassoumi H, Broutin J, El Wartiti FP, Koeniguer J, Quesada C, Simancas F, Toutin-Morin N 1992 Pedological nodules with cone in cone structure in the Permian of Sierra Morena Spain and central Morocco. Carbonates and Evaporites 7 140-149 Albat HM, Mayer JJ 1990 Shatter cones in Vredefort rocks - imagination or reality South African Journal of Geology 93 547-548 Amstutz GC 1965 A morphological comparison of diagenetic cone-in-cone structures and shatter cones. Annals of the New York Academy of...
Earlier Studies and the Formation of Polygonal Craters
Theories of the origin of hexagonal lunar craters were discussed already in 1908 by Puiseux Fielder 1961 Kopal 1966 . The 1960's, however, seems to have been the golden age of polygonal crater studies. Gilbert Fielder, a strong advocate of the lunar craters' volcanic origin, fundamentally stated that polygonally shaped craters are common Fielder 1961 . Later Fielder also noted the connection between square-shaped and hexagonal craters with orthogonal and three-directional fracturing,...
Pseudotachylites in Large Impact Structures
Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, P.O. Wits 2050, Johannesburg, South Africa reimoldw geosciences.wits.ac.za gibsonr geosciences.wits.ac.za Abstract. The catastrophic processes associated with meteorite impact are capable of producing dark-matrix breccias by a variety of mechanisms during both the shock compression and crater modification phases. Distinguishing the origins of these breccias provides vital clues to...
Pseudotachylite or Pseudotachylitic Breccia Comparison of
In this section, a number of aspects of breccias occurring in the Vredefort Dome-Witwatersrand Basin VWB and in tectonic fault shear zone TFS settings are compared. Pseudotachylitic breccias in the Vredefort Dome -Witwatersrand Basin can be divided into two groups 1. the breccias in the goldfields gt 80 km from the center of the structure and well outside the zone of shock metamorphism 2. the breccias in the Vredefort dome, where shock-induced features like shatter cones, PDFs and coesite and...
Origin of ConeinCone Structures
The origin of cone-in-cone structures has been strongly debated, but many aspects of their formation have remained unclear. A common definition Bates and Jackson 1987 states The structure appears to be due to pressure aided by crystallization and weathering solution along intersecting conical shear zones. The important hypotheses for the formation of calcareous cone-in-cone structures can be divided into two groups those favoring early displacive formation of concretions in soft sediment and...
Contents
Pseudotachylites in Large Impact Structures Wolf U. Remold and Roger L. The Mechanics of Pseudotachylite Formation in Impact Events H. Jay Silicified Cone-in-Cone Structures from Erfoud Morocco A Comparison with Impact-Generated Shatter Cones Stefano Lugli, Wolf U. Remold and Christian Koeberl 81 Redisribution of Lithologies in Impact-induced Dikes of Impact Structures Victor L. The Preliminary Analysis of Polygonal Impact Craters within Greater Hellas Region, Mars Teemu Ohman, Marko Aittola,...
The Setting of Pseudotachylitic Breccia in Impact Craters
Veins of dark-matrix breccia resembling tectonic pseudotachylite have been described from many impact structures - generally from crater floor rocks, but occasionally from crater rim settings. Such reports are very rare for small, simple bowl-shape craters, and it must be questioned whether any bona fide pseudotachylite friction melt has ever been described from these. For example, the only breccia ever recovered from the crater rim of the Tswaing Pretoria Saltpan meteorite crater that...
List of contributors
Geological Survey of Sweden Division of Geophysics Box 670 S-751 28 Uppsala, Sweden sven.aaro sgu.se Department of Land and Water Resources Engineering Royal Institute of Technology S-100 44 Stockholm, Sweden annb kth.se Department of Geology and Geochemistry Stockholm University S-10691 Stockholm, Sweden ilka geo.su.se Raymond A. Donelick Apatite to Zircon Inc. 1075 Matson Road Viola, ID 83872-9709, USA Laboratory of Palaeobotany and Palynology Utrecht University Budapestlaan 4 Department of...
Shatter Cone Formation
Different mechanisms have been proposed for the formation of shatter cones. This includes the idea by Johnson and Talbot 1969 that the elastic precursor of a shock front is scattered by a heterogeneity in a rock see also Sharpton et al. 1996 . Gash 1971 proposed that shatter cones were produced from the interaction of an incident shock wave with a tensile wave reflected from a reflective source such as a local heterogeneity in a rock for example a relatively large grain, pore space, or fracture...
Shattercone like Phenomena
Abundance of shatter cones certainly seems to be diagnostic of impact. However, cone fractures of amazing similarity to impact produced shatter cones have been described from fossil water-falls Reimold and Minnitt 1999 in the eastern Transvaal Mpumalanga Province of South Africa and from a location in the southeastern collar of the Vredefort Dome, and from southern Botswana. These percussion marks may comprise complete or major segments of circular fractures up to 360 degree features were...
The Mechanics of Pseudotachylite Formation in Impact Events
Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, U.S.A. jmelosh lpl.arizona.edu Abstract. This paper presents a discussion of the basic constraints controlling the formation of pseudotachylites in the rapidly sheared rocks in the vicinity of a large meteorite impact. The prevailing opinion among many geologists is that pseudotachylites are formed by friction melting of rocks and or shearing associated with differential shock compression of adjacent rock types. Several...
Silicified ConeinCone Structures from Erfoud Morocco A Comparison with
Stefano Lugli Wolf U. Reimold 2 and Christian Koeberl 3 'Dipartimento di Scienze della Terra, Universit degli Studi di Modena e Reggio Emilia, Largo S. Eufemia 19, 41100 Modena, Italy lugli.stefano unimore.it 2Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, P.O. Wits 2050, Johannesburg, South Africa reimoldw geosciences.wits.ac.za 3Department of Geological Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria...