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2.3.4.5.6.Introduction to Terrestrial ImpactCrateringReview of Some Major ResearchStudies of Terrestrial ImpactCratersTools of AnalysisImpact Crater: Chesapeake BayWell Logging and GeochemicalStudiesImpact Cratering: EconomicPotential and Environmental EffectsConclusionJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILA1.2

January 8, 10, 15, 17, 22 10 AM to Noon5 sessions each of 2 hours25%Study/work assignments – 420%ProjectLiterature Survey &Writing a report30%Project Presentation25%Required percentage to pass this course is95%Grading: P/FJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILAThe course work involves the following:3

January 8, 2008: IAP 2008: 12.091 Session 1: P. ILAYou will gain knowledge of Criteria for identification of terrestrial impactcraters Evaluation of parameters such as size, impactorvelocity, . Research studies of age determination andcorrelation with events such as mass extinction, Economics of geological ore formation Effects of ejected deposits on the surroundingenvironment that creates an interest to pursue acareer in medical geology.4

January 10, 2008: IAP 2008 12.091 Session 2: P.ILA5

January 10, 2008: IAP 2008 12.091 Session 2: P.ILAImpact Crater Studies1. Chicxulub2. Mjolnir3. Sudbury4. Vredefort6

INTRODUCTIONWhat are the satisfactory identification criteria?What type of crater – simple or complex?What is the size?What is the age?What is composition in and around the crater?What happened to the environment?What are the significant events correlated? All these comprise the research studies of severalgroups of different/multi disciplines.January 10, 2008: IAP 2008 12.091 Session 2: P.ILAWhat are the topics of research studies?7

INTRODUCTION January 10, 2008: IAP 2008 12.091 Session 2: P.ILACurrently, more than 160 impact craters areidentified on the Earth. New impact craters aregetting identified; many research scientists are conductingstudies like further developing detailed concepts of impactcratering and impact crater structures; the global and localeffects, historical aspect of the earth, economic potential ofthe craters, numerical modeling of the impact cratering andimpact hazard and so on. Well documented web sites areproviding excellent references and images of most of theimpact craters.For this session, I selected 4 impact craters. My focus isto provide introduction and outline salient features of thesecraters.The study assignments enable familiarity of the geological,geophysical, geochemical and environmental researchstudies conducted on these craters.8

Chicxulub, Chesapeake Bay,Sudbury, Mjolnir, VredefortImpact CratersLocation, Size and AgeJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILABased l9

January 10, 2008: IAP 2008 12.091 Session 2: P.ILA10

CHICXULUB IMPACT CRATERRESEARCH 1991 – proposition of the long sought KT crater lied buried under 1000m of Cenozoic sediments at the tip fo the Yucatan peninsula Hildebrand et al.1992 -93 demonstration of the crater origin of the structure bygeophysical and lithological studies and its KT age determination byradiometric dating . - Swisher et al. 1992; Sharpton et al. 1993.1993 – multi-ring basin of impact crater – Sharpton et al.1996 - markings of cenotes on Onshore crater rim, northwestern part ofthe crater is on Offshore the Yucatan peninsula. - Pope et al.1997 - indication that the structure is a most likely a multi-ring basinwith a diameter around 200 km by offshore seismic studies Morgan etal. (1997)1997 – studies climate effects of the Chicxulub Cretaceous/Tertiaryboundary impact – Pope et al.January 10, 2008: IAP 2008 12.091 Session2: P.ILA 1981 – recognition of the gravity and magnetic anomalies centered onthe village of Chicxulub, at the tip of the Yucatan peninsula in Mexico,resemblance to those identified at large impact structures. - Penfieldand Camargo.11

CHICXULUB IMPACT CRATER RESEARCH January 10, 2008: IAP 2008 12.091 Session 2: P.ILA1998 Hydrocode simulation of the Chicxulub impactevent and the production of climatically activegases – Pierazzo et al. 1990s – Prominent satellite data and groundstudies allowed most scientists to postulate theimpact event responsible for mass extinction ofmore than 70 percent of Earth's living species 65million years ago. 2003 - NASA's righ-resolution map from ShuttleRadar Topography Mission (SRTM).SRTM has provided the most strikingly visibleevidence to date of a 180-kilometer (112-mile)wide, 900-meter (3,000-foot) deep impact crater . 12

CHICXULUB IMPACT CRATER RESEARCH 2004 -2005 - 3D Modelling of Chicxulub crater - P.M. Vermeesch and J. V. Morgan (2004)C. W. Borst and G. L. Kinsland (2005) 2004 – Impactite studies of Chicxulub StructureTuchscherer et al. 2007 - Chicxulub impact event and itsenvironmental consequences at the CretaceousTertiary boundary - D. A. Kring 2007 - Numerical modeling of impact-inducedhydrothermal activity at the Chicxulub crater- O. Abramov and D. A. Kring January 10, 2008: IAP 2008 12.091 Session 2: P.ILA13

CHICXULUB IMPACT CRATER January 10, 2008: IAP 2008 12.091 Session 2: A03377

CHICXULUB IMPACT CRATER This shaded relief image ofMexico's Yucatan Peninsulashow a subtle, butunmistakable, indication ofthe Chicxulub impact crater.Most scientists now agreethat this impact was thecause of the CretatiousTertiary Extinction, the event65 million years ago thatmarked the suddenextinction of the dinosaursas well as the majority of lifethen on Earth.Ref: fig1.jpgJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILAOriginal caption released withImage:15

CHICXULUB IMPACT CRATER Shaded relief of the YucatanPeninsula generated bydata from the Space ShuttleRadar Topography Mission. Image also illustrates theposition of the Yaxopoil-1(Yax-1) well and othersubsurface drill cores, andcrater rings based on gravitydata (Sharpton et al., 1993). 2005 seismic lines areillustrated in red, Pre-2005 are indicated bydashed black lines. Radar image courtesy ofNASA.January 10, 2008: IAP 2008 12.091 Session 2: P.ILA 16

Shuttle Radar Topography Mission (SRTM) aboardSpace Shuttle Endeavour (2000).SRTM utilized theSpaceborne Imaging Radar-C/X-Band Synthetic ApertureRadar (SIR-C/X-SAR).SRTM was designed to collect3-D measurements of the Earth's surface.200-foot mast, and additional C-band and X-bandantennas improved tracking and navigation devices.The mission is a cooperative project ofNASA, DOD, NIMANational Imagery and Mapping Agency (NIMA) ofU.S. German and Italian space agencieshttp://www.jpl.nasa.gov/srtm/January 10, 2008: IAP 2008 12.091 Session 2: P.ILACHICXULUB IMPACT CRATERSOURCE CREDITS17

CHICXULUB IMPACT CRATER January 10, 2008: IAP 2008 12.091 Session 2: P.ILA18Radar image courtesy of NASA.

CHICXULUB IMPACT CRATER January 10, 2008: IAP 2008 12.091 Session 2: P.ILAThe Yucatan plateau consists mostly limestone, is an area of very low relief elevations vary by less than few hundred metersThe computer-enhanced image is an exaggeratedtopography highlighting the semicircular trough, the darker green arcing lineat the upper left corner of the peninsula.19

CHICXULUB IMPACT CRATER January 10, 2008: IAP 2008 12.091 Session 2: P.ILAScientists believe the impact wasy centered just off the coast in the Caribbeany altered the subsurface rocksy the overlying limestone sediments formedlatery erode very easily on the vicinity of the craterrim.Formation of trough and cenotes:y the trough as well as numerous sinkholescalled cenotes are visible as small circulardepressionsy the trough is about 3 to 5 meters deep and isabout 5 km wide20

CHICXULUB IMPACT CRATER The North America and Yucatan Peninsula images created from the map are available on the JPL Planetary es/PIA03379-fig1.jpgJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILA21

PICTURE CREDITS January 10, 2008: IAP 2008 12.091 Session 2: P.ILA Picture File Name: PIA03379.jpgTarget Name: EarthIs a satellite of: Sol (our sun)Mission: Shuttle Radar Topography Mission (SRTM)Spacecraft: Space Shuttle EndeavourInstrument: C-Band Interferometric RadarProduct Size: 18001 samples x 11438 linesProduced By: JPLOrientation: North toward the top, Mercator projectionImage Data: shaded and colored SRTM elevationmodelOriginal Data Resolution: SRTM 1 arcsecond (about30 meters or 98 feet)Date Acquired: February 200022

CHICXULUB IMPACT CRATER Chicxulub impact played a major role in theCretaceous-Tertiary (KT) boundary massextinction event.Presence of strong iridium anamoliesExample of Environmental effectJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILA Thin section of the uppermost Cretaceous layer showsabundant and diversified foraminifera Very basal Paleocene, fauna has been replaced by smallopportunistic and undiversified organisms. Two faunasare separated by less than a cm of dark KT clay rich inejecta material Image of A. Montanari can be viewed athttp://we.vub.ac.be/ dglg/Web/Claeys/Web-Chix/ICDP-Chix/chixintro.html 23

CHICXULUB IMPACT CRATER Chicxulub ejecta blanket in Yucatan and Belizecomposed of dolomite blocks ranging in sizefrom a few mm to several decimeters - Pope etal. (1999) Upper Cretaceous to lower Paleogene sectionat Loma Capiro (central Cuba) provided newevidence for a Cretaceous-Paleogeneboundary age for the Chicxulub impact. Alegret et al. (2005) January 10, 2008: IAP 2008 12.091 Session 2: P.ILAChicxulub impact ejecta– evidence found in Belize and Cuba24

CHICXULUB IMPACT CRATER The ejecta plume of an impact crater consists ofmelted target rock and projectile material andsolid rock debris.It forms from extreme starting conditionswith pressures of several 100 GPawith temperatures of 10,000 C in the firstphase of the impact cratering process The ejecta plumeaccelerates in its early phase with a velocity of 5 km/sdecelerates, and finally collapses.(Melosh, 1991; Pierazzo et al.,1998), Products of this collapse are suevite rocks on the terrestrialplanets geologic recorders of this fundamental process (Kiefferand Simonds, 1980).January 10, 2008: IAP 2008 12.091 Session 2: P.ILAa highly dynamic mixture of vaporized and25

CHICXULUB IMPACT CRATER January 10, 2008: IAP 2008 12.091 Session 2: P.ILAExploration of the Chicxulub crater,YucatánPeninsula will provide information ony impact induced environmental perturbationsy the structure of large cratersy controlling groundwater flow in Yucatán statey producing proximal deposits that producehydrocarbons.The Chicxulub studyy quantify the amount of CO2, SOx and H2Oinjected in the atmosphere,y refine current climate modelsy provide better understanding of the engenderedperturbation of the global Earth System.26

Chicxulub Impact Crater - Grajales-Nishimura et al (2000)January 10, 2008: IAP 2008 12.091 Session 2: P.ILAStratigraphic and mineralogic studies ofCretaceous-Tertiary (K-T) boundary sectionsprovide the information that the offshore oilproducing breccias and seals from oil fields inthe Campeche marine platform are of K-Tboundary age and probably formed due to theK-T impact event at Chicxulub.27

CHICXULUB IMPACT CRATER January 10, 2008: IAP 2008 12.091 Session 2: P.ILASeismic and aeromagnetic data indicate that craterfloor exhalative(cfe) deposits exist on the crater floor at potentiallyeconomic depths of 1.1 km deposits may contain metallic sulfide depositsanalogous to those found on the Sudbury craterfloor a new type of exhalative sulfide deposit berecognized, the crafex category (crater-floorexhalative)- Grajales-Nishimura et al (2000)28

CHICXULUB IMPACT CRATER Estimated sulfide tonnages : Sulfides might be produced by crystallizing/coolingChicxulub melt volumes of 10,000 and 20,000 km3with estimated yield of 230 - 2,000 x 106 tonnes ofsulfides. An estimation of 50 sizeable mounds/deposits onChicxulub’s crater floor yields average sizes of 4.5 to 40x 106 tonnes.A log normal distribution model prohects that the largestdeposits equal or exceed 50 x 106 tonnes. Predictions of hydrothermal halo (e.g. Mn, Fe,Ba, Ni, Re, Pd, Co, Cr, Cu, Zn, Pb, V, S and As)associated with the crafex deposits.- Grajales-Nishimura et al (2000)January 10, 2008: IAP 2008 12.091 Session 2: P.ILAChicxulub crater’s economic potential:29

CHICXULUB IMPACT CRATERThe key question that remains is how thegigantic energy released affectedthe atmosphere,the climate,the oceans andthe organisms.January 10, 2008: IAP 2008 12.091 Session 2: P.ILA 30

January 10, 2008: IAP 2008 12.091 Session 2: P.ILA31

MJOLNIR IMPACT CRATER January 10, 2008: IAP 2008 12.091 Session 2: P.ILA32Based on image p. 291, Ref. Geology 21(1993)291-294.

Mjlonir impact crater¾ Well preserved submarine impact craterproviding wealth of information about impactcratering event and effects in marine environment¾ Search for hydrocarbon potential¾ Numerical modeling studies¾ Environmental effectsJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILAMJLONIR CRATERINTRODUCTION33

40 km in diameterAge 142 MaJurassic and Early Cretaceous periodFormed by an asteroid or comet 0.7-2.5 kmin diameterShallow sea , 5 km of sedimentary sectionone of the well preserved terrestrialsubmarine cratersJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILAMJOLNIR IMPACT STRUCTURE34

MJLONIR CRATERMARINE TARGET IMPACTMarine-target craters form only if the target sea isshallow enough to absorb sufficient kinetic energyinto the sea bed.When the crater diameter is large compared to thewater depth, the crater’s appearance resembles thecrater formed on land.January 10, 2008: IAP 2008 12.091 Session 2: P.ILAGeological features are particular to craters formed atsea. The features are most likely a result of theinfluence of the target on the cratering process.35

Melosh (1989) divides the formation of an impactcrater into three main stages: contact and compression, excavation, modification.These stages grade into one another, however, canbe crudely distinguishedJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILAMJLONIR CRATERMARINE TARGET IMPACT36

MJLONIR CRATERMARINE TARGET IMPACTJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILADifferences in the geology and morphology between the impactcraters formed on land and at sea are:Craters formed in shallow water environment: at shallow target water depths, the resulting crater featuresresemble those of a land-target impact, in shallow marine environment, a weak rim wall may developwith high water pressure, collapse of such a wall may lead to an earlyintrusion of the open sea.Craters formed in deeper water environment: are concentric, often lack melt sheets and rim walls, have deposits and radial gullies formed by the resurge of thesea impacts on the deep shelf are probably much more energeticthan is suggested by the dimensions of the preserved crater.37

MJLONIR CRATERMARINE TARGET IMPACT At greater target water depths, the resulting crateroften lacks a melt sheet and a rim wall,is concentric,has a fining-up resurge sequence,has the outer parts cut by radial gulliesthat have been eroded by resurge.The concentric shape is most probablythe result of the layered target,in combination with the higher position ofthe explosion in relation tothe preserved part of the crater in the sea floor.Formation of the inner rim wall of the crater by uplift of the basementby breccia injections.Formation of the outer rim wall in the marine-target structure in thewater mass.January 10, 2008: IAP 2008 12.091 Session 2: P.ILA 38

MJOLNIR IMPACT CRATER January 10, 2008: IAP 2008 12.091 Session 2: P.ILASearch for Hydrocarbons The hypervelocity impact contributes to the sootformation with possible initial distribution similar to thatof the accompanying ejecta. The paleogeographic position impact site at the time ofoccurrence determined to be hundreds of km from theclosest forest. Thus there would not be any ignition ofwildfires on the surrounding environment. Thus, the soot particles must have originated frompyrolysis and combustion heating of the organic rich,partly volatile, dark clays of the sea bed (HekkingenFormation). This heating should have occurred during shock wavepropagation through the target sediments together withignited sea bed before the return of the pre-impact sealevel. Soot analysis of Barents sea core samples revealedconcentrations in the range 1 ppm to 32,000 ppm.39

MJOLNIR IMPACT CRATERyyyyylogging dataseismic 2D or 3D mapping of reflecting regionalgeologic structuredownhole logging(continuous information in intermediatescale surrounding of the borehole),core data physical properties andcore data geologic age informationJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILACore- log- seismic data integration for highresolution seismic stratigraphyCore-log-seismic data integration method is aninterdisciplinary strategy, integrating coremeasurements,40

January 10, 2008: IAP 2008 12.091 Session 2: P.ILA41

SUDBURY IMPACT CRATERINTRODUCTIONJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILAThere are many studies (for more than fivedecades) on Sudbury impact structure and Sudburyigneous complex. There are more than 400references listed to date in the Sudbury impactcrater database. I will be outlining the salient features of the crater.Sudbury impact is notorious for generating the vasteconomic wealth of Ni-Fe ores and Platinum GroupElements (PGE). 42

SUDBURY IMPACT CRATERJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILA43Photo image courtesy of NASAhttp://rst.gsfc.nasa.gov/Sect18/Sect18 5.html

SUDBURY IMPACT CRATER January 10, 2008: IAP 2008 12.091 Session 2: P.ILAPhoto image courtesy of NASAhttp://rst.gsfc.nasa.gov/Sect18/Sect18 5.htmlSIR-B image legendnext slide44

SUDBURY IMPACT CRATER January 10, 2008: IAP 2008 12.091 Session2: P.ILAImage legend:Shuttle Imaging Radar Mission B (SIR-B)SIR-B radar image of the Sudbury impactstructure.The Structure is elliptical because of deformationby Grenville thrusting and the near by Wanapiteicrater filled much later.Ref:http://rst.gsfc.nasa.gov/Sect18/Sect18 5.html45

SUDBURY IMPACT CRATER January 10, 2008: IAP 2008 12.091 Session 2: P.ILAThe Sudbury Basin is the site of one of the oldestand the largest impact craters found on the Earth. Sudbury Meteorite Crater is a Multi ring Basin: Age: 1850 /- 50 Ma Diameter: 250 Km (estimated) Location: Ontario, Canada. N 46 36' W 81 11‘ Distinctive features1. Shatter cones (up to 3 m in length);2. PDF in quartz, feldspar and zircon grains;3. Overturned collar rocks of South Rangestructure4. Brecciation of country rocks occurring up to80 km from the Sudbury Igneous Complex. 46

SUDBURY IMPACT CRATER January 10, 2008: IAP 2008 12.091 Session 2: P.ILAThe Sudbury Igneous Complex occurs within theSudbury structure. The Sudbury Igneous Complex is a 2.5- to 3.0-km-thick, 60- 27-km elliptical igneous-rock body, whichconsists of four major lithologies(from top to bottom) granophyre, quartz gabbro norite,” and contact sublayer”(sulfide- and inclusion-bearing noritic rock). 47

SUDBURY IMPACT CRATER Ref:Dutch, S.I., 2001. “Significance of back-to-Back Facing Directions Along the South Range of theSudbury Igneous Complex.” Ontario, Geologic Society of America National Meeting, Boston,MA, November 7, 2001.January 10, 2008: IAP 2008 12.091 Session2: P.ILAGeologic History of the Sudbury Basin summarized by S. I. Dutch (2001) 2500-2300 MaDeposition of the Huronian Supergroup on Archean basement. Initialvolcanism was followed by deposition of a thick pelitic sequence followed bythree cycles of glacio-marine sediments interbedded with other clastic rocks 2300 MaBlezardian crustal deformation event (Riller and others, 1999). An as yetpoorly defined event manifested by folding, unconformities, and syntectonicgranitic magmatism. The basal Huronian rocks were probably tilted to nearvertical before the emplacement of the granitic plutons (Dutch, 1976). 2150 MaIntrusion of dikes and sills of Nipissing Diabase 1900-1750 MaPenokean Orogeny. Deformation and metamorphism of the Huronian rocks,also deformation, metamorphism and igneous activity in Wisconsin,Michigan, and Minnesota. 1850 MaSudbury impact event. Formation of a crater and central uplift, widespreadbrecciation of Huronian and Archean rocks, and formation of the SudburyIgneous Complex and Whitewater Group crater fill units48

The Sudbury Igneous Complex of Ontario,Canada, is the remnant of a voluminous melt sheetproduced in a few minutes by impact of a massivemeteorite into continental crust 1.85 Ga ago.The transient cavity and melting zone reached.instantly ( 2 min)relaxed to form a more familiar large,shallow crater holding a thick,superheated ( 1700 C)melt sheet covered by 2 km of breccia.Originally had a diameter of 200 to 250 km.January 10, 2008: IAP 2008 12.091 Session 2: P.ILASUDBURY IMPACT CRATER 49

Schematic illustrations of the critical stages in thedynamics of evolution leading to the final petrologicstructure of the Sudburyare provided in“The Sudbury Igneous Complex: Viscous emulsiondifferentiation of a superheated impact melt sheet”M. J. Zieg, B. D. Marsh.GSA Bulletin; November/December 2005; v. 117; no. 11/12; p. 1427–1450January 10, 2008: IAP 2008 12.091 Session 2: P.ILASUDBURY IMPACT CRATER 50

This igneous rock (called an "irruptive") is host tovast deposits of nickel and copper. This impactstructure is continuously providing a 500 billiondollar source of ore and minerals since miningbegan in the last century.Ref:From Impact to Riches: Evolution of GeologicalUnderstanding as Seen at Sudbury, CanadaA. J. NaldrettJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILASUDBURY IMPACT CRATERECONOMIC IMPORTANCEGSA Today, Volume 13, Issue 2 (February 2003) Article: pp. 4–9.51

SUDBURY IMPACT CRATER Ref:Mungall, J.E., Ames, D.E.,& Hanley, J. J.,Geochemical evidence from the Sudbury structure for crustal redistributionby large bolide impacts,Nature 429, 546-548 (3 June 2004).January 10, 2008: IAP 2008 12.091 Session 2: P.ILA Mungall, Ames and Hanley inferred (2004) that:the melt sheet preserved as the Sudbury IgneousComplex is derived predominantly from the lowercrust,the hypervelocity impact caused a partialinversion of the compositional layering of thecontinental crust.the matrix of the Onaping Formation is a mixture ofthe original surficial sedimentary strata, shockmelted lower crust and the impactor itself.52

COMPARISON OF SUDBURY ANDCHICXULUB IMPACT CRATERSJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILAPope et al (2004) compared the structure andstratigraphy of Sudbury and Chicxulub impactcraters. Chicxulub: well-preserved morphologic stateSudbury: highly-exposed ( 8 km erosion) state. Both craters have 5 structural rings with diametersof about 85, 120, 150, 200, and 250 km withsimilar character and dimensions. Chicxulub has a sixth peak ring ( 80 km)Sudbury does not have (probably due to erosion).53

COMPARISON OF SUDBURY ANDCHICXULUB IMPACT RATERS January 10, 2008: IAP 2008 12.091 Session 2: P.ILABoth Sudbury and Chicxulub are structurallysimilar 200 km diameter craters. Sudbury and Chicxulub craters are stratigraphicallydissimilar.Suevite (melt volume) of Sudbury in the centralbasin is seven times the Chicxulub. Modeling of velocity contrast between a comet andasteroid impact explained the difference in meltvolumes.Ref:Pope, K.O, Kieffer, S. W., Ames, D. E.,Empirical and theoretical comparisons of theChicxulub and Sudbury impactstructuresMeteoritics & Planetary Science ,January 2004,39(1):97-116 54

January 10, 2008: IAP 2008 12.091 Session 2: P.ILA55

VREDEFORT IMPACT CRATERJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILA56Space shuttle image STS51I-33-56AA, courtesy of NASA.

VREDEFORT IMPACT CRATERJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILAThe Vredefort crater in South Africa is the circularremnant of an impact event happened on the Earthabout 2 billion years ago. The Vredefort structure in the Archean Kaapvaalcraton of South Africa is regarded as the oldest with an estimated age of 2.02 Ga(Spray et al., 1995) the largest terrestrial impact structure, with anestimated diameter of 300 km.(McCarthy et al., 1990; Therriaultet al., 1997). 57

VREDEFORT IMPACT CRATER The Vredefort structure is located near thecenter of the Witwatersrand basin in the2.7 Ga to 3.6 Ga Kaapvaal craton.Study of Moser (1997) showed thatthe combined heating effects of the shock waveand impact-triggered magmas are considered togenerate a 300 km2 thermal imprint of the asteroidcollision with Kaapvaal craton, and account for thenearly coeval timing relationship between coremetamorphism and shock.January 10, 2008: IAP 2008 12.091 Session 2: P.ILA 58

VREDEFORT, CHICXULUB ANDSUDBURYIMPACT CRATERSJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILAGrieve and Therriault (2000) compared the available dataon the Vredefort, Sudbury, and Chicxulub craters andsummarized as follows: Vredefort, Sudbury, and Chicxulub are the largestknown terrestrial impact structures. All have multi-ring basins. All have some form of multiple-ring attributes. All have many common structural features. There are also commonalities in the structural andlithological features of Vredefort and Sudbury. It is feasible to construct a generalized compilation ofthe character of 200-300 km diameter terrestrial(Earth) impact basins Vredefort, Sudbury, and Chicxulub impactevents generated world-class mineral andhydrocarbon deposits.59

IAP 2008 12.091 ASSIGNMENT 2January 10, 2008: IAP 2008 12.091 Session 2: P.ILA1. Review the Chicxulub Impact Crater facts DiscoveryAttention to: A paleogeographic reconstructionof the continents 65 Ma. KT Boundary Mass Extinction Regional Effects Global EffectsSuggested 1.htmland the related links.Suggested reading:The Chicxulub impact event and its environmentalconsequencesat the Cretaceous–Tertiary boundaryDavid A. Kring,Palaeogeography, Palaeoclimatology, Palaeoecology 255 (2007)4–2160

IAP 2008 12.091 ASSIGNMENT 2 January 10, 2008: IAP 2008 12.091 Session 2: P.ILA2. Review the Sudbury Impact Structure Shatter cones of Sudbury impact articipants/dutch/Sudbury/SCMorphGSA99.htm Deformation studies of Sudbury impact structurehttp://gdcinfo.agg.nrcan.gc.ca/app/app4 e.html Map of the horizontal gravity gradientover the Sudbury y1 e.html Map of the horizontal gravity gradient over the SudburyStructure as it may have looked shortly after ry2 e.html61

IAP 2008 12.091 ASSIGNMENT 2 January 10, 2008: IAP 2008 12.091 Session 2: P.ILASuggested book: French, B. M., and Short, N. M.,Sudbury Structure, Ontario: Some petrographicevidence for an origin by meteorite impact, pp.383-412.;inShock metamorphism of natural materials,Proceedings of the First Conference held at NASA,Goddard Flight Center,Maryland, 1966,French, B. M., and Short, N. M., (Eds.)Mono Book Corp, Baltimore, 1968Library of Congress Catalog No. 68-59422.62

IAP 2008 12.091 ASSIGNMENT 2 4. Review the Vredefort Impact ages/vredefort.htmSuggested reading:Magnetic imaging of the Vredefort impact crater, South Africa,M. Muundjua, R. J. Hart, S. A. Gilder, L, Carporzen, A. Galdeano,Earth and Planetary Science Letters 261 (2007) 456–468.January 10, 2008: IAP 2008 12.091 Session 2: P.ILA3. Review the Mjolnir Impact Structurehttp://folk.uio.no/ftsikala/mjolnir/and browse the related linksSuggested reading:Traces of the marine Mjølnir impact eventH. Dypvik, M. Smelror, P. T. Sandbakken, O. Salvigsen, E.Kalleson,Palaeogeography, Palaeoclimatology, Palaeoecology 241 (2006)621–63663

IAP 2008 12.091 ASSIGNMENT 2 *******January 10, 2008: IAP 2008 12.091 Session 2: P.ILA5. After visiting the (web) sites of the impact crateri. What are the main features by which theterrestrial impact craters are identifiedii. What is your understanding of the importance ofthe studies of Chicxulub, Sudbury, Mjolnir andVredefort?Write briefly about each crater.64

REFERENCES FOR FURTHER READINGCHICXULUB IMPACT b1.html Chicxulub Impact Crater mages/chicxulub.htmJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILAThe Chicxulub craterhttp://we.vub.ac.be/ dglg/Web/Claeys/WebChix/ICDP-Chix/chixintro.html Terrestrial Impact Craters and Their EnvironmentalEffects 65

REFERENCES FOR FURTHER READING CHICXULUB IMPACT CRATERAbramov, O., and Kring, D. A.Numerical modeling of impact-induced hydrothermal activityat the Chicxulub crater,Meteoritics and Planetary Science, v. 42, pp. 93-112, 2007. Alegret, L., Arenillas , I., Arz, J. A., Di az, C., GrajalesNishimura, J.M., Mele ndez, A., Molina, E., Rojas,R.,Soria, A. R.Cretaceous-Paleogene boundary deposits at LomaCapiro, central Cuba: Evidence for the Chicxulub ImpactGeology; September 2005; v. 33; no. 9; p. 721–724 Alvarez, L. W., Alvarez, W., Asaro, F., and Michel, H. V.Extraterrestrial cause for the Cretaceous/Tertiary extinction,Science, 208, pp. 1095–1008, 1980. January 10, 2008: IAP 2008 12.091 Session 2: P.ILA66

REFERENCES FOR FURTHER READING CHICXULUB IMPACT CRATERJanuary 10, 2008: IAP 2008 12.091 Session 2: P.ILADressler, B. O., Grieve, R. A. F., and Sharpton, V. L.,(Eds.),Large meteorite impacts and planetary evolution,Geological Society of America Special Paper 293,pgs. 348, 1994.ISBN: 978-0813722931 French, B. M., and Short, N. M., Editors,Shock Metamorphism of Natural MaterialsMono Book Corp., Baltimore, Md., pgs. 64

CHICXULUB IMPACT CRATER RESEARCH 1981 – recognition of the gravity and magnetic anomalies centered on the village of Chicxulub, at the tip of the Yucatan peninsula in Mexico, re

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1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 We want to estimate the worst 1% of the possible outcomes. Developed for educational use at MIT and for publication through MIT OpenCourseware. No investme

djain@mit.edu, sra@mit.edu, jguo01@risd.edu, rvictor@mit.edu, raywu22@mit.edu, juschiu@mit.edu, geek@mit.edu ABSTRACT We present Amphibian, a simulator to experience scuba diving virtually in a terrestrial setting. While existing diving simulators mostly focus on visual and aural di

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3.2.1 Fokussieren mit »autofocus« 60 3.2.2 Platzhalter-Text mit »placeholder« 61 3.2.3 Verpflichtende Felder mit »required« 62 3.2.4 Noch mehr neue Attribute für das »¡nput«-Element 62 3.3 Neue Elemente 65 3.3.1 Anzeigen von Messgrdfien mit »meter« 65 3.3.2 Fortschrittsanzeige mit »progress« 68 3.3.3 Auswahllisten mit »datalist« 69

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