Abstract

In the last 10 years the Chilean meteorite collection become the biggest in South America [1] due to systematical search done by a collaborative Chilean-French team that rise the number from ~60 to ~500 and that it is still finding many more each year [2, 3]. The Chilean Geological Survey (SERNAGEOMIN) is the main governmental institution in Chile dedicated to build the geological information of the territory, and from 2010 is carrying out an exhaustive mapping program (Plan Nacional de Geología) to cover most of the territory to the scale 1:100.000. In this context, at least five teams are mapping the surfaces of the Atacama Desert, and two teams, just by chance, in different field trips on 2013, found the meteorites we present here, that resulted to be part of the same groups of meteorites submitted to the Nomenclature Committee by the name El Médano. Results: The samples correspond to equilibrated ordinary chondrites that have preserved their fusion crust, indicating that little or negligible mechanic erosion has occurred, of masses of 407.90 g and 48.02 g. We first classified them using petrographic and magnetic susceptibility criteria according to [4], [5], [6], and [7] as a H6 S3 W1 and a H3 or 4 S2 W1, respectively, confirming this preliminary classification with microprobe data, that resolve also the metamorphic grade to be type 4 for the 48,02g meteorite. We did also X ray diffraction analysis to have a better characteri- zation of the primary and secondary mineralogy, complementary to the petrographic descriptions. Taking into consideration the fortuitous character of these findings, adding the climatic, geological and geomorphological conditions of this area, we believe that it is highly possible to keep finding meteorites there in our future missions, and also in other areas of study in the Atacama Desert. It is our idea to include a protocol of searching when we are mapping suitable areas for meteorite recovery to improve the col- lection, and also incorporate the information related to the ages of the surfaces from the terrestrial ages of the meteorites and from the density of micrometeorites, as have been pointed by [8] and [9], that will improve the knowledge of the geomorphological context of these old Pampas, and enrich the information of the geological maps. References: [1] http://www.lpi.usra.edu/meteor/metbull.php [2] Valenzuela, 2011. PhD thesis, Universidad de Chile, 201 p. [3] Gattacceca J. et al. 2011. Meteoritics and Planetary Science 9:1276- 1287. [4] Van Schmus W. R. and Wood J. A. 1967. Geochimica et Cosmochimica.Acta 31:747-765. [5] Stöffler D. et al. 1991. Geochi- mica et Cosmochimica Acta 55:3845-3867. [6] Wlotzka F. 1989. Me- teoritical Bulletin No. 68. Meteoritics 24, 57. [7] Rochette P. et al. 2012. Meteorites Vol 2, Nos 1-2, 67-71. [8] Rochette P. et al. 2008. Proceedings of the National Academy of Sciences of the United States of America Vol. 105, 47:18206-18211. [9] Rochette P. et al. 2011. Met.Soc. Meeting, abstract #5038.