Computer Science
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28..463y&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 463
Computer Science
Angrites, Fassaite, Olivine, Plagioclase, Xenocrysts
Scientific paper
Both angrite meteorites Lewis Cliff (LEW) 87051 (U.S. collection) and Asuka (A) 881371 (Japanese collection) were collected from Antarctica. The collecting sites of the angrites are Lewis Cliff Ice Tongue, 84 degrees 17 minutes S and 161 degrees OO minutes E in the Transantarctic Mountains, and Asuka Station, 72 degrees 50 minutes S and 24 degrees 30 minutes E, in Queen Maud Land, respectively. Therefore the two localities are separated by almost 2500 km. LEW87051: LEW87051 is 0.6 g in original weight and 1 x 0. 7 x 0.5 cm in diameter; it is a tiny individual achondritic meteorite, completely covered with a black fusion crust [1]. Petrographically, this specimen shows the typical porphyritic texture of olivine with subequal amount of groundmass plagioclase laths and interstitial pyroxene with little opaque. Plagioclase laths, 0.02 x 0.3 mm, are in a subparallel arrangement (Fig. 1). Pyroxene is titanian fassaite showing weak pleochroic of purplish tint, the average composition of which is Wo50.2, containing 6-9% A1203 and 2-6% TiO2, and range En1-29, Fs21-55, and Wo44-53. Olivine contiains variable composition, average Fo21, and ranged Fo8-91 correspond with Fe-rich rim to Mg-rich core. Plagioclase is almost pure anorthite (An99-100). Asuka-881371: A-881371 is 11 g in original weight and 2.0 x 1.6 x 1.6 in diameter. It is a rounded stone almost completely covered with a dull black (not shiny) fusion crust. Pale green, relatively coarse olivine crystals can be seen on the exposed interior surface. Petrographyically, the Asuka angrite shows an unbrecciated and typical ophitic texture with less porphyritic olivine crystal (xenocryst?), and consists mostly of euhedral plagioclase, integranular fassaite, and olivine with traced opaque and spinel (Fig. 2). Pyroxene is titanium fassaite with pleochroic brown in the rim, which is average composition Wo52 containing high CaO (over 22%), A12O3 (3.5-9.9%) and TiO2 (1-5%), and ranged EnO-29, Fs18-50, and Wo48-55. Olivine contains variable composition ranged Fo2.8-90 with Fe-rich rim and extremely Mg-rich core; however, most of the olivine is in the range Fo57-72. Plagioclase is almost pure anorthite (An97-100). Conclusion: Macroscopically, LEW87051 and Asuka angrites are clearly recognized as individual specimens for they are completely covered with a black fusion crust. The great distance between the two localities strongly supports the fact. Therefore, it seems that both angrites have individually fallen on the Antarctic continent and they are not a pair. Nevertheless, both angrites are petrographically very similar, especially their mineralogy and chemical composition, except for some differences in their texture (Figs. 1 and 2). Two angrites LEW87051 and A-881371 seem to have a close genetic relationship on the parent body. LEW87051 and A-881371 angrites are quite difference from Angra dos Reis (ADOR) and LEW86010 angrites from their petrography, mineralogy, and compositions [2,3]. References: [1] Mason B. (1989) Antarctic Meteorite Newsletter 12, No. 1, 15. [2] Printz N. et al. (1977) EPSL, 35, 317-330. [3] Mason B. (1988) Antarctic Meteorite Newsletter 10, No. 2, 32 .
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