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Meteorite Impacts, Earth, and the Solar System Traces of Catastrophe A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures Bevan M. French Research Collaborator Department of Mineral Sciences, MRC-119 Smithsonian Institution Washington DC 20560 LPI Contribution No. 954 i Copyright © 1998 by LUNAR AND PLANETARY INSTITUTE The Institute is operated by the Universities Space Research Association under Contract No. NASW-4574 with the National Aeronautics and Space Administration. Material in this volume may be copied without restraint for library, abstract service, education, or personal research purposes; however, republication of any portion thereof requires the written permission of the Insti- tute as well as the appropriate acknowledgment of this publication. Figures 3.1, 3.2, and 3.5 used by permission of the publisher, Oxford University Press, Inc. Figures 3.13, 4.16, 4.28, 4.32, and 4.33 used by permission of the publisher, Springer-Verlag. Figure 4.25 used by permission of the publisher, Yale University. Figure 5.1 used by permission of the publisher, Geological Society of America. See individual captions for reference citations. This volume may be cited as French B. M. (1998) Traces of Catastrophe:A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures. LPI Contribution No. 954, Lunar and Planetary Institute, Houston. 120 pp. This volume is distributed by ORDER DEPARTMENT Lunar and Planetary Institute 3600 Bay Area Boulevard Houston TX 77058-1113, USA Phone:281-486-2172 Fax:281-486-2186 E-mail:[email protected] Mail order requestors will be invoiced for the cost of shipping and handling. Cover Art.“One Minute After the End of the Cretaceous.” This artist’s view shows the ancestral Gulf of Mexico near the present Yucatán peninsula as it was 65 m.y. ago, just after the impact of an asteroid or comet about 10 km in diameter began to form the huge Chixculub (Mexico) impact structure. In only a minute after the impact, a transient crater about 100 km across has been excavated, cutting through the surface ocean water, the underlying carbonate sediments, and the deep-seated crystalline crustal rocks. The edge of the growing transient crater is marked by a curtain of material that is being ejected into the atmosphere. Earth’s Moon appears as a small dot above and to the left of the ejecta curtain. Painting by William K. Hartmann; used by permission of the artist. ii Dedicated to Ralph B. Baldwin Robert S. Dietz Eugene M. Shoemaker Who were so far ahead Of all the rest of us. iii iv Contents Chapter 1: LANDSCAPES WITH CRATERS: METEORITE IMPACTS, EARTH, AND THE SOLAR SYSTEM ........................................................................................... 1 1.1. The New Geology: Meteorite Impacts on the Earth ................................................................................................ 1 1.2. The Planetary Perspective......................................................................................................................................... 4 1.3. A Peculiar Process: Why Impacts are Different ........................................................................................................ 6 1.3.1. Rarity ....................................................................................................................................................... 7 1.3.2. Immense Energy ...................................................................................................................................... 7 1.3.3. Instant Effects .......................................................................................................................................... 7 1.3.4. Concentrated Energy Release................................................................................................................... 8 1.3.5. Extreme Physical Conditions ................................................................................................................... 9 1.3.6. Unique Deformation Effects .................................................................................................................. 10 Chapter 2: TARGET EARTH: PRESENT, PAST, AND FUTURE .................................................................11 2.1. Comets and Asteroids: The Killer Neighbors? ....................................................................................................... 11 2.1.1. Asteroids ................................................................................................................................................ 11 2.1.2. Comets ................................................................................................................................................... 11 2.1.3. Close Encounters .................................................................................................................................... 12 2.2. In Our Time: Small Catastrophes.......................................................................................................................... 12 2.3. The Problems of Prediction: How Big, How Often? .............................................................................................. 12 2.3.1. Ingredients of Catastrophe ...................................................................................................................... 12 2.3.2. Uncertain Estimates ................................................................................................................................ 13 2.3.3. An Uncertain Future? ............................................................................................................................. 16 Chapter 3: FORMATION OF IMPACT CRATERS ........................................................................................17 3.1. Shock Waves and Crater Formation ....................................................................................................................... 17 3.1.1. Contact/Compression Stage ................................................................................................................... 18 3.1.2. Excavation Stage: The Transient Crater ................................................................................................. 20 3.1.3. Modification Stage ................................................................................................................................. 23 3.2. Simple and Complex Impact Structures .................................................................................................................. 23 3.2.1. Simple Craters ........................................................................................................................................ 23 3.2.2. Complex Craters ..................................................................................................................................... 24 3.2.3. Multiring Basins ..................................................................................................................................... 27 3.3. Subsequent Development of Impact Structures ...................................................................................................... 28 Chapter 4: SHOCK-METAMORPHIC EFFECTS IN ROCKS AND MINERALS .......................................31 4.1. Formation Conditions and General Characteristics ................................................................................................. 31 4.2. Stages of Shock Metamorphism ............................................................................................................................. 36 4.3. Megascopic Shock-Deformation Features: Shatter Cones ...................................................................................... 36 4.4 High-Pressure Mineral Polymorphs ........................................................................................................................ 40 4.5. Planar Microstructures in Quartz ........................................................................................................................... 42 4.5.1. Planar Fractures ...................................................................................................................................... 42 4.5.2. Planar Deformation Features (PDFs) ...................................................................................................... 42 4.5.3. PDF Orientations ................................................................................................................................... 49 4.5.4. PDFs in Sedimentary Rocks ................................................................................................................... 52 4.6. Planar Microstructures in Feldspar and Other Minerals .......................................................................................... 53 4.7. Shock Isotropization and Diaplectic Glasses ........................................................................................................... 55 4.8. Selective Mineral Melting ...................................................................................................................................... 57 v Chapter 5: SHOCK-METAMORPHOSED ROCKS (IMPACTITES) IN IMPACT STRUCTURES .................................................................................................................61 5.1. Rock Types in the Final Impact Structure ............................................................................................................... 61 5.2. Classification
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