A new type of solar-system material recovered from Ordovician marine limestoneOPEN ACCESS
B. Schmitz, Q. -Z. Yin, M. E. Sanborn,M. Tassinari,C. E. Caplan & G. R. Huss
Nature Communications 7,
Article number:ncomms11851
doi:10.1038/ncomms11851
Published 14 June 2016
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“From mid-Ordovician ~470 Myr-old limestone >100 fossil L-chondritic meteorites have been recovered, representing the markedly enhanced flux of meteorites to Earth following the breakup of the L-chondrite parent body. Recently one anomalous meteorite, Österplana 065 (Öst 65), was found in the same beds that yield L chondrites. The cosmic-ray exposure age of Öst 65 shows that it may be a fragment of the impactor that broke up the L-chondrite parent body. Here we show that in a chromium versus oxygen-isotope plot Öst 65 falls outside all fields encompassing the known meteorite types. This may be the first documented example of an ‘extinct’ meteorite, that is, a meteorite type that does not fall on Earth today because its parent body has been consumed by collisions. The meteorites found on Earth today apparently do not give a full representation of the kind of bodies in the asteroid belt ~500 Myr ago.”
The meteorite is 8 × 6.5 × 2 cm large. It is surrounded by a grey reduction halo, in the otherwise red limestone. Oxygen was consumed when the meteorite weathered on the sea floor. The coin in the image has a diameter of 2.5 cm.
Comparison of Δ17O versus ε54Cr of achondrites, and ordinary chondrites fallen on Earth in recent time with Österplana 065 (Öst 65) and fossil L-chondritic meteorites Österplana 018, 029 and 032 (Öst 18, Öst 29 and Öst 32 in figure). The fields for ordinary chondrites (OC), Mars (SNCs), Earth and earth-likes, Vesta (HEDs), brachinites, ureilites, winonaites (win), acapulcoites (acp)/lodranites/ungrouped achondrites (ung) and a newly identified unique metal-rich chondrite are marked with select representative samples with available data. Symbol colours indicate meteorite type or grouping. Note that the carbonaceous chondrites and affiliated achondrites plot outside the field, with highly positive ε54Cr.
(a) Chrome-spinel grain with inclusion of a TiCr-mineral, possibly olkhonskite (TiO2=56 wt%, Cr2O3=30 wt%, FeO=9 wt%). (b) Rutile and chrome spinel in polished section of Öst 65. (c) Chrome-spinel grain with apparent shock deformation lamellae. Scale bars, 50 μm.
