05 Classification of.. - Department of Earth and Planetary Sciences

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84 Classification of Meteorites 1.05.5 MARTIAN (SNC) METEORITES 116 1.05.5.1 Shergottites 116 1.05.5.2 Nakhlites (Clinopyroxenites/Wehrlites) 118 1.05.5.3 Chassignite (Dunite) 118 1.05.5.4 Allan Hills 84001 (Orthopyroxenite) 120 1.05.6 LUNAR METEORITES 120 ACKNOWLEDGMENTS 120 REFERENCES 120 1.05.1 INTRODUCTION Solid bodies of extraterrestrial material that penetrate the atmosphere and reach the Earth’s surface are called meteorites. Other extraterrestrial materials include micrometer-sized interplanetary dust particles (IDPs) collected in the lower stratosphere and polar ices. Most meteorites and IDPs are fragments of asteroids, but some IDPs may represent cometary material and some meteorites are fragments of the planets Mars and Earth’s moon. Meteorites recovered following observed falls are called falls; those which cannot definitely be associated with observed falls are called finds. Meteorites are given names based on the location where they were recovered (e.g., the Allende meteorite fell in Allende, Mexico). Meteorites recovered in Antarctica and the deserts of Australia and northern Africa are given names and numbers, because numerous samples are found in the same locations. Fragments thought to be of the same meteorite fall, which, in Antarctica or hot deserts, may have different numbers or even names because they were found in different locations, are called paired. More than 1.7 £ 10 4 meteorites are currently known; this number is rapidly growing through the discovery of large concentrations of meteorites in the cold and hot deserts. Based on their bulk compositions and textures, meteorites can be divided into two major categories, chondrites and nonchondritic meteorites; the latter include the primitive achondrites and igneously differentiated meteorites (Figure 1). They are further classified into groups using a classification scheme based on their oxygen isotopes, chemistry, mineralogy, and petrography (Table 1 and Figure 1). The goals of this classification scheme are to provide descriptive labels for classes of meteorites with similar origins or formation histories that could be derived from the same asteroidal or planetary body, and to reveal possible genetic links between various classes. In this chapter, we describe the existing meteorite classification, classification parameters, and general mineralogical and geochemical characteristics of the meteorite groups. Classification of IDPs and meteorite–asteroid connections are only briefly mentioned; interested readers can find additional Figure 1 Classification of meteorites.
Introduction 85 Table 1 Meteorite groups and numbers of their members. Falls Total Chondrites Carbonaceous CI (Ivuna-like) 5 5 CM (Mighei-like) 15 171 CR (Renazzo-like) 3 78 CO (Ornans-like) 5 85 CV (Vigarano-like) 6 49 CV-oxidized Allende-like CV-oxidized Bali-like CV-reduced CK (Karoonda-like) 2 73 CH (ALHA85005-like) 0 11 CB (Bencubbin-like) CB a : Bencubbin, 0 3 Weatherford, Gujba CB b : QUE94411, 0 2 Hammadah al Hamra 237 Ordinary H 316 6962 L 350 6213 LL 72 1048 Enstatite EH 8 125 EL 7 38 R (Rumuruti-like) 1 19 K (Kakangari-like) 1 3 Ungrouped: Acfer 094 Adelaide Belgica-7904, Yamato-86720, Yamato-82162, Dhofar-225 Coolidge Loongana 001 LEW85332 MAC87300 MAC88107 Ningqiang Tagish Lake Nonchondrites Primitive Acapulcoites 1 12 Lodranites 1 14 Winonaites 1 11 Differentiated (planetary) Achondrites Angrites 1 4 Aubrites 9 46 Brachinites 0 7 HED meteorites Eucrites 25 200 Howardites 20 93 Diogenites 10 94 Ureilites 5 110 Stony-irons Pallasites 5 50 main group pallasites 45 Eagle Station pallasites 3 pyroxene-pallasites 0 2 Mesosiderites 7 66 (continued) Table 1 (continued). Falls Total Irons IAB (nonmagmatic, 5 131 related to IIICD and winonaites) IC 0 11 IIAB 6 103 IIC 0 8 IID 3 16 IIE (related to H chondrites) 1 18 IIF 1 5 IIIAB 11 230 IIICD (nonmagmatic, 3 41 related to IAB and winonaites) IIIE 0 13 IIIF 0 6 IVA 4 64 IVB 0 13 Ungrouped 8 111 Ungrouped nonchondrites ALHA77255 Bocaiuva Deep Springs Divnoe Enon Guin LEW86211 LEW86220 LEW88763 Mbosi Northwest Africa 011 Northwest Africa 176 Puente del Zacate QUE93148 Sahara 00182 Sombrerete Tucson Differentiated (planetary) Martian (SNC): 4 26 Shergottites 2 18 Nakhlites 1 6 (clinopyroxenites/wehrlites) Chassigny (dunite) 1 1 Orthopyroxenite (ALH84001) 0 1 Lunar 0 18 Number of meteorites are from Grady (2000). information in Rietmeijer (1998) and Burbine et al. (2002). Chondrites consist of four major components: chondrules, FeNi-metal, refractory inclusions (Ca–Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)), and fine-grained matrix material. It is generally accepted that the refractory inclusions, chondrules, and FeNi-metal are formed in the solar nebula by high-temperature processes that included condensation and evaporation. Many CAIs and most chondrules and FeNimetal were subsequently melted during multiple brief heating episodes. Matrix, some CAIs, and metal in some chondrites (e.g., CH and CB) appear to have escaped these high-temperature nebular
Page 1: 1.05 Classification of Meteorites A
Page 5 and 6: Classification of Chondritic Meteor
Page 13 and 14: (1992), Rubin et al. (1985), Rubin
Page 17 and 18: Figure 12 Combined elemental maps o
Page 19 and 20: Figure 14 Fayalite (Fa) content (mo
Page 21 and 22: abundances and chondrule sizes by c
Page 23 and 24: Table 6 Synopsis of petrologic char
Page 25 and 26: compositions to the winonaites and
Page 27 and 28: Figure 20 Photomicrographs of brach
Page 29 and 30: Classification of Nonchondritic Met
Page 31 and 32: 1.05.4.4 Pallasites Pallasites are
Page 33 and 34: ,85% of iron meteorites fall into o
Page 35 and 36: Martian (SNC) Meteorites 117 Figure
Page 37 and 38: Martian (SNC) Meteorites 119 Figure
Page 39 and 40: References 121 Benedix G. K., McCoy
Page 41 and 42: References 123 Ivanova M. A., Taylo
Page 43 and 44: References 125 McSween H. Y. Jr. an
Page 45 and 46: References 127 a large differentiat

05 Classification of.. - Department of Earth and Planetary Sciences

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