Journal Article Multistage formation processes in the acapulcoite-lodranite parent body: Mineralogical study of anomalous lodranite, Yamato 983119

14pp.49 - 59 , 2017-12
Y 983119 is a coarse-grained rock consisting mainly of orthopyroxene (44–71 vol%, Wo3En94Fs4), olivine (4–30 vol%, Fo97), Fe, Ni metal (4–14 vol%) and interstitial plagioclase (9–14 vol%, Or2Ab67An29) and augite (2–5 vol%, Wo46En53Fs2). The modal abundance of orthopyroxene is higher than known acapulcoites and lodranites. Olivine grains show chemical zoning with higher Fe/Mn values along rims and cracks. Orthopyroxene and olivine contain melt inclusions that mainly consist of augite, feldspar and glass. Hornblende, biotite, rutile and baddeleyite were also found in melt inclusions. Based on the compositions of melt inclusions, the parent melt is felsic, and contains a significant amount of Na, K, Ti, Zr, F and OH. The major mineral and oxygen isotopic compositions indicate that Y 983119 is a lodranite. However, the high abundance of orthopyroxene and the presence of melt inclusions indicate that Y 983119 is not a residue in contrast to other lodranites. We suggest that Y 983119 formed by more complex formation processes than the other lodranites.
我々は、南極やまと山脈付近の裸氷帯で発見されたロドラナイト隕石Y 983119の形成史を明らかにするために、岩石鉱物科学的な研究を行った。Y 983119の主要な岩石組織、鉱物化学組成の特徴は、通常のロドラナイト隕石のものと整合的である。一方、Y 983119は、多量な直方輝石、メルト包有物の存在など、通常のロドラナイト隕石には見られない特徴を持つ。これらの結果は、Y 983119が通常のロドラナイト隕石のような溶け残り岩ではないことを示している。我々は、Y 983119がより複雑な形成プロセスによって形成したことを提唱する。

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