ORIGIN OF LOW-CA PYROXENE IN AMOEBOID OLIVINE AGGREGATES: EVIDENCE FROM OXYGEN ISOTOPIC COMPOSITIONS
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dc.contributor.author | Krot A.N. | |
dc.contributor.author | Fagan T.J. | |
dc.contributor.author | Nagashima K. | |
dc.contributor.author | Yurimoto H. | |
dc.contributor.author | Petaev M.I. | |
dc.date.accessioned | 2023-12-03T03:59:56Z | |
dc.date.available | 2023-12-03T03:59:56Z | |
dc.date.issued | 2005 | |
dc.identifier | https://www.elibrary.ru/item.asp?id=14674509 | |
dc.identifier.citation | Geochimica et Cosmochimica Acta, 2005, 69, 7, 1873-1881 | |
dc.identifier.issn | 0016-7037 | |
dc.identifier.uri | https://repository.geologyscience.ru/handle/123456789/42105 | |
dc.description.abstract | Amoeboid olivine aggregates (AOAs) in primitive carbonaceous chondrites consist of forsterite (Fa<2), Fe,Ni-metal, spinel, Al-diopside, anorthite, and rare gehlenitic melilite (Åk<15). ~10% of AOAs contain low-Ca pyroxene (Fs1–3Wo1–5) that is in corrosion relationship with forsterite and is found in three major textural occurrences: (i) thin (<15 μm) discontinuous layers around forsterite grains or along forsterite grain boundaries in AOA peripheries; (ii) 5–10-μm-thick haloes and subhedral grains around Fe,Ni-metal nodules in AOA peripheries, and (iii) shells of variable thickness (up to 70 μm), commonly with abundant tiny (3–5 μm) inclusions of Fe,Ni-metal grains, around AOAs. AOAs with the low-Ca pyroxene shells are compact and contain euhedral grains of Al-diopside surrounded by anorthite, suggesting small (10%–20%) degree of melting. AOAs with other textural occurrences of low-Ca pyroxene are rather porous. Forsterite grains in AOAs with low-Ca pyroxene have generally ¹⁶O-rich isotopic compositions (Δ¹⁷O < −20‰). Low-Ca pyroxenes of the textural occurrences (i) and (ii) are ¹⁶O-enriched (Δ¹⁷O < −20‰), whereas those of (iii) are ¹⁶O-depleted (Δ¹⁷O = −6‰ to −4‰). One of the extensively melted (>50%) objects is texturally and mineralogically intermediate between AOAs and Al-rich chondrules. It consists of euhedral forsterite grains, pigeonite, augite, anorthitic mesostasis, abundant anhedral spinel grains, and minor Fe,Ni-metal; it is surrounded by a coarse-grained igneous rim largely composed of low-Ca pyroxene with abundant Fe,Ni-metal-sulfide nodules. The mineralogical observations suggest that only spinel grains in this igneous object were not melted. The spinel is ¹⁶O-rich (Δ¹⁷O ∼ −22‰), whereas the neighboring plagioclase mesostasis is ¹⁶O-depleted (Δ¹⁷O ∼ −11‰). | |
dc.subject | Amoeboid olivine aggregates | |
dc.subject | chondrites | |
dc.subject | low-Ca pyroxene | |
dc.title | ORIGIN OF LOW-CA PYROXENE IN AMOEBOID OLIVINE AGGREGATES: EVIDENCE FROM OXYGEN ISOTOPIC COMPOSITIONS | |
dc.type | Статья | |
dc.identifier.doi | 10.1016/j.gca.2004.06.046 |
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