DOCSLIB.ORG

Shatter Cones in Hypervelocity Impact Experiments: Structure, Formation and Comparison to Natural Impact Craters

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Shatter Cones in Hypervelocity Impact Experiments: Structure, Formation and Comparison to Natural Impact Craters Shatter cones in hypervelocity impact experiments: Structure, formation and comparison to natural impact craters DISSERTATION Zur Erlangung des akademischen Grades “doctor rerum naturalium“ (Dr. rer. nat.) Der Fakultät für Umwelt und natürliche Ressourcen Der Albert-Ludwigs-Universität Freiburg i. Brsg. vorgelegt von Jakob Wilk Geb. in Berlin, Pankow Freiburg im Breisgau 2017 Dekan: Prof. Dr. Tim Freytag Erstbetreuer/Referent: Prof. Dr. Thomas Kenkmann Korreferent: Prof. Dr. Alex Deutsch Zweitbetreuer: Prof. Dr. Stefan Hergarten Tag der Disputation: ABSTRACT Impact processes have dominated the formation and development of planetary bodies in our solar system. The study of impact crater formation provides deeper knowledge of early Earth’s history and enables us to understand a surface process profoundly shaping the surface of most rocky planetary bodies. The highly dynamic process of impact cratering causes a series of characteristic effects in the targeted rocks, which are referred to as shock metamorphic effects. These shock effects provide a valuable tool to analyze impact craters and their formation. Shatter cones are diagnostic for shock metamorphism. They are the only macroscopic effect caused by shock, thus, being unambiguously identifiable in the field, provide a valuable tool to find and verify impact structures. Over the last decades, hypervelocity impact experiments and shock recovery experiments fundamentally enhanced our understanding of impact cratering, by controlled laboratory conditions. With this technique, e.g., microscopic effects were calibrated to corresponding shock pressures, or the effect of target properties on the cratering process was extensively studied. However, in only few experiments shatter cones were found and analyzed. Thus, the conditions of shatter cone formation remained unclear. Physical boundary conditions, e.g., pressure-temperature conditions or formation accompanying strain rates are unknown, as well as the timing of shatter cone formation is part of an ongoing scientific debate. By chance several shatter cone fragments where found in the MEMIN (Multidisciplinary Experimental and Modeling Impact Research Network) experiments, enabling us to systematically study the shatter cone formation. The scope of this thesis is to narrow down the physical boundary conditions of shatter cone formation, and to develop a model for their formation based on the macro- and microstructural investigations. Therefore, the MEMIN experiments were systematically analyzed to delimit the conditions under which shatter cones do or do not form. We recovered in total 24 shatter cone fragments from the ejecta of 37 MEMIN experiments. In addition, several craters showed shatter cone-like striae in the craters sub-surface. Shatter cones where recovered from nearly all target lithologies and experiments with different projectile types. We found initial impact velocity to be the driving factor when it comes to whether or not shatter cones will develop. On the basis of the microstructural analysis and iSale simulations, we determined pressure-temperature conditions to be 2- 5 GPa and in the excess of 2000°C during shatter cone formation. In addition, shear movement along the shatter cone surface has been quantified and prominent extensional features were documented. Surface parameters (e.g., apices, bifurcation, curvature, and fracture roughness) were analyzed with 3D data sets and showed good correlation of the experimentally produced shatter cones with natural samples. Also, the morphological data was used to derive a phenomenological model of shatter cone formation. As a synthesis of the experimental work we can state, that shatter cones must be formed early in the cratering process under shock compression, and that shatter cone surfaces develop as mixed-mode fracture under extremely high strain rates. 1 ZUSAMMENFASSUNG Impaktprozesse sind grundlegend die Entstehung und Entwicklung planetarer Körper in unserem Sonnensystem. Die Bildung von Meteoritenkratern zu erforschen, heißt einen Einblick in die frühe Erdgeschichte zu bekommen und einen Prozess zu verstehen, der aktiv die meisten festen planetaren Oberflächen bestimmt. Meteoriteneinschläge erzeugen eine Reihe von charakteristischen Eigenschaften im Gestein, die sogenannte Stoßwellenmetamorphose, im Zuge des hoch dynamischen Prozesses. Diese Effekte, helfen Meteoritenkrater zu erkennen und ein besseres Prozessverständnis zu entwickeln. Von diesen charakteristischen Merkmalen sind Strahlenkegel (shatter cones) der einzig makroskopische Effekt der Stoßwellenmetamorphose. Strahlenkegel sind als diagnostisches Mittel Meteoritenkrateridentifizierung anerkannt und können durch ihre sehr markanten Strukturen gut bereits im Gelände erkannt werden. Unter kontrollierten Laborbedingungen haben Hochgeschwindigkeitseinschlagsexperimente und Stoß- wellenrückgewinnungsexperimente in den letzten Jahrzenten das Verständnis von Krater- bildungsmechanismen grundlegend Verbessert. Entstehungsregime von Mikroskopischen Stoßwellen- Effekten wurden kalibriert, oder zum Bespiel der Einfluss von Porosität oder Lagenbau auf die Kraterbildung untersucht. Strahlenkegel hingegen, sind in Experimenten – auch auf Grund ihrer Häufigkeit - kaum untersucht worden. So kommt es, dass viele Aspekte der Entstehung von Strahlenkegeln immer noch unklar sind. Physikalische Rahmenbedingungen, wie Verformungsraten, Bildungsdrücke oder - temperaturen sind unklar, ebenso ist der Zeitpunkt zur Ausbildung der Strahlenkegel strittig. Die MEMIN (Multidisciplinary Experimental and Modeling Impact Research Network) Experimente gaben die Möglichkeit die Entstehung von Strahlenkegeln systematisch zu erforschen. Ziel dieser experimentellen Arbeit ist es, physikalische Rahmenparameter einzugrenzen und ein Modell zur Stahlenkegelbildung auf dieser Grundlage zu entwickeln. Hierfür sind eine Reihe Makro- und Mikrostrukturelle Analysen an den MEMIN Experimenten durchgeführt und mit natürlich gebildeten Strahlenkegeln verglichen worden. Aus dem Untersuchten Ejecta-Material von 37 MEMIN Experimenten wurden 24 Strahlenkegel-Fragmente geborgen. Darüber hinaus wurden Krateruntergründe mehrerer MEMIN Kampagnen untersucht und am Kraterboden Strahlenkegel-typische Striationen (striae) gefunden. Die Strahlenkegel wurden in fast allen Lithologien dokumentiert und es zeigte sich, dass Impakt-Geschwindigkeit der wichtigste Faktor ist um die Strahlenkegelnildung zu begünstigen. Auf Grundlage der Mikrostrukturellen Untersuchungen und iSale Modellierungen konnten die Bildungsbedingungen der gefundenen Fragmente auf 2-5 GPa und hohe Prozesstemperaturen von >2000° C abgegrenzt werden. Zudem wurden Scher- und Extensionsprozesse an den Bruchflächen dokumentiert. Oberflächeneigenschaften (Apizes, Bifurkation, Kurvatur, Rauigkeit der Bruchoberfläche) wurden mit Hilfe gewonnener 3D Daten analysiert und zeigen zum einen die Übereinstimmung der experimentellen und natürlichen Strahlenkegel, und halfen des Weiteren ein phänomenologisches Modell zu entwickeln. Aus der vorliegenden Arbeit geht hervor, dass Strahlenkegel bereit früh im Kraterbildungsprozess angelegt werden und die Bruchbildung durch Risswachstum unter Mixed-mode-Beanspruchung und extrem hohe Verformungsraten bestimmt wird. 2 STATEMENT OF THE CONTRIBUTIONS This thesis is structured as cumulative work and is comprised of the published peer-reviewed papers, and one submitted manuscripts. The PhD candidate is first author of two papers, and second author of one accepted paper. Minor contributions to publication in the form of data acquisition and single paragraphs had been made within MEMIN and in the context of crater research. This publication has been added in the appendix. The Introductory chapter has been written for this Thesis, with the intension to make an unfamiliar reader able to follow the individual publications, without any further background information being necessary. The papers are used as the chapter 2.-4. And citations are listed at the end of each chapter. The papers of this thesis are listed below: Wilk, J., and Kenkmann, T. (2016). Formation of shatter cones in MEMIN impact experiments. Meteoritics and Planetary Science 51 (8): 1477-1496. doi: 10.1111/maps.12682. Wilk., J., Hamann, C., Fazio, A., Luther, R., Hecht, L., Langenhorst, F., and Kenkmann T. (submitted). Melt formation shatter cone recovered from the MEMIN impact experiments in sandstone. Meteoritics and Planetary Science. Kenkmann T., Hergarten, S., Kuhn, T., and Wilk, J. (2016). Formation of shatter cones by symmetric fracture bifurcation: Phenomenological modeling and validation. Meteoritics and Planetary Science 51 (8): 1519-1533. doi: 10.1111/maps.12677. Note that the second paper (chapter 3) was written chronologically as the last manuscript. It was rearranged, because the developed model in chapter 4 in this thesis represents a conceptual idea grounded on observation made to a certain extend as shown in the previous chapters. The experimental work was conducted at the Fraunhofer Ernst-Mach-Institute (EMI), Freiburg, Germany by Tobias Hoerth, Christoph Michalski and Max Gulde together with EMI technicians and the MEMIN team. Herbert Ickler (Albert-Ludwigs-Universität Freiburg, ALU) prepared recovered rock samples and blocks. Surface analysis of the shatter cone samples was made with the WLI and SEM equipment available at the ALU. The MfN (Museum für Naturkunde, Berlin) offered a valuable collaboration by using their SEM for chemical mappings and their PhD Student Christopher Hamann, who made
Load more

Recommended publications
  • Cross-References ASTEROID IMPACT Definition and Introduction History of Impact Cratering Studies
    18 ASTEROID IMPACT Tedesco, E. F., Noah, P. V., Noah, M., and Price, S. D., 2002. The identification and confirmation of impact structures on supplemental IRAS minor planet survey. The Astronomical Earth were developed: (a) crater morphology, (b) geo- 123 – Journal, , 1056 1085. physical anomalies, (c) evidence for shock metamor- Tholen, D. J., and Barucci, M. A., 1989. Asteroid taxonomy. In Binzel, R. P., Gehrels, T., and Matthews, M. S. (eds.), phism, and (d) the presence of meteorites or geochemical Asteroids II. Tucson: University of Arizona Press, pp. 298–315. evidence for traces of the meteoritic projectile – of which Yeomans, D., and Baalke, R., 2009. Near Earth Object Program. only (c) and (d) can provide confirming evidence. Remote Available from World Wide Web: http://neo.jpl.nasa.gov/ sensing, including morphological observations, as well programs. as geophysical studies, cannot provide confirming evi- dence – which requires the study of actual rock samples. Cross-references Impacts influenced the geological and biological evolu- tion of our own planet; the best known example is the link Albedo between the 200-km-diameter Chicxulub impact structure Asteroid Impact Asteroid Impact Mitigation in Mexico and the Cretaceous-Tertiary boundary. Under- Asteroid Impact Prediction standing impact structures, their formation processes, Torino Scale and their consequences should be of interest not only to Earth and planetary scientists, but also to society in general. ASTEROID IMPACT History of impact cratering studies In the geological sciences, it has only recently been recog- Christian Koeberl nized how important the process of impact cratering is on Natural History Museum, Vienna, Austria a planetary scale.
    [Show full text]
  • Type Tourmalines from Brazil and Mozambique: Implications for Origin and Authenticity Determination
    No.9 May 2009 Chemical Variations in Multicolored “Paraíba”-Type Tourmalines from Brazil and Mozambique: Implications for Origin and Authenticity Determination “Cuprian-Elbaite”-Tourmaline from Mozambique “Paraiba”- Tourmaline from Brazil Manganese Mn Inner core Mn Bi Cu Bi Copper Chemical Variation in “Paraiba”-Tourmaline Chemical Distribution Mapping Editor Message from the Editors Desk: When Dr. A. Peretti, FGG, FGA, EurGeol trace element research matters most GRS Gemresearch Swisslab AG, P.O.Box 4028, 6002 Lucerne, Switzerland When copper bearing tourmalines were found 20 [email protected] years ago in the state of Paraíba in Brazil, they intrigued by their “neon”-blue color and soon became known as “Paraíba” tourmalines in the trade. In the Previous Journal and Movie years before and into the new Millennium, these tourmalines have emerged to become one of the most valuable and demanded gems, comparable to prestigious rubies and sapphires. In the last couple of years an unprecedented tourmaline boom has occurred due to the discovery of new copper-bearing tourmaline deposits. The name “Paraíba” tourmaline was originally associated only with those copper-bearing tourmalines (or “cuprian-elbaites”), which were found in the state of Paraíba (Brazil). New mines were subsequently encountered in Rio Grande do Norte in Brazil, as well as in Nigeria and in Mozambique. The market and the laboratories were split on the issue whether to call the newly discovered neon-blue colored tourmalines “cuprian-elbaites” or “Paraíba tourmaline” regardless of origin. While this controversy initiated the first high-profile law suite in the USA (currently dropped), the debate on Paraíba tourmalines progressed into a new direction.
    [Show full text]
  • STEINHEIM CRATER Steinheim Am Albuch, Steinheim Crater Is Located in the Swabain Alb
    STEINHEIM CRATER Steinheim am Albuch, Steinheim crater is located in the Swabain Alb. Since the impact a small town has been built on site. However the crater still remains popular due to it being the best preserved crater with a central uplift. Formation: The Steinheim crater is the smaller partner to the Ries crater. It is located in Alb, Steinheim. It is thought that the two craters were formed 15million years ago. However, there are two theories to how the Steinheim crater formed; either a double meteorite or a 150m fragmentation of one larger impactor as it collided with the earth to form the 24km Reis crater. In either theory, the impactor travelled at around 7.2x104 km/hour impacted the Earth. This meteorite collided with the earth with a similar amount of energy as 100,000 Hiroshima bombs. It is thought that the meteorite hit the earth’s crust at an angle between 30 and 50 degrees which, on impact, caused the pressure to increase by a million bar. As the pressure rises, the temperature also increases to 30,000 degrees causing rocks to disintegrate. Formation of a complex crater Morphology The Steinheim crater is a typical complex crater. This means it has a central uplift in the centre of the crater. The central uplift has been measured to be around 1000m in diameter and be 50m above the basin floor, and the crater itself being 3.8 km in diameter and the sides measuring to ~100m deep. However according to gravity re- searchers, the crater could in fact be double the size! Because the impact crater is exposed, it is subject to erosion and weathering and therefore the morphology of the crater has changed little each year that passes.
    [Show full text]
  • Pantasma: Evidence for a Pleistocene Circa 14 Km Diameter Impact Crater in Nicaragua
    Meteoritics & Planetary Science 1–22 (2019) doi: 10.1111/maps.13244 Pantasma: Evidence for a Pleistocene circa 14 km diameter impact crater in Nicaragua P. ROCHETTE 1*, R. ALACß 2, P. BECK3, G. BROCARD2, A. J. CAVOSIE 4, V. DEBAILLE5, B. DEVOUARD1, F. JOURDAN4, B. MOUGEL 6,11, F. MOUSTARD1, F. MOYNIER6, S. NOMADE7, G. R. OSINSKI 8, B. REYNARD9, and J. CORNEC10 1Aix-Marseille Univ., CNRS, INRA, IRD, Coll. France, CEREGE, 13545 Aix-en-Provence, France 2Basin Genesis Hub, School of Geosciences, University of Sydney, Sydney, Australia 3Univ Grenoble Alpes, CNRS, IPAG, UMR 5274, 38041 Grenoble, France 4Space Science and Technology Centre and The Institute for Geoscience Research (TIGeR), School of Earth and Planetary Science, Curtin University, Perth, Western Australia, Australia 5Laboratoire G-Time, Universite Libre de Bruxelles, Brussels, Belgium 6Institut de Physique du Globe de Paris, Universite Sorbonne Paris Cite, CNRS UMR 7154, Paris, France 7LSCE, CEA, CNRS UVSQ et Universite´de Paris Saclay, 91190 Gif sur Yvette, France 8Centre for Planetary Science and Exploration and Department of Earth Science, University of Western Ontario, London, Canada 9University of Lyon, ENS de Lyon, Universite´Claude Bernard Lyon 1, CNRS, UMR 5276 LGL-TPE*, 69007 Lyon, France 10Geologist, Denver, USA 11Present address: Centro de geociencias, Universidad Nacional Autonoma de Mexico, Campus Juriquilla, Queretaro *Corresponding author. E-mail: [email protected] (Received 07 March 2017; revision accepted 15 December 2018) Abstract–The circa 14 km diameter Pantasma circular structure in Oligocene volcanic rocks in Nicaragua is here studied for the first time to understand its origin. Geomorphology, field mapping, and petrographic and geochemical investigations all are consistent with an impact origin for the Pantasma structure.
    [Show full text]
  • Annual Report COOPERATIVE INSTITUTE for RESEARCH in ENVIRONMENTAL SCIENCES
    2015 Annual Report COOPERATIVE INSTITUTE FOR RESEARCH IN ENVIRONMENTAL SCIENCES COOPERATIVE INSTITUTE FOR RESEARCH IN ENVIRONMENTAL SCIENCES 2015 annual report University of Colorado Boulder UCB 216 Boulder, CO 80309-0216 COOPERATIVE INSTITUTE FOR RESEARCH IN ENVIRONMENTAL SCIENCES University of Colorado Boulder 216 UCB Boulder, CO 80309-0216 303-492-1143 [email protected] http://cires.colorado.edu CIRES Director Waleed Abdalati Annual Report Staff Katy Human, Director of Communications, Editor Susan Lynds and Karin Vergoth, Editing Robin L. Strelow, Designer Agreement No. NA12OAR4320137 Cover photo: Mt. Cook in the Southern Alps, West Coast of New Zealand’s South Island Birgit Hassler, CIRES/NOAA table of contents Executive summary & research highlights 2 project reports 82 From the Director 2 Air Quality in a Changing Climate 83 CIRES: Science in Service to Society 3 Climate Forcing, Feedbacks, and Analysis 86 This is CIRES 6 Earth System Dynamics, Variability, and Change 94 Organization 7 Management and Exploitation of Geophysical Data 105 Council of Fellows 8 Regional Sciences and Applications 115 Governance 9 Scientific Outreach and Education 117 Finance 10 Space Weather Understanding and Prediction 120 Active NOAA Awards 11 Stratospheric Processes and Trends 124 Systems and Prediction Models Development 129 People & Programs 14 CIRES Starts with People 14 Appendices 136 Fellows 15 Table of Contents 136 CIRES Centers 50 Publications by the Numbers 136 Center for Limnology 50 Publications 137 Center for Science and Technology
    [Show full text]
  • Glossary Glossary
    Glossary Glossary Albedo A measure of an object’s reflectivity. A pure white reflecting surface has an albedo of 1.0 (100%). A pitch-black, nonreflecting surface has an albedo of 0.0. The Moon is a fairly dark object with a combined albedo of 0.07 (reflecting 7% of the sunlight that falls upon it). The albedo range of the lunar maria is between 0.05 and 0.08. The brighter highlands have an albedo range from 0.09 to 0.15. Anorthosite Rocks rich in the mineral feldspar, making up much of the Moon’s bright highland regions. Aperture The diameter of a telescope’s objective lens or primary mirror. Apogee The point in the Moon’s orbit where it is furthest from the Earth. At apogee, the Moon can reach a maximum distance of 406,700 km from the Earth. Apollo The manned lunar program of the United States. Between July 1969 and December 1972, six Apollo missions landed on the Moon, allowing a total of 12 astronauts to explore its surface. Asteroid A minor planet. A large solid body of rock in orbit around the Sun. Banded crater A crater that displays dusky linear tracts on its inner walls and/or floor. 250 Basalt A dark, fine-grained volcanic rock, low in silicon, with a low viscosity. Basaltic material fills many of the Moon’s major basins, especially on the near side. Glossary Basin A very large circular impact structure (usually comprising multiple concentric rings) that usually displays some degree of flooding with lava. The largest and most conspicuous lava- flooded basins on the Moon are found on the near side, and most are filled to their outer edges with mare basalts.
    [Show full text]
  • The Origin of the Circular K Anomalies at the Bosumtwi Impact Structure
    Large Meteorite Impacts VI 2019 (LPI Contrib. No. 2136) 5008.pdf THE ORIGIN OF THE CIRCULAR K ANOMALIES AT THE BOSUMTWI IMPACT STRUCTURE. C.A.B. Niang1,2,3, D. Baratoux3, D.P. Diallo1, R. Braucher4, P. Rochette4, C. Koeberl5, M.W. Jessell6, W.U. Reimold7, D. Boamah8, G. Faye9, M.S. Sapah10, O. Vanderhaeghe3, S. Bouley11. 1Département de Géologie, Université Cheikh Anta Diop, Dakar, Senegal, [email protected], 2Institut Fon- damental d’Afrique Noire Cheikh Anta Diop, Dakar, Senegal. 3Géosciences Environnement Toulouse, University of Toulouse, CNRS & IRD, 14, Avenue Edouard Belin, 31400, Toulouse, France. 4Centre Européen de Recherche et d’Enseignement des Géosciences et de l’Environnement, Aix-Marseille Université, CNRS, IRD, CEREGE UM34, Aix en Provence, France, 5Department of Lithospheric Research, University of Vienna, 1090 Vienna, Austria, and Natural History Museum 1010 Vienna, Austria. 6Centre for Exploration Targeting, The University of Western Aus- tralia, 35 Stirling Highway, Crawley, WA 6009, Australia. 7Institute of Geosciences, Laboratory of Geodynamics, Geochronology and Environmental Science, University of Brasília, Brasília, Brazil. 8Geological Survey Department, Accra, Ghana. 9Institut des Sciences de la Terre, Université Cheikh Anta Diop de Dakar, Sénégal.10Department of Earth Science, University of Ghana, Accra, Ghana. 11GEOPS - Géosciences Paris Sud, Univ. Paris-Sud, CNRS, Université Paris-Saclay, Rue du Belvédère, Bât. 504-509, 91405 Orsay, France Introduction: Radiometric data are commonly to weathering, erosional and transport processes. Sev- used for geological mapping in mineral exploration, eral samples were also taken at surface and combined particularly in tropical regions where outcrop condi- with samples from shallow boreholes used for cosmo- tions are poor.
    [Show full text]
  • Imagining Outer Space Also by Alexander C
    Imagining Outer Space Also by Alexander C. T. Geppert FLEETING CITIES Imperial Expositions in Fin-de-Siècle Europe Co-Edited EUROPEAN EGO-HISTORIES Historiography and the Self, 1970–2000 ORTE DES OKKULTEN ESPOSIZIONI IN EUROPA TRA OTTO E NOVECENTO Spazi, organizzazione, rappresentazioni ORTSGESPRÄCHE Raum und Kommunikation im 19. und 20. Jahrhundert NEW DANGEROUS LIAISONS Discourses on Europe and Love in the Twentieth Century WUNDER Poetik und Politik des Staunens im 20. Jahrhundert Imagining Outer Space European Astroculture in the Twentieth Century Edited by Alexander C. T. Geppert Emmy Noether Research Group Director Freie Universität Berlin Editorial matter, selection and introduction © Alexander C. T. Geppert 2012 Chapter 6 (by Michael J. Neufeld) © the Smithsonian Institution 2012 All remaining chapters © their respective authors 2012 All rights reserved. No reproduction, copy or transmission of this publication may be made without written permission. No portion of this publication may be reproduced, copied or transmitted save with written permission or in accordance with the provisions of the Copyright, Designs and Patents Act 1988, or under the terms of any licence permitting limited copying issued by the Copyright Licensing Agency, Saffron House, 6–10 Kirby Street, London EC1N 8TS. Any person who does any unauthorized act in relation to this publication may be liable to criminal prosecution and civil claims for damages. The authors have asserted their rights to be identified as the authors of this work in accordance with the Copyright, Designs and Patents Act 1988. First published 2012 by PALGRAVE MACMILLAN Palgrave Macmillan in the UK is an imprint of Macmillan Publishers Limited, registered in England, company number 785998, of Houndmills, Basingstoke, Hampshire RG21 6XS.
    [Show full text]
  • Evidence for Impact-Generated Deposition
    EVIDENCE FOR IMPACT-GENERATED DEPOSITION ON THE LATE EOCENE SHORES OF GEORGIA by ROBERT SCOTT HARRIS (Under the direction of Michael F. Roden) ABSTRACT Modeling demonstrates that the Late Eocene Chesapeake Bay impact would have been capable of depositing ejecta in east-central Georgia with thicknesses exceeding thirty centimeters. A coarse sand layer at the base of the Upper Eocene Dry Branch Formation was examined for shocked minerals. Universal stage measurements demonstrate that planar fabrics in some fine to medium sand-size quartz grains are parallel to planes commonly exploited by planar deformation features (PDF’s) in shocked quartz. Possible PDF’s are observed parallel to {10-13}, {10-11}, {10-12}, {11-22} and {51-61}. Petrographic identification of shocked quartz is supported by line broadening in X-ray diffraction experiments. Other impact ejecta recognized include possible ballen quartz, maskelynite, and reidite-bearing zircon grains. The layer is correlative with an unusual diamictite that contains goethite spherules similar to altered microkrystites. It may represent an impact-generated debris flow. These discoveries suggest that the Chesapeake Bay impact horizon is preserved in Georgia. The horizon also should be the source stratum for Georgia tektites. INDEX WORDS: Chesapeake Bay impact, Upper Eocene, Shocked quartz, Impact shock, Shocked zircon, Impact, Impact ejecta, North American tektites, Tektites, Georgiaites, Georgia Tektites, Planar deformation features, PDF’s, Georgia, Geology, Coastal Plain, Stratigraphy, Impact stratigraphy, Impact spherules, Goethite spherules, Diamictite, Twiggs Clay, Dry Branch Formation, Clinchfield Sand, Irwinton Sand, Reidite, Microkrystite, Cpx Spherules, Impact debris flow EVIDENCE FOR IMPACT-GENERATED DEPOSITION ON THE LATE EOCENE SHORES OF GEORGIA by ROBERT SCOTT HARRIS B.
    [Show full text]
  • AND GEOLOGY of the SURROUNDING AREA I
    . " ... , - .: ~... GP3/10 ~ " . :6',;, J .~~- -i-~ .. '~ MANITOBA MINES BRANCH DEPARTMENT OF MfNES AND NATURAL RESOURCES LAKE ST. MARTIN CRYPTO~EXPLOSION CRATER .. AND GEOLOGY OF THE SURROUNDING AREA i . , - by H. R. McCabe and B. B. Bannatyne Geological Paper 3/70 Winnipeg 1970 Electronic Capture, 2011 The PDF file from which this document was printed was generated by scanning an original copy of the publication. Because the capture method used was 'Searchable Image (Exact)', it was not possible to proofread the resulting file to remove errors resulting from the capture process. Users should therefore verify critical information in an original copy of the publication. (i) GP3/10 MANITOBA M]NES BRANCH DEPARTMENT OF MINES AND NATURAL RESOURCES LAKE ST. MARTIN CRYPTO·EXPLOSION CRATER AND GEOLOGY OF THE SURROUNDING AREA by H. R. McCabe and B. B. Bannatync • Geological Paper 3/70 Winnipeg 1970 (ii) TABLE OF CONTENTS Page Introduction' r Previous work I .. Present work 2 Purpose 4 Acknowledgcmcnts 4 Part A - Regional geology and structural setting 4 Post-Silurian paleogeography 10 Post-crater structure 11 Uthology 11 Precambrian rocks 12 Winnipeg Fomlation 13 Red River Fomlation 14 Stony Mountain Formation 15 Gunn Member 15 Gunton Member 16 Stoncwall Formation 16 Interlake Group 16 Summary 17 Part B - Lake St. Martin crypto-explosion crater 33 St. Martin series 33 Shock metamorphism 33 Quartz 33 Feldspar 35 Biotite 35 Amphibole 36 Pseudotachylyte 36 Altered gneiss 37 Carbonate breccias 41 Polymict breccias 43 Aphanitic igneous rocks - trachyandcsitc 47 Post·crater Red Beds and Evaporites (Amaranth Formation?) 50 Red Bed Member 50 Evaporite Member 52 Age of Red Bed·Evaporite sequence 53 Selected References 67 .
    [Show full text]
  • Shatter Cone and Its Surface Mesh-Structure Formed by Impact
    SHATTER CONE AND ITS SURFACE MESHED- STRUCTURE FORMED BY IMPACT MELT-GASIFICATION IN XISHAN TAIHU LAKE CHINA H.N. Wang1, Y. Chen1, X.F. Shen1 L.Y. Zhou1 and Y.W. Wang2 11Department of Earth & Planetary Sciences, Nanjing University, Nanjing, China 210093 ([email protected]) 2 Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign, Champaign Introduction: Meshed--structure shatter cone: Discuss ion: Shatter cones are represented by a range of curved to The height of these cones is generally 50 to 70 cm. The 1. Meshed-structure are related to the melt- curvilinear fractures decorated with divergent striations. striation radiates from the original point at the top of cone, gasification of carbonates target rock: Striations radiate from an apex of a conical feature or from a similar to the longitude meridian. Meanwhile, cone surface Carbonates are brittle, fusible and volatile. Under the narrow apical area. Shatter cones are the only distinct meso shock wave, it is easy to be granulated. Its melting point presents hoopline around the cone. (Fig.D) The grid on is as low as 500-600°C. When the shock wave pass to macroscopic recognition criterion for impact structures. cone surface is generally in centimeter scale (2-4cm x Despite being known for 110 yrs, the formation mechanism through, it melts instantly and forms the atherosclerotic 2-3cm), latitude and longitude lines form a grid meshed- fluid, leaving a meshed structure and imprints after of shatter cone remains unclear. Different hypotheses for structure. This is an important and unique phenomenon cooling.
    [Show full text]
  • Impact Cratering in the Solar System
    Impact Cratering in the Solar System Michelle Kirchoff Lunar and Planetary Institute University of Houston - Clear Lake Physics Seminar March 24, 2008 Outline What is an impact crater? Why should we care about impact craters? Inner Solar System Outer Solar System Conclusions Open Questions What is an impact crater? Basically a hole in the ground… Barringer Meteor Crater (Earth) Bessel Crater (Moon) Diameter = 1.2 km Diameter = 16 km Depth = 200 m Depth = 2 km www.lpi.usra.edu What creates an “impact” crater? •Galileo sees circular features on Moon & realizes they are depressions (1610) •In 1600-1800’s many think they are volcanic features: look similar to extinct volcanoes on Earth; some even claim to see volcanic eruptions; space is empty (meteorites not verified until 1819 by Chladni) •G.K. Gilbert (1893) first serious support for lunar craters from impacts (geology and experiments) •On Earth Barringer (Meteor) crater recognized as created by impact by Barringer (1906) •Opik (1916) - impacts are high velocity, thus create circular craters at most impact angles Melosh, 1989 …High-Velocity Impacts! www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/Animation.gif Physics of Impact Cratering Understand how stress (or shock) waves propagate through material in 3 stages: 1. Contact and Compression 2. Excavation 3. Modification www.psi.edu/explorecraters/background.htm Hugoniot Equations Derived by P.H. Hugoniot (1887) to describe shock fronts using conservation of mass, momentum and energy across the discontinuity. equation (U-up) = oU of state P-Po = oupU E-Eo = (P+Po)(Vo-V)/2 P - pressure U - shock velocity up - particle velocity E - specific internal energy V = 1/specific volume) Understanding Crater Formation laboratory large simulations explosives (1950’s) (1940’s) www.nasa.gov/centers/ames/ numerical simulations (1960’s) www.lanl.gov/ Crater Morphology • Simple • Complex • Central peak/pit • Peak ring www3.imperial.ac.
    [Show full text]