A new Martian meteorite from Morocco: the nakhlite North West Africa 817 V. Sautter a; *, J.A. Barrat b , A. Jambon c , J.P. Lorand a , Ph. Gillet d , M. Javoy e , J.L. Joron f , M. Lesourd g a Laboratoire de Mine ¨ralogie, FR32-CNRS, Muse ¨um National d'Histoire Naturelle, 61 rue Bu¡on, 75005 Paris, France b CNRS-UMR 6112 (Ge ¨odynamique et Plane ¨tologie) and Universite ¨ d'Angers, 2 bd Lavoisier, 49045 Angers Cedex, France c Laboratoire Magie, Universite ¨ Pierre et Marie Curie, UMR-CNRS 7047 case 110, 4 place Jussieu, 75252 Paris Cedex 05, France d Laboratoire des Sciences de la Terre, CNRS-UMR 5570, Ecole Normale Supe ¨rieure de Lyon, 46 Alle ¨e d'Italie, 69364 Lyon Cedex 7, France e Laboratoire de Ge ¨ochimie des Isotopes Stables, Universite ¨ de Paris VII, Institut de Physique du Globe et UMR-CNRS 7047, 4 Place Jussieu, 75251 Paris Cedex 05, France f Laboratoire Pierre Sue, CEA-CNRS, Saclay, 91191 Gif sur Yvette, France g CNRS et SCIAM, 2 rue Haute de Recule ¨e, F-49045 Angers, France Received 13 July 2001; received in revised form 22 October 2001; accepted 27 October 2001 Abstract North West Africa (NWA 817) is a single stone of 104 g found in the Sahara (Morocco) by meteorite hunters in November 2000. The meteorite is an unbrecciated, medium-grained olivine-bearing clinopyroxenite with a cumulate texture. It consists of zoned euhedral subcalcic augite (Wo 42 En 3822 Fs 2036 ), olivine spanning a wide range of compositions (from Fa 56 in the core to Fa 86 ) with rare magmatic inclusions and an intercumulus mesostasis made of Fe- bearing albitic plagioclase, Si-rich glass, Ti-magnetite with unusual skeletal growth morphologies containing ilmenite exsolutions, acicular pyroxene, olivine and cristobalite. Trace minerals are sulfide droplets and Cl-apatite. Mineral modes (in vol%) are augite 69%, olivine 10%, mesostasis 20% and Fe^Ti oxides 1%. Pervasive alteration produced a reddish clay mineral (hydrous ferrous silicate) in both olivine crystals and the mesostasis. The major element composition of NWA 817 is very similar to that of the other nakhlites: high FeO, MgO and CaO concentrations reflect the abundance of cumulus augite and olivine. Key element ratios such as FeO/MnO ( = 37), Na/Al ( = 0.40), K/La ( = 449), Ga/Al ( = 3.9U10 34 ) and oxygen isotopic composition (v 17 O = +0.37x) are clear evidence for a Martian origin. The incompatible trace element pattern as in Nakhla displays a strong light rare earth element enrichment relative to chondrite (La n /Yb n = 4.89). However, when compared to the other nakhlites, NWA 817 has specific features : (1) a higher modal proportion of mesostasis; (2) quench textures of Ti-magnetite and Fe-rich clinopyroxene; (3) more Mg-rich olivine core compositions whereas the augite core composition is identical for all nakhlites ; (4) a stronger Fe enrichment toward crystal rims of these cumulus minerals. The intercumulus minerals (Ti-magnetite with skeletal growth morphology, acicular chains of clinopyroxene and Fe 3 -rich feldspar) indicate rapid crystallization in response to a high degree of undercooling at the end of the sample story. ß 2002 Elsevier Science B.V. All rights reserved. 0012-821X / 02 / $ ^ see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII:S0012-821X(01)00591-X * Corresponding author. Tel.: +33-1-40793525; Fax: +33-1-40793524. E-mail address: sautter@mnhn.fr (V. Sautter). Earth and Planetary Science Letters 195 (2002) 223^238 www.elsevier.com/locate/epsl