Bland, PA

Morata, D

Roeschmann, C

Russell, SS

Valenzuela, EM

Meteoritics and Planetary Science

Spiral - Imperial College Digital Repository

CHONDRITES FROM THE ATACAMA DESERT E. M. Valenzuela 1, P. A. Bland2, S. S. Russell3, C. Roeschmann1 and D. Morata1. 1Departamento de Geología, Fac. Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile. E-mail: edvalenz@cec.uchile.cl. 2Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, UK. 3Department of Mineralogy, The Natural History Museum, London SW7 5BD, UK.  Introduction: The Atacama Desert in northern Chile, South America, is one of the driest deserts on Earth [1]. Its age is about 15 Mys and the arid conditions were established around the Middle Miocene [2], with some more humid cycles in the Holocene [3]. Its extreme aridity and the presence of vast ablation surfaces have allowed the preservation of meteorites of unknow terrestrial ages. At present, there are 67 meteorites registered. From this list, 15 are chondrites, collected from three main areas. Recent studies [4, 5, 6] carried out on meteorites from other deserts - Australia, Africa and North America - have shown important relations between their terrestrial age and the weathering stage of their primary mineralogy. These data give some clues on terrestrial processes, that in some cases have been strongly influenced by climatic or geomorphologic conditions at the accumulation sites. In the same way, Atacama Desert chondrites can contribute to the understanding of terrestrial weathering processes acting on meteorites and also on terrestrial surfaces. Past studies: Until now, most chondrites have not been analysed beyond a basic classification. Only [7] reports a complete petrological and geochemical study from Paposo, a LL ordinary chondrite showing unusually Fe-rich olivines and pyroxenes, (Fa 333 333-Fs27, respectively), an enriched LREE pattern (LaN=3,381, CeN=2,833, normalized to CI) and weathering products as akaganéite, goethite and maghemite. One of the recovery surfaces, a plain of about 750km2, appears to be a great accumulation site with samples from at least three different falls, inferred from some preliminary terrestrial ages [8] Present Studies: Some of the studies that will be performed with these chondrites are measurement of 14C and 36Cl terrestrial ages, 57Fe Mössbauer spectroscopy (to quantify the degree of oxidation in samples) and petrologic and geochemical analyses. From terrestrial ages and oxidation-frequency distributions for populations of samples we expect to estimate the ages of some Atacama Desert surfaces, as well as to impose constraints on the effect of climate on rock weathering rates between different sites from the differences in the weathering rate of samples. We also hope to contribute to the understanding of the Atacama Desert paleoclimatic evolution during the last 50 kys, studying the structure in the oxidation–terrestrial age distribution for meteorites from these accumulation sites. References: [1] Navarro-González R. et al. 2003. Science 302: 1018-1021 [2] Alpers C.N. and Brimhall G.H. 1988. Geological Society of America Bulletin 100:1640-1656. [3] Grosjean M. et al, 2003. Palaeogeography, Palaeoclimatology, Palaeoecology 194:247-258. [4] Bland P.A. et al. 1998. Geochimica et Cosmochimica Acta 62:3169-3184. [5] Bland P.A. et al. 2000. Quaternary Research 53, 131–142. [6] Jull A. J. T. 1995. Lunar and Planetary Institute Technical Report 95-02: 37–38. [7] Valenzuela E.M. et al. 2003. Extended Abstract Volume of the X Congreso Geológico Chileno. [8] Jull A.J.T. 2005. Personal communication.  68th Annual Meteoritical Society Meeting (2005) 5096.pdf

Chondrites from the Atacama Desert

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