Petrology, geochemistry, and cosmic-ray exposure age of lherzolitic shergottite Northwest Africa 1950

available online at http://meteoritics.org 1175 © The Meteoritical Society, 2005. Printed in USA. Petrology, geochemistry, and cosmic-ray exposure age of lherzolitic shergottite Northwest Africa 1950 P. GILLET1*, J. A. BARRAT2, P. BECK1, B. MARTY3, R. C. GREENWOOD4, I. A. FRANCHI4, M. BOHN5, and J. COTTEN6 1Laboratoire des Sciences de la Terre, CNRS UMR 5570, Ecole Normale Supérieure de Lyon, 46 Allée d’Italie, 69364 Lyon Cedex 7, France 2Domaines Océaniques, CNRS UMR 6538 U.B.O.-I.U.E.M., place Nicolas Copernic, 29280 Plouzané Cedex, France 3CRPG-CNRS UPR 2300, 15 rue Notre-Dame des Pauvres, 54501 Vandoeuvre-lès-Nancy Cedex, France 4Planetary and Space Science Research Institute, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK 5Ifremer-Centre de Brest, CNRS-UMR 6538, BP70, 29280 Plouzané Cedex, France 6Université de Brest, C.N.R.S. UMR 6538, 6 avenue Le Gorgeu, 29100 Brest, France *Corresponding author. E-mail: [email protected] (Received 03 March 2005; revision accepted 06 July 2005) Northwest Africa (NWA) 1950 is a new member of the lherzolitic shergottite clan of the Martian meteorites recently found in the Atlas Mountains. The petrological, mineralogical, and geochemical data are very close to those of the other known lherzolitic shergottites. The meteorite has a cumulate gabbroic texture and its mineralogy consists of olivine (Fo66 to Fo75), low and high-Ca pyroxenes (En78Fs19Wo2En60Fs26W14; En53Fs16Wo31-En45Fs14Wo41), and plagioclase (An57Ab41Or1 to An40Ab57Or3; entirely converted into maskelynite during intense shock metamorphism). Accessory minerals include phosphates (merrillite), chromite and spinels, sulfides, and a glass rich in potassium. The oxygen isotopic values lie on the fractional line defined by the other SNC meteorites (∆17O = 0.312 ‰). The composition of NWA 1950 is very similar to the other lherzolitic shergottites and suggests an origin from the same magmatic system, or at least crystallization from a close parental melt. Cosmogenic ages indicate an ejection age similar to those of the other lherzolitic shergottites. The intensity of the shock is similar to that observed in other shergottites, as shown by the occurrence of small melt pockets containing glass interwoven with stishovite.