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A Previously Undescribed Meteorite Crater in Chile

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A Previously Undescribed Meteorite Crater in Chile JOURNALOF GEOPHYSICALRrSrARC•r VOL. 71, No. 20 OCTO•.R 15, 1966 A Previously UndescribedMeteorite Crater in Chile• JOAQUIN SANCItEZ Instituto de Investigaciones Geologicas Santiago, Chile WILLIAM CASSIDY Lamont Geological Observatory, Columbia University Palisades, New York A previously undescribedmeteorite crater having dimensions of 455 m average diameter and 31 m average depth has been discovered in northern Chile at 23ø55.6'S, 68ø16.7'W. Me- teorites have not been recovered, but iron shale and impactite material verify its meteoritic origin. The crater is eraplacedin granite, overlain by a thin ignimbrite sheet. From the ap- parent disruption of the local Pleistocene drainage pattern, the age of formation of the crater must be Pleistoceneor Recent. It may have been formed by the same meteoroid that created the Campo del Cielo cratersin Argentina. The name Monturaqui crater is proposed. INTRODUCTION pressionsstill contain a 4- to 5-m thicknessof A cooperativeprogram has been established ignimbrite but where previous granite promi- between the Chilean Instituto de Investiga- nences are once again exposed. Both granite ci6nes Geo16gicasand Lamont Geological Ob- and ignimbrite crop out in the walls and rim servatory of Columbia University for field crest of the crater, but the rim crest is almost studies on meteorites and meteorite craters. completelymantied with ignimbrite. Small-scale stratification is not obvious in During November 1965, we visited a crater- like feature that had been located on aerial the ignimbrite layer, but a prominent fracture photographs by Sanchez 3 years earlier. At or jointing plane, visible at scattered points that time he had noted that the crater did in the rim, slopesradially outward (Figure 2), not appear to be volcanic, and he conjectured suggestinguplift. From the aerial photograph that it might be a meteorite crater. During (Figure 3) it seemsprobable that the sudden our visit we collected meteortrio iron shale formation of the crater cut off pre-existing and impact (?) glass on the rim crest and drainage gullies and forced the upstream seg- flanks of the crater, thus verifying Sanchez's ments into a new pattern around the flanks of speculations. the crater; therefore, we assign the formation of the crater to a time after a drainage system LOCATION AND DESCRIPTION had developedin the Upper Tertiary-to-Pleis- The crater is located in the precordilleran tocene ignimbrites. ranges south of the Salar de Atacama at The diameter of the crater is 470 m E-W X 23ø55.6'S,68ø16.7'W (Figure 1). It is emplaced 440 m N-S. The wall height is very variable, in Jurassicgranite that locally is cut by centi- ranging from 16 to 48 m above the low point. meters-wide dikes of phaneritic texture and The variable wall height was probably caused probably basic composition.The ancient ero- by topographicirregularities in the pre-impact sion surface of the granite is overlain uncon- surface. The low point, seen in the aerial formably by Upper Tertiary or Pleistocene photograph as a white spot of fine clay and ignimbrite.The crater lies near the edgeof this silt, is off-center toward the northeast; thus sheet,in a zone where earlier topographicde- the crater is somewhatasymmetric. METEORITIC MATERIALS AND IMPACT PRODUCTS • Lamont Geological Observatory Contribution 944. Material like that shown in Figure 4 was 4891 4892 SANCHEZ AND CASSIDY 71' 70' 69 ø 22' CHUQUlCAMATA PACIFIC OCEAN SAN PE DE ATACAMA • 25ø ANTOFAGASTA I 24-- CF'ATEF'........•o ----• 24- MONTURAQUI ,50 I00 Km so/co..^ss Fig. 1. Map of part of Chile showinglocation of. the crater, just south of the Salar de Atacama. The Salar is one of a number of evaporite plans found commonly in the Atacama Desert and the/-/igh Cordillera of northern Chile. :::??:........;::.".""--'"..:i'•Z:•:'"":'?:"""*" "'•'""'" •; .......... <':':::*""'•:'•:•....--'•?-:•2• ":'"-'":•:% :.-.• .................. • '::':..".... :."" .-,.:. ,•:_•::%•. *' .:..:%• :•'::•-*....::,,...•.... ":•':"....... ,...: - '"'":::.•....:..vs.--,:'.:,. -.'::"•i!"..-'..•:::•:'•*'.-"•'...... ::•.4•:i::. ...... '--:..... :':.-'.-.":-•' -?..•:.'*•:: .... ...'.....•' ........ o•4,:--•.::•::'•.•/-!.-•:•c*.-'"' .•: ' '--•::!6•%-;::-•-"•.-':•::.-'.:-;•!:•:::'.-'-'.i:;•-::, ...........*•,.'•..-'--.-•iii•:::::•:'•. '•-- .............. i'•-.•;•".-2.-'.:.•.,:::'-. ...."'•:•!:::•;':•.?.-•::•>•': .-.•.•: ......... ............. "•::;:'::..-::..-.-':•.• -":;::•-'.-:•'-:• ........... •:".:.ß .. 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'::;!'..*..!;?<:• .;,...: •!:..:...?....... -.'..'.'.!-•-;-'?:!:•'.'?:•.•.•-:. •":':..-.:!•.•:::-;r•!•.?..'::."i'.-'..'•:• ......•'•:"-.•::•?.•::" .-.•."...... *,.. **:.'r:'-".'-;•.'::!.:;•;"•.•.'• ..:":z:•:-'::•-".!•:.-'•;•,2•.... .:.:::::::.,:..:::•<.. ß:!.-'.-'•i,<::•:;i•i;; .-'...-'.:•.*:r.-'•..-'.<.':•:-:• "'.'.•.• ..*.:: '"'%...... ' :;:.::•i? ..'i.•!;'.:?..---*.-'i•:.:.:•!•;i*.::•:•ii :'?""•"' .'•,. ..::-•..-::-:, ' •".;/:•i;;"."-•iiii.;'.•. •,,.•:.,.:,•, .•:,•'.':•,.:.-•::• .;..:.•;..-';':•.....;:ß..... :: :::-:::":•:•?•:.................... .... .'.•.•'"-,*'-'*•.'.'• ./•. • ' .:•ii•'.:.'...i'..::-' Fig. 2. Photograph of ignimbri[e blocks at the rim crest of the cra[er. They appear to be tilted up towardthe risht. Centerof the crateris to the right. METEORITE CRATER IN CHILE 4893 Pig. 3. Aerial pho•ographof the crater.North is at the •op. The •eatureis approximately 450 m in diameter.The white spot inside the crater is fine clay and silt accumulated•t the low point. Note the two drainagegullies approaching the crater œromthe south; •hey have apparently been diverted by the rim flanks of the crater. Short gullies now draining •he northeast rim flank were probably their downstream continuations beœoreœormation oœ the crater. found at points on tl•e north and southwest of the crater; all specimensoriginally lying- rim and south flank of the crater, and it is on the surface could have been picked up by undoubtedly a meteoritic iron shale. The iron passingherdsmen and traders. This llama trail shale is magnetic. The specimensshown in is a historicallyimportant route runningœrom Figure 5, found in great abundance on the the Pacific coast through Monturaqui to San south and southeastflanks of the crater, are Pedro de Atacama and finally acrossthe cordil- probably impactires.These consistof porous lera into northern Argentina [Fletcher, 1889]. cindery aggregates containing fragments of It is conceivable,therefore, that many of the granite and are bonded with glass. Many of iron meteorites reported
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