Clastbearing Dikes Formed by Injection
The most widespread group of injected dikes forms at the excavation stage during the transient cavity growth and radial tension of its floor. In the true crater floor two varieties of such dikes may be distinguished a DI -impactite dikes impact melt matrix , and, 2 DM - mylolisthenite from Greek myle - mill, and olistainein - to slide, Rondot 1994 and polymict lithic breccia dikes matrix composed of clastic material, which is fluidal in the case of mylolisthenite , but some transitional types...
Problematics
On the basis of what we now know about pseudotachylitic breccias in impact structures, in comparison to tectonic pseudotachylite, a number of important unresolved problematics, A - H, can be listed A. The need to distinguish between bona fide pseudotachylite friction melt and other breccia types in general, and in impact structures in particular B. How to distinguish in impact structures between bona fide pseudotachylite friction melt and injections of impact melt breccia into the crater floor...
The Lockne Crater Revision and Reassessment of Structure and Impact Stratigraphy
Maurits Lindstrom1, Jens Ormo2, Erik Sturkell3, and Ilka von Dalwigk4 department of Geology and Geochemistry, Stockholm University, S-10691 Stockholm, Sweden Maurits.Lindstrom geo.su.se 2Centro de Astrobiolog a CSIC INTA , Ctra de Torrej n y Ajalvir, km 4, E-28850 Torrej n de Ardoz, Madrid, Spain ormo inta.es 3The Icelandic Meteorological Office, Bustadarvegur 9, IS-150 Reykjavik, Iceland erik vedur.is Department of Geology and Geochemistry, Stockholm University, S-10691 Stockholm, Sweden ilka...
Iron Ore at Ternovka Ukraine
The Krivoi Rog region of Ukraine is world-famous for its gigantic iron ore deposits. A 10-11 km diameter or gt 8 km, according to Krochuk and Sharpton 2002 , perhaps originally 15-18 km large, now deeply eroded impact structure, known as Ternovka or Terny Nikolskiy 1991 Nikolskiy et al. 1981, 1982 Val'ter 1988 , is located in the Proterozoic fold belt of the Krivoi Rog basin, at 49o01'N 33o05'E. Ternovka was formed about 375 25 Ma ago. Both iron and uranium ores have been mined here from...
References Fqq
Abels A 2003 Investigation of impact structures in Finland S derfj rden, Lumparn, La aj rvi by digital integration of multidisciplinary geodata. Ph.D. thesis, Westphalian-Wilhelms University M nster, Germany, 292 pp Acu a MH 2003 Martian crustal magnetism What have we learned after 6 years of MGS observations abs. 6th International Conference on Mars abs. 3206 CD-ROM Adler JEM, Salisbury JW 1969 Circularity of lunar craters. Icarus 10 37-52 Aittola M, hman T, Kostama V-P, Raitala J 2002 Impact...
Background and General Characteristics
The conical fracturing phenomenon known as shatter cones Figs 16 and 17, 20 and 21 is widely considered shock impact diagnostic. Since the early pioneering work by Dietz 1947, 1959, 1961, 1963, 1968 , Hargraves 1961 , Manton 1962, 1965 , Milton 1977 , Milton et al. 1972, also 1996 , and Roddy and Davis 1977 , shatter cones have been described from many impact structures and have been, in many cases, the first indication for the presence of an impact structure. French 1998 defined shatter cones...
Microscopic Features Related to Shatter Cones
A comprehensive review of petrographic observations on shatter cones was presented by Nicolaysen and Reimold 1999 . Lilly 1981 concluded that shock effects due to shatter coning are only present to a depth of one or two grain diameters away from the shatter cone surface. Carter 1965 investigated planar microdeformation features in shatter cone specimens, work that resulted in one of the first detailed studies of PDFs. A related recent study is that by Hargraves and White 1996 on shatter cones...
References Lsu
Andersson M, Lax K 2000 Geokemiska kartan. Swedish Geological Survey. Report SGU- GK 2, ISSN 14004-3157 in Swedish , 49 pp Billstr m K, Weihed P 1996 Age and Provenance of host rocks and ores in the Paleopro- terozoic Skellefte District, Northern Sweden. Economic Geology 91 1054-1072 Dence MR 1971 Impact melts. Journal of Geophysical Research 76 5525-5565 Einarsson 1979 The Precambrian rocks of the Duobblon area, V sterbotten County in Swedish with English summary . Swedish Geological Survey...
Geophysical Data
In this section a short summary is given of the existing geophysical data and their characteristics. Comments on their interpretation are given in a following section. Fig. 7. VLF total intensity map of the Siljan region compiled by the Geological Survey of Sweden. The anomalies are given of the induced secondary field in o oo of the primary field. The transmitter is located to the SW in southern England . Fig. 7. VLF total intensity map of the Siljan region compiled by the Geological Survey of...
Fracture Deformations of Impact Rock Bodies
Apart from the block faulting of the Popigai crater, numerous smaller faults and fractures, which cut separate bodies of impact rocks, were discovered during large-scale mapping of selected areas within the crater these fractures are well-exposed on aerial photographs of areas composed of different impact lithologies, for example, allogenic megabreccia or suevites Fig. 5, 6 . The photogeologic guides of fractures and faults are lineaments of drainage pattern Fig. 7 zones of abundant vegetation...
General Geology of BP and Oasis Impact Structures
Both features are located in the Al Kufrah basin of southeastern Libya. At the present erosion level, the rocks that crop out at both structures are sandstones more or less ferruginous with minor conglomerates and siltstones. These rocks are strata of probably Early Cretaceous age Goudarzi 1970 Tawadros 2001 Hallett 2002 , which is generally characterized as a ferruginous, fine- to medium-grained sandstone containing abundant cross-beds, mud cracks, ripple marks and silicified wood. There has...
Introduction Oco
On Earth, meteorite impact structures are most frequently recognised in cratonic areas, mostly in Precambrian crystalline shields and surrounding platforms with sedimentary cover. The 1.9 Ga Svecofennian Crustal Domain SCD Fig. 1 , together with transitional zones to neighbouring domains, occupies part of the Fennoscandian Shield and the neighbouring NW part of the Russian Platform, where the sedimentary cover is usually lt 2 km thick Gorbatschev and Bogdanova 1993 . Data on 23 15 of known...
Paleoenvironmental Significance of Unstructured TypeIII Kerogens
The lack of major chemical differences between the S0 size fractions may be partly a result of the depositional history of the organic matter. Usually, kerogens, which appear unstructured under the petrographic microscope, are assigned as type-II kerogens and are attributed to an algal or marine origin. Type III kerogens commonly exhibit a high level of structural integrity. However, the S0 kerogen appears to have originated from a terrestrial accumulation of decomposing land plant debris,...
Hydrothermal Processes in Impact Structures
Impacts on land will involve volatiles and water of the lithosphere, and those in oceanic environments will directly affect water bodies as well as rock-bound volatiles. Even impact into arid environments will potentially result in release of volatiles through shock dissociation of hydrous minerals of the target. Interaction of aqueous solutions and other volatile components with hot, shocked rock volumes will result in hydrothermal activity, leading to effective alteration processes and...
Hydrocarbons
A 5985 m deep borehole, Gravberg 1, was sunk in 1986-1987 into the 65 to 75 km diameter Siljan impact structure in Sweden. The project endeavoured to investigate the possibility that commercial volumes of mantle-derived abiogenic methane gas could be trapped in the fractured and brecciated lower parts of the impact structure and could provide a sustainable source of energy for Sweden Casta o 1993 . This country derives much of its energy supply from hydrotechnological facilities. It was hoped...
Background Pao
The Lockne Area, Jamtland, Sweden, provides unique opportunities to study the interior structure of a relatively large impact crater. Relatively recent erosion has exposed many outcrops that can be studied geologically and geophysically. The purpose of this investigation is to investigate the correlation between electric resistivity and fracture frequency of crystalline rocks using the electro-magnetic, Very Low Frequency-Resistivity VLF- R , method. I also present the result of a modified...
Ejecta Distribution
Geological field data show that, apart from the overturned flap of crystalline ejecta, which occurs within roughly 2.5 km from the boundary of the inner crater, fragments of granite ejecta with sizes from 0.1 to 10 m lie at distances r of up to 10 to 15 km from the crater center. This seems to be the norm for land impacts, where ejecta are continuously distributed over a large area around the crater with a density roughly decreasing with distance as r McGetchin et al. 1973 . However, this is...
References Pvv
Aaloe AO 1960 Ilumetsa craters in Estonian SSR in Russian . Meteoritika 18 26-31 Abels A, Mannola P, Lehtinen M, Bergman L, Pesonen LJ 1998 New observations of the properties of the Lumparn impact structure, Aland Islands, southwestern Finland abs. . Meteoritics and Planetary Science 33 A7-A8 Abels A, Bergman L, Lehtinen M, Pesonen LJ 2000 Structural constraints and interpretations on the formation of the Soderfjarden and Lumparn impact structures, Finland abs. . In Plado J, Pesonen LJ eds...
Geological Setting
The 80-90-km-wide Vredefort Dome Gibson and Reimold 2001a,b is located in Archean and Paleoproterozoic rocks of the Kaapvaal craton of southern Africa Fig. 1 . The Dome comprises a central core of about 4550 km diameter that is composed of poly-deformed, pre-3.1 Ga, Archean granitoid gneisses and granites, with fragments of upper amphibolite to granulite facies, mafic and felsic ortho- and paragneisses. The core is surrounded by a circa 20-km-wide collar of greenschist to amphibolite facies,...
Illinois
Fig. 1. Map showing fission-track sample locations, location of the Newton County stone quarry in Kentland, Indiana, and sampled counties in Illinois LS-La Salle and Indiana C-Clark, Cl-Clay, F-Franklin, J-Jackson, L-Lake, N-Newton, and W-White . All samples collected are shown only those listed in Tables 1-5 yielded enough apatite grains gt 5 to be analyzed and used in this study. Fig. 1. Map showing fission-track sample locations, location of the Newton County stone quarry in Kentland,...
Economic Mineral Deposits in Impact Structures A Review
Wolf Uwe Reimold1, Christian Koeberl2, Roger L. Gibson1, and Burkhard O. Dressler1,3 1Impact 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 Department of Geological Sciences, University of Vienna, Althanstrasse. 14, A-1090 Vienna, Austria christian.koeberl univie.ac.at 3185 Romfield Circuit, Thornhill, Ontario, Canada, L3T 3H7 burkhard...
Oblique Impact
To investigate the influence of the impact angle we have performed 3D numerical simulations of an oblique 45o impact of a 300-m-radius granite projectile into a target consisting of crystalline basement overlain by a water layer that is 800 m deep. We used the same numerical model based on a 3D version of the SOVA hydrocode Shuvalov 1999 . The spatial resolution was lower than in the 2D simulations. The initial cell size in the central high-resolution region 100x50x80 cells was 0.025 km in both...
Epigenetic Mineralization Related to the Sudbury Structure
Ames and Gibson 1995 and Ames et al. 1997, 1998 described extensive, regional hydrothermal alteration that pervasively affected the breccia accumulations in the Sudbury basin of the Sudbury impact structure, in particular the Onaping and lower Onwatin formations. They reported evidence for a regional sub-seafloor hydrothermal system that included vertically stacked, basin-wide, semi-conformable alteration zones, in which the rocks had undergone from base to top, silicification, albitization,...
Other Deposits in and Benefits from Impact Structures
Besides metallic and mineral deposits, as discussed in detail in the above, impact structures may have much potential for other commercial or economic interests. Building materials have - for centuries - been obtained from impact structures, as, for example, witnessed by the century-old churches in Nordlingen in the Ries Crater of southern Germany and in Rochechouart in the meteorite crater of same name in the Haut-Limousin province of southwestern France. Like the medieval castle at...
References Eww
Abate B, Koeberl C, Kruger FJ, Underwood JR Jr 1999 BP and Oasis impact structures, Libya, and their relation to Libyan Desert Glass. In Dressler BO, Sharpton VL eds Large Meteorite Impacts and Planetary Evolution, Geological Society of America, Special Paper 339 177-192 Barakat AA 2001 Hypervelocity meteorite impact features within the Libyan Glass area. Annals of the Geological Survey of Egypt V XXIV. Barnes VE, Underwood JR Jr 1976 New investigations of the strewn field of Libyan Desert...
Rock Physical Properties
In-situ measurements of magnetic susceptibility and electric resistivity Fig. 7, for location see Fig. 2 were made on outcrops of gneiss and dolerite. The gneisses have low susceptibility of ca 1.8-104 SI and the dolerite has gt 100 times higher susceptibility, 3-102 SI Fig. 7a . Rock samples were measured with respect to density, magnetic susceptibility, and remanent magnetization. The gneisses and granites are generally low-magnetic, in contrast to the high-magnetic dolerite, whose magnetic...
Marquez Dome Crater
Currently some 170 impact structures are known on Earth - presumably representing a mere fraction of the entire terrestrial cratering record for a meteorite impact structure list e.g. Impact database Other solid bodies of the Solar System display surfaces that have been thoroughly cratered, but have barely been accessible for detailed impact geological study. Only the Moon and Mars have been - and will in future be - targets of direct geological study, besides probing of large, impact-cratered...
General Geology of the Popigai Crater
The 100-km-diameter Popigai impact structure Masaitis et al. 1980, 1998, 1999, and references therein formed 35.7 Ma ago Bottomley et al. 1997 at the northeast edge of the Anabar Shield, Northern Siberia. The crater was excavated within Archean crystalline rocks with overlying Proterozoic to Permian sedimentary cover with a thickness of up to 1.5 km. The crater is filled by various kinds of lithic breccias and impact melt rocks - both fragmental suevites and massive tagamites Fig. 1 . The total...
PostImpact Ore Mineralization in the VredefortWitwatersrand Structure
At Vredefort, a curiously complicated ore geological situation prevails. As explained earlier, the Archean Witwatersrand Supergroup strata of exceptional gold and uranium concentration were impacted by the Vredefort bolide some 700-900 Ma after their deposition. The current erosion level has been estimated for geological and metamorphic reasons McCarthy et al. 1986 Gibson et al. 1998 Gibson and Reimold 2000 at ca. 7-10 km. Consequently, only a deep cross-section through the central uplift is...
ConeinCone Petrography
Most cone-in-cone structures are composed of fibrous calcite and films of argillaceous material. The cone structure consists of nested and interfering cone-shaped, plumose aggregates of calcite fibers. The individual fibers are generally less than 6 m wide but may be up to 3 cm long plumose aggregates of fibers may attain 7 cm in length. The long axes of the plumose aggregates are oriented parallel to the long axes of the cones. Individual cones and cone segments are separated by argillaceous...
Newton County Stone Quarry Kentland Geology
Gutschick's 1961, 1972, 1983, 1987 detailed, high-quality maps and published descriptions show that bedding and the major faults in the Kentland quarry generally dip steeply to the north and west of the apex of the Kentland dome Fig. 3 . The major fault in the quarry, the Kentland Quarry Fault, is a folded, bedding-parallel, reverse fault between the St. Peter Sandstone and overlying Platteville Group Fig. 3 and below . The Kentland Quarry Fault and surrounding strata are folded into a steeply...
Mjolnir Impact Obliquity Constrains Models for NearField Perturbations
Numerical simulations and experimental analogues have shown that obliquity is accompanied by less energy transfer from the projectile to the target e.g., Gault and Wedekind 1978 Hayhurst et al. 1995 Schultz 1996 Burchell and Mackay 1998 Ivanov and Artemieva 2002 . The Mjolnir energy release estimates of Tsikalas et al. 1998a were made considering an elevation impact angle of 45 based, at that time, on well-known probability arguments Shoemaker 1962 Shoemaker et al. 1990 . The energy release was...
Experimental Shock Compression of Rocks
We start with a brief summary of the laboratory studies, which motivated the present numerical work. In these experiments Kenkmann et al. 2000 sized-sized two-component cylindrical rock samples were enclosed in an iron container and impacted by an iron flyer plate at 2540 m s. The experimental setup is shown schematically in Fig. 1. The individual samples consisted of two lithologies, namely quartzite and dunite, which have been chosen because they show a strong contrast in their behavior under...
References Yvj
Alexopolous JS, Grieve, RAF, Robertson PB 1988 Microscopic lamellar deformation features in quartz Discriminative characteristics of shock generated varieties. Geology 16 796-799 Baratoux D, Melosh HJ 2003 The formation of shatter cones by shock wave interference during impacting. Earth and Planetary Science Letters 216 43-54 Bjornerud MG 1998 Superimposed deformation in seconds breccias from the impact structure at Kentland, Indiana USA . Tectonophysics 290 259-269 Burtner RL, Nigrini A,...
The Sense of Pseudotachylite
Modern textbook definitions of pseudotachylite are still basically descriptive but do sometimes recognize that such breccia appears to occur in two different geological settings - tectonic fault and shear zones on the one hand, and impact structures on the other. A typical example is found in Bates and Jackson 1987 , who define pseudotachylite as a dense rock produced in the compression and shear associated with intense fault movements, involving extreme mylonitization and or partial melting....
Offsets in Brecciation and Structural Uplift
Impact craters on sedimentary targets have the advantage, in comparison with similar structures on crystalline targets, that the regular, pre-impact stratification of these targets provides reference horizons against which the impact-induced structures can be identified and mapped by seismic reflection studies. Such studies have provided an effective means of mapping the large-scale geometrical structure at depth with a high-degree of horizontal and vertical resolution e.g., Morgan and Warner...
Relation to Archean Witwatersrand Gold and Uranium Ore Deposits
The Vredefort impact structure encompasses the bulk of the Witwatersrand Basin Fig. 3 . The synclinal structure of the supracrustal sequence from the Witwatersrand to the Transvaal Supergroup in the environs of the Vredefort Dome represents effective downwarping of the stratigraphic units including those of the Witwatersrand Supergroup McCarthy et al. 1990 . This entire succession containing the gold- and uranium-rich conglomerate horizons known locally as reefs of the Witwatersrand Supergroup...
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...
BP and Oasis Impact Structures Libya Remote Sensing and Field Studies
Christian Koeberl1, Wolf Uwe Reimold2, and Jeff Plescia3 'Department of Geological Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria christian.koeberl univie.ac.at 2Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Johannesburg 2050, South Africa 3MP3-E163, Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723-6099, USA jeffrey .plescia jhuapl.edu Abstract. Remote sensing images and recent...
Shallow Excavation
To study the effect of shallow excavation we performed numerical simulations of an impact against a three-layered target. We used the same numerical model as in Ormo et al. 2002 , but increased the spatial resolution of the numerical grid 80 cells across water column and explicitly included a sedimentary layer 10 cells thick . Based on the results of previous simulations we considered the impact of a 300-m-radius stony asteroid into 800-m-deep water at a velocity of 20 km s. The crystalline...
Ynntjrnen Breccia
Since the publication of the paper of Lindstr m et al. 1983 those Middle Ordovician lower Caradoc rocks occurring in the Lockne area that contain isolated bodies of reorientated or physically disintegrated limestone, have collectively been called Lockne Breccia. The original assumption was that all of these rocks have a shared origin as debris flows. The idea of a common origin remained even after it was realized that debris flows, properly defined, had not been active. The discussion of von...
The Lockne Breccia and Loftarstone
As remarked above, the definition of the Lockne Breccia should be restricted to resurge deposits that contain clasts of crystalline ejecta. The content of limestone clasts is mostly of diverse provenance. Transitions to the overlying loftarstone may be either sharp Fig. 12 and erosional, or gradual Fig. 13 . The principal difference from the loftarstone is the smaller grain size in the latter. The sharpening of recognition criteria has led to a considerable reduction of the distribution on the...
The Mids Problematics A B S E types Tagamite and Shock Veins
Right through to the beginning of the previous decade, many workers -especially in South Africa - had remained reluctant to accept the long proposed e.g., Dietz 1960 impact origin of the Vredefort Dome. Within this context, the origin of pseudotachylite in Shand's type locality was not considered significant. It took the confirmation of bona fide shock deformation in quartz Leroux et al. 1994 and zircon Kamo et al. 1996 , and the identification of a meteoritic component in the Vredefort...
Introduction Fhs
Rock fragments or so called xenoliths are usually found within dikes inside and outside of impact craters. They are different in lithology from the country rocks of the dike walls. These fragments may be named wandering clasts, and are derived from different horizons of the target, and transported for a long distance during cratering, sometimes in opposite directions. The dimensions of clasts may vary from mm to tens of cm, they can be angular or rounded. Wandering clasts, although rare, are...
Vredefort South Africa
The most prominent progenetic ore deposits on Earth related to impact are the gold deposits of the Vredefort-Witwatersrand Basin system. The Vredefort impact structure Fig. 1 is centered on the Vredefort Dome at about latitude 27 S and longitude 27o30'E in north-central South Africa, in the heart of the Witwatersrand Basin. The origin of the Vredefort Dome was controversial for most of the 20th century see review by Gibson and Reimold 2001a . Since Du Toit 1954 published a tectonic model...
The Duobblon Structure A Small Segment of a Large Precambrian Impact Structure
Robert Lilljequist1 and Ulla Preeden2 'Ecominas, Calle Horno 9, Estepuma, Spain robertlilljequist yahoo.se 2Institute of Geology, University of Tartu, Vanemuise 46, EE-51014 Tartu, Estonia ullap ut.ee Abstract. The Duobblon Structure is located in northern Sweden, near the Scandinavian mountain range in the county of Vasterbotten. The structure constitutes a 30 km long formation, slightly concave to the NW. The Revsund Granite 1.87 Ga makes up most of the basement, and grades into a 100 m thick...
The SubCambrian Peneplain and the Crater Rim
When marine sedimentation began in large parts of Sweden in the Cambrian, it covered a surface that had been land for long enough time to cut extensive peneplain facets into the deeper, crystalline parts of Proterozoic orogens. A sub-Cambrian peneplain can thus be identified in most parts of the country where Paleozoic sedimentary rocks are preserved. In Jamtland this peneplain has got a north-westward slope of 1.5 through mainly Caledonian deformation of the lithosphere Karis and Stromberg...
Sudbury Ore Mineralization
The Cu-Ni and platinum group element ore bodies of the Sudbury Structure occur in the Sublayer, the Footwall Breccias, footwall rocks beneath the SIC, and the Offset Dikes. They are of extraordinary value. The total ore reserve is estimated at 1.65 x 109 metric tons at 1.2 Ni and 1.05 Cu. The cumulative value of ore extracted from the Sudbury Structure in more than 100 years of production has been estimated at over US 100 billion. The current production is valued at between US 1.5 and 2 billion...
Silicified ConeinCone Structures from Erfoud Morocco A Comparison with
Stefano Lugli 1, Wolf U. Reimold 2 and Christian Koeberl 3 'Dipartimento di Scienze della Terra, Universita 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...
References Ruh
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...