Petrogenesis of Alta'ameem meteorite (Iraq) inferred from major, trace, REE and PGE+Au content
Abstract Alta'ameem Meteorite (AM) is an unaltered ordinary LL chondrite that hit an area near Kirkuk City in northern Iraq on 1977. It has an ash-gray colour with a thin black fusion crust, and consists of spheroidal chondrules and variously shaped clasts aggregated together by a fine grained matrix. The chondrules of Alta'ameem Meteorite include all known types in similar meteorites elsewhere. Mineralogically, the AM consists of silicates (olivine - Fa 27.7 ; pyroxene - Fs 23.2 (Opx) and 20.5 (Cpx) ; plagioclase - Ab 73.5 An 22.1 Or 4.7 ), alloys and metals (taenite, tetrataenite, kamacite, and native copper), oxides (ilmenite and chromite), sulfides (troilite), and phosphates (apatite) as well as few unidentified minerals including a Fe-Ti-Cr oxide and Fe-Ni sulfide. The chemistry of AM is dominated by SiO 2 , MgO, and FeO t accounting for >91 wt% of the bulk composition with minor amounts of Al 2 O 3 , CaO, Na 2 O, S, Ni and Cr. It contains 3675 ppb REE which is within the range of most chondrites, with a negative (−0.8) Sm- and positive (+1.2) Tb-anomalies and a near flat normalized trend (La N /Yb N = 1.16). The concentration of PGEs and Au, Ni, Co, and Cr is low in comparison to most chondrites. The K/La, Ru/Rh vs. Pt/Pd, and Pd/Ir ratio (1.85), and low PGE indicates that the AM is somewhat distinct from other meteorites. The AM has W0 weathering grade and very weak (S2) shock metamorphism. Although the AM has some petrographical and geochemical differences with other chondrites, it still can be considered as LL5 chondrite. Highlights Alta'ameem Meteorite (AM) is a LL5 chondrite that hit northern Iraq on 1977. Th AM is studied petrographically, mineralogically and geochemically. The AM contains silicates, native metals, Fe-Ni alloys, sulfides, phosphates & oxides. The predominant minerals in AM are olivine, pyroxene and minor plagioclase. The AM is richer in LILE and poorer in HSE relative to average LL-chondrites. Graphical abstract [DISPLAY OMISSION]
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- DOI : http://dx.doi.org/10.1016/j.jafrearsci.2017.11.015
- Elsevier : 저널 > 논문
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