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.

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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 from other localities them are weakly magnetic,which suggeststhat they contain metallic iron. Specimensas large in Chile were originally found at this crater. as first size were found. No meteorites were For this reason it will be of great interest to found on the surface,but this is not surprising recover a meteorite specimenfrom the crater because a llama trail crosses the outer flank site. 4894 SANCHEZ AND CASSIDY

Fig. 4. Meteoriticiron shalefound on the rim and flanksof the crater.The largestspecimen is 5 cm across.

Fig. 5. Impact(?) glassfound on the rim and flanksof the crater.The cinderyaggregates differ in colorand texturefrom pumiceousand slaggyvolcanic bombs of the region.They are found associatedwith the crater only. The largestspecimen is ? cm across. METEORITE CRATER IN CHILE 4895 I)ISCUSSION speculationsthere is no reason to believe the two are related. They could be related, how- Large features that appear to be impact ever, if the meteoroid that caused the Campo craters in the granitie shield areas of Canada del Cielo crater field had a 25-hour period, and have been described [Innes, 1964; Dence, this possibility is being investigated.Support- 1965]. Because this crater was emplaced in ing evidence would be additional craters ar- granite, its geological relations and impact ranged along azimuth 60ø, close similarity of productsare expectedto be more than normally meteoritie material from the two sites, and interesting.It is possible,too, that details of its equal agesof formation of the two occurrences. structure may be more directly comparable with those of the Canadian craters, and of NOMENCLATURE lunar craters, than with those of other ter- The town nearest to the crater is the village restrial meteorite craters that have been formed of Peine, some 35 km to the northeast. The in sediments. next closesttown is Monturaqui, approximately The present cooperativeresearch program 70 km to the south. Because Monturaqui is between Lamont GeologicalObservatory and better known and the crater is located in the the Instituto de Investigaci6nesGeo16gicas was northern extension of the Monturaqui moun- set up as the result of findingsby Cassidyet al. tain range, we proposethat the crater be called [1965], who suggestedthe possibility of the the Monturaqui crater. existence in northern Chile of one or more meteorite craters formed by the fall of me- Acknowledgments. The field investigations re- teorites that had survived a previous orbital ported here were supported in part by the In- stituto de Investigaci6nesGeol6gicas (Chile) and perigee pass over Campo del Cielo in northern in part by National ScienceFoundation grant GP Argentina.A line of meteoritecraters bearing 4521. We thank both these agencies most sin- along azimuth 60ø existsat Campo del Cielo, cerely. and we believe that a large parent meteoroid I•EFERENCES in a terrestrial orbit of minimum size could Cassidy,W. A., L. M. Villar, T. E. Bunch, T. P. have suppliedthe fragmentsthat formed these Kohman, and D. J. Milton, Meteorites and craters and still have survived to make one or craters of Campo del Cielo, Argentina, Science, more additionalpasses through the atmosphere 149(3688), 1055-1064,1965. during succeedingorbits. Minimum orbits of Dence, M. R., The extraterrestrial origin of Ca- nadian craters,Ann. N.Y. Acad. Sci., 125, 941- the earth havea periodof about90 min (shorter 969, 1965. oneswould be deep in the atmosphereor below Fletcher, L., On the meteorites which have been the earth's surface); thereforethe suggested found in the Desert of Atacama and its neigh- second perigee pass would have been made bourhood, Mineral. Mag., 8(40), 223-264, 1889. Innes, M. J. S., Recent advances in meteorite along azimuth 60ø but at least 22 ø west of crater research at the Dominion Observatory, Campodel Cielo (sincethe earth rotates22• ø Ottawa, Canada, Meteoritics, 2(3), 219-241, in 90 min). 1964. The crater reportedhere is only 14ø west of (Manuscript received June 4, 1966; Campo del Cielo, and according to previous revised July 1, 1966.)