NWA 10214—An LL3 chondrite breccia with an assortment of metamorphosed, shocked, and unique chondrite clasts

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• 作者：Alan E. Rubin ; John P. Breen ; Junko Isa and Sean Tutorow
• 刊名：Meteoritics & Planetary Science
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：52
• 期：2
• 页码：372-390
• 全文大小：1724K
• ISSN：1945-5100

文摘

NWA 10214 is an LL3-6 breccia containing ~8 vol% clasts including LL5, LL6, and shocked-darkened LL fragments as well as matrix-rich Clast 6 (a new kind of chondrite). This clast is a dark-colored, subrounded, 6.1 × 7.0 mm inclusion, consisting of 60 vol% fine-grained matrix, 32 vol% coarse silicate grains, and 8 vol% coarse opaque grains. The large chondrules and chondrule fragments are mainly Type IB; one small chondrule is Type IIA. Also present are one 450 × 600 μm spinel-pyroxene-olivine CAI and one 85 × 110 μm AOI. Clast 6 possesses a unique set of properties. (1) It resembles carbonaceous chondrites in having relatively abundant matrix, CAIs, and AOIs; the clast's matrix composition is close to that in CV3 Vigarano. (2) It resembles type-3 OC in its olivine and low-Ca pyroxene compositional distributions, and in the Fe/Mn ratio of ferroan olivine grains. Its mean chondrule size is within 1σ of that of H chondrites. The O-isotopic compositions of the chondrules are in the ordinary- and R-chondrite ranges. (3) It resembles type-3 enstatite chondrites in the minor element concentrations in low-Ca pyroxene grains and in having a high low-Ca pyroxene/olivine ratio in chondrules. Clast 6 is a new variety of type-3 OC, somewhat more reduced than H chondrites or chondritic clasts in the Netschaevo IIE iron; the clast formed in a nebular region where aerodynamic radial drift processes deposited a high abundance of matrix material and CAIs. A chunk of this chondrite was ejected from its parent asteroid and later impacted the LL body at low relative velocity.