The densest meteorite collection area in hot deserts: The San Juan meteorite field (Atacama Desert, Chile)

Abstract-One of the most productive and well-sampled dense collection areas for meteorites on Earth is the "Franconia strewn field" in Mohave County, Arizona, which since 2002 has yielded hundreds of meteorites in an ellipsoidal area approximately 5 9 16 km across. Based on petrographic, mineral-chemical, and terrestrial age data, we conclude that among 14 meteorites examined, there are at least 6 and possibly 8 distinct meteorites represented, which fell over a period of approximately 0-20 kyr ago. These include equilibrated H-chondrites such as Franconia (H5) and Buck Mountains (BM) 001 (H6); H3-6 breccias such as Buck Mountains Wash and BM 004; and L6 chondrites such as BM 002 and BM 003 (which may be paired), Palo Verde Mine, and BM 005. To confidently pair such meteorites often requires thorough petrographic examination, mineral-chemical analyses, and terrestrial ages. We estimate that 50 AE 10% of the larger specimens in this area are paired, yielding a relatively high value of approximately 2.3-2.9 distinct meteorites km À2 . The meteorite flux estimated for Franconia area is higher than the flux inferred from contemporary fireball data for larger masses. We suggest that one large H3-6 meteoroid fell in the area, most likely that of Buck Mountains Wash approximately 4 kyr ago, which produced an elliptical strewn field with masses generally increasing toward one end, and which raised the meteorite productivity in the recovery area.

Section: Discussionmentioning

confidence: 93%

Stones from Mohave County, Arizona: Multiple falls in the “Franconia strewn field”

Hutson

Ruzicka

Jull

et al. 2013

“…Then, the model computes the geometric mean of those factors and validates the pairing if the result is high enough—the minimal value having been calibrated using pre‐existing collections that have been paired already (here we used the collection of San Juan DCA, in Gattacceca et al. ).…”

Section: Pairingmentioning

confidence: 99%

“…However, as shown in Gattacceca et al. (), it is a very promising place for meteorite recovery, with locally high meteorite concentrations, estimated for instance to 14 unpaired meteorites per km 2 in the San Juan dense collection area (DCA). This density is at least one order of magnitude larger than the one estimated in Oman or Libya, for example (Schlüter et al.…”

Section: Introductionmentioning

confidence: 99%

Description of a very dense meteorite collection area in western Atacama: Insight into the long‐term composition of the meteorite flux to Earth

Hützler

Gattacceca

Rochette

et al. 2016

Self Cite

International audience–We describe the geological, morphological, and climatic settings of two new meteorite collections from Atacama (Chile). The " El M edano collection " was recovered by systematic on-foot search in El M edano and Caleta el Cobre dense collection areas and is composed of 213 meteorites before pairing, 142 after pairing. The " private collection " has been recovered by car by three private hunters and consists of 213 meteorites. Similar to other hot desert finds, and contrary to the falls and Antarctica finds, both collections show an overabundance of H chondrites. A recovery density can be calculated only for the El M edano collection and gives 251 and 168 meteorites larger than 10 g km À2 , before and after pairing, respectively. It is by far the densest collection area described in hot deserts. The Atacama Desert is known to have been hyperarid for a long period of time and, based on cosmic-ray exposure ages on the order of 1–10 Ma, to have been stable over a period of time of several million years. Such a high meteorite concentration might be explained invoking either a yet unclear concentration mechanism (possibly related to downslope creeping) or a previously underestimated meteorite flux in previous studies or an average terrestrial age over 2 Myr. This last hypothesis is supported by the high weathering grade of meteorites and by the common terrestrial fragmentation (with fragments scattered over a few meters) of recovered meteorites

“…We used the pairing proposed by Gattacceca et al. (), that resulted in six meteorites being paired (see Table ). However, in our study, the frequency histograms of oxidation show no significant difference with or without pairing.…”

Section: Experimental Methodsmentioning

confidence: 99%

Weathering of ordinary chondrites from the Atacama Desert, Chile, by Mössbauer spectroscopy and synchrotron radiation X‐ray diffraction

Munayco¹,

Munayco²,

Avillez

et al. 2013

Self Cite

Abstract-Some terrestrial areas have climatic and geomorphologic features that favor the preservation, and therefore, accumulation of meteorites. The Atacama Desert in Chile is among the most important of such areas, known as DCA. This desert is the driest on Earth, one of the most arid, uninhabitable localities with semiarid, arid, and hyper-arid conditions. The meteorites studied here were collected from within the DCA of San Juan and Pampa de Mejillones, located, respectively, in the Central Depression and the Coastal Range of the Atacama Desert.57 Fe M€ ossbauer spectroscopy was used for quantitative analysis of the degree of weathering of the meteorites, through the determination of the proportions of the various Fe-bearing phases and in particular the amount of oxidized iron in terrestrial alteration products. The abundance of ferric ions in weathered chondrites can be related to specific precursor compositions and to the level of terrestrial weathering. The aim of the study was the identification, quantification, and differentiation of the weathering products in the ordinary chondrites found in the San Juan and the Pampa de Mejillones areas of the Atacama Desert. The 57 Fe M€ ossbauer spectroscopy study was complemented by synchrotron radiation X-ray diffraction and magnetic susceptibility measurements. The results allow a clear differentiation of the rate of weathering in meteorite samples collected from the San Juan versus the Pampa de Mejillones areas of the Atacama Desert.