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Méthodologie D'étude Des Météorites Du Maroc Methodology of Studying

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Méthodologie D'étude Des Météorites Du Maroc Methodology of Studying Bulletin de l’Institut Scientifique, Rabat, Section Sciences de la Terre, 2014, n° 36, 00-00. Méthodologie d’étude des météorites du Maroc Methodology of studying meteorites from Morocco Nawel LAROUCI1*, Hassna CHENNAOUI AOUDJEHANE1, Albert JAMBON2 1. Université Hassan II Casablanca, Faculté des Sciences Aïn Chock, Laboratoire GAIA, Equipe : patrimoine géologique du Maroc *([email protected]). 2. Université Pierre et Marie Curie, ISTeP UMR 7193, Paris, France. Résumé. La contribution scientifique des météorites provenant du Maroc est sans égal. Leur classification a été une réponse à une nécessité commerciale plus qu’à des considérations scientifiques. Développer une méthodologie éthique et scientifique pour l’étude de ces objets extraterrestres apparaît aujourd’hui comme une nécessité. Il convient de lutter contre les classifications approximatives des météorites provenant du Maroc en général, et la nomenclature «Northwest Africa (NWA)» en particulier. La méthodologie d’étude des météorites du Maroc, proposée dans ce travail comprend trois étapes : 1) Collecte d’informations sur le terrain suivant un questionnaire détaillé. Cette étape est indispensable pour toute étude de chute ou trouvaille, elle renseigne sur l’observation éventuelle d’un bolide, ainsi qu’un certain nombre de critères concernant l’échantillon collecté. Ces informations sont nécessaires pour l’attribution du nom de lieu officiel à toute météorite étudiée. 2) Etude pétrographique et géochimique de l’échantillon : cette étape fondamentale, permet la classification de la météorite. 3) Déclaration de l’échantillon auprès du comité de nomenclature (NomCom) de la «Meteoritical Society», avec des coordonnées précises et un nom de lieu, afin d’officialiser la météorite sur le plan scientifique international et de contribuer à l’enrichissement de la production scientifique qui les concerne. Le NomCom a la responsabilité de soutenir une démarche de documentation solide pour toute nouvelle trouvaille. Les scientifiques ont la responsabilité de léguer aux générations futures un patrimoine aussi bien documenté que possible. Mots-clés : Météorites, pétrographie, géochimie, classification, déclaration, Maroc. Abstract. The scientific input of meteorites from Morocco is outstanding. Their classification was a response to commercial needs than scientific considerations. We are concerned by developing an ethical and scientific study protocol of meteorites recovered in Morocco. The Northwest Africa (NWA) nomenclature has accepted the absence of documentation for numerous meteorites from Morocco. In this paper, we present an ethical and scientific methodology to the study of these extraterrestrial objects in order to avoid approximate classifications of meteorites from Morocco, especially the Northwest Africa (NWA) nomenclature. The recommended approach consists of three steps: 1) Collection of field information, following a detailed question list: This step is the essential for any falls or finds of meteorites. It provides information on the possible observation of a meteor, and on a number of criteria, that concern the collected sample, 2) Petrographic and geochemical study of the sample. This fundamental step allows the classifications of the meteorite, 3) Declaration of the meteorite sample with precise coordinates and location name to the Nomenclature Committee (NomCom) of the Meteoritical Society, in order to formalize internationally the new founded meteorite, and contribute to the enrichment of the scientific production related to this meteotite. The NomCom should support and promote every attempt to secure the scientific documentation of new finds in Morocco, and scientists are responsible to hand for future generations, as possible as they can, an accurate scientific documentation of the finds. Keywords : Meteorites, petrography, geochemistry, classification, declaration, Morocco. Abridged English version countries in the world in terms of meteorites finds. Up to Introduction date, many falls and finds were collected and studied. They delivered and continue to deliver an invaluable amount of Morocco is the country where the largest share of information about the origin and evolution of our solar meteorites has been found, particularly the rare types. system. We can separate meteorites «falls» (with eye- Therefore, they are highly coveted by collectors and witnesses) from «finds». scientists around the world. In the absence of stringent laws, the anarchic exploitation of these "stones falling from the All meteorites from Morocco and surrounding countries sky" accelerates the loss of the geoheritage of Moroccan are named after the acronym Northwest Africa «NWA», meteorites. Also, beyond the interest and scientific curiosity followed by a number (Grossman 2000; Chennaoui et al. aroused by meteorites, collecting these space rocks appears 2013, 2014). to be an important source of income for some hunters and Currently, there are over 8058 NWA meteorites and traders. For these reasons, it becomes necessary to develop only 978 were recognized from Morocco (Meteoritical a protocol for the study of meteorites from Morocco to line Bulletin Database, February 02, 2015). Only 25 finds from up with the scientific progress in this area. Morocco carry a locality name. There are also 11 witnessed falls from Morocco, classified mostly by our laboratory. History and study of meteorites from Morocco A number of meteorites from Morocco are of great The Moroccan territory is a privileged place for scientific value, among those: collection of meteorites due to its extended desert area - The observed falls: Tissint, Martian meteorite through which, Morocco has become one of the richest Shergottite type (Chennaoui Aoudjehane et al. 2012), and 00 Larouci et al. – Méthodologie d’étude des météorites du Maroc Tirhert, Eucrite type. Several falls of ordinary chondrites stage is the classification. The classification of most were also observed: Benguerir (Chennaoui Aoudjehane et meteorites is straightforward (Fig. 1), however a small al. 2006a) and Tamdakht (Chennaoui Aoudjehane et al. number of the finds is problematic. Discrimination between 2009a). However, there are observed falls where no samples some achondrites and terrestrial rocks is sometimes difficult have been recovered, like the fall of the November 15, 2009 and time consuming. In particular, recognition new in Nzala region (Eastern Region of Morocco). meteorite types that usually correspond to the most valuable - Finds of achondrites: Oued Awlitis 001 one of the 86 finds (both scientifically and economically) must definitely out of 202 lunar meteorites, 670 of 1550 HEDs (e.g. Barrat be accurate. A such example is identifying a Martian rocks et al. 2003), 17 out of 23 recorded angrites (e.g. Jambon et with non-Martian oxygen isotopes, like NWA 7034. al. 2005, 2008), 171 out of 395 Ureilites (e.g. Le Guillou et al. 2010) and 83 out of 144 Martians meteorites: among The Meteoritical Bulletin (Met Bull) Publication those NWA 7034 (Agee et al. 2013; Jambon et al. 2002, 2003, 2010; Sautter et al. 2006). The publication of a new find of meteorite is of great importance for scientists and for dealers, especially when The study of meteorites from Morocco consists in the meteorite is of an important economical value. This is a several steps ranging from: collecting information on the necessary step after studying a new meteorite (fall or find) field, to the classification and reporting to the Nomenclature that should be done as quickly as possible. The declaration Committee (NomCom) of the Meteoritical Society should be submitted to the NomCom as an excel (MetSoc, www.meteoriticalsociety.org/). The rare types of spreadsheet listing different criteria (place of collect, meteorites are subject to more insightful research. petrography, geochemistry, weight and number of pieces collected...). The proposed name of the new meteorite is Falls: Eyewitness / geographic coordinates one of the problems for which our laboratories have been Collecting field information is of utmost importance, struggling in recent years. The acronym "NWA" has been considering the significant number of falls and the poor granted for a large number of finds, since their coordinates treatment of those submitted as NWA. Some samples are are imprecise (a practice introduced in 2000: Grossman still considered in the database as finds, not falls. A 2000, Chennaoui et al. 2013, 2014). questionnaire concerns a number of key criteria including: Geographic names are preferable whenever coordinates contact details of the witness, date, place and direction of are provided. All hunters, dealers and scientists must be the fall, height and color of the bolide, potential obstacles to encouraged to document the find location. NWA should be the end of observation, noises heard, as well as other understood as a rubble pile for people unable to work questions related to the observation of the phenomenon to properly. Giving NWA numbers to documented finds is a finally find the exact coordinates of the fall. One key disaster because it does not make difference between measurement is short-lived radiogenic isotopes, which is the fraudulent finds (i.e. exported from places where collecting only unambiguous way to prove a recent fall. meteorites is illegal) and valuable finds with proper documentation. In addition, having reliable find coordinates Petrographic, geochemical study and classification of a is important for sample pairing, in the case of rare finds meteorite (typically, lunar,
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