Fossiler Winonait-ähnlicher Meteorit im Ordovizium-Kalkstein (Thorsberg)

[karmaka]

Erster fossiler Winonait-ähnlicher Meteorit im Ordovizium-Kalkstein des Thorsberg-Steinbruchs in Schweden gefunden

A fossil winonaite-like meteorite in Ordovician limestone: A piece of the impactor that broke up the L-chondrite parent body?
Schmitz et al.

Earth and Planetary Science Letters 400:145.
[doi:10.1016/j.epsl.2014.05.034]

FOTO

LINK

Supplementary Material (PDF)

Highlights
• The first non-L-chondritic fossil meteorite in Ordovician limestone has been found.
• It is of a type not previously known to science, but similar to the rare winonaites.
• It may represent a fragment of the body that broke up the L-chondrite parent body.
• The meteorite flux in the Ordovician appears to have been very different from today.

About a quarter of all meteorites falling on Earth today originate from the breakup of the L-chondrite parent body ~470 Ma ago, the largest documented breakup in the asteroid belt in the past ~3 Ga. A window into the flux of meteorites to Earth shortly after this event comes from the recovery of about 100 fossil L chondrites (1–21 cm in diameter) in a quarry of mid-Ordovician limestone in southern Sweden. Here we report on the first non-L-chondritic meteorite from the quarry, an 8 cm large winonaite-related meteorite of a type not known among present-day meteorite falls and finds. The noble gas data for relict spinels recovered from the meteorite show that it may be a remnant of the body that hit and broke up the L-chondrite parent body, creating one of the major asteroid families in the asteroid belt. After two decades of systematic recovery of fossil meteorites and relict extraterrestrial spinel grains from marine limestone, it appears that the meteorite flux to Earth in the mid-Ordovician was very different from that of today.

5. Conclusions

After two decades of a systematic search for meteorites on the ancient Ordovician seafloor ∼100 ordinary chondrites have been recovered, with all (or almost all) of them being L chondrites (Schmitz, 2013). Here we report on the first recovered meteorite, the “Mysterious Object”, that is not an L-chondrite, but a winonaite-related meteorite of a kind that has no equivalent among the meteorites found on Earth today. Cosmic-ray exposure ages inferred from the relict chrome spinels indicate that the MO is related to the breakup of the L-chondrite parent body. It may be a fragment of (1) the impactor that broke up the L-chondrite parent body, (2) a nearby winonaite-like asteroid hit by a ricochet from the L-chondrite breakup, or (3) a pre-breakup breccia on the L-chondrite parent body. We favor the first alternative because of the rarity of documented winonaite-bearing breccias among recent L chondrites, lack of solar gases and low cosmogenic gas content of MO spinels, and absence of matrix-related L-chondritic spinels in the MO.

If the MO is a piece of the impactor, then the possible role of a winonaite-related object in one of the major, late collisions in the asteroid belt, an event still providing about a quarter of all meteorites to Earth, together with the extreme rarity of winonaite meteorites today, will be challenging to explain in terms of solar system dynamics and meteorite delivery processes. Based on our empirical data it is clear, however, that the meteorite flux to Earth in the mid-Ordovician was very different from that of today.

[KarlW]

Hallo Martin,

mal wieder dankeschön für den aufregenden Hinweis. 

Damit hat unser xenolithischer Einschluss im Villalbeto #33 jetzt ein fossiles Gegenstück.
Nachzulesen in MAPS und PNAS:

Reclassification of Villalbeto de la Pena — Occurrence of a winonaite-related fragment in a hydrothermally metamorphosed polymict L-chondritic breccia
Addi BISCHOFF, Kathryn A. DYL, Marian HORSTMANN, Karen ZIEGLER, Karl WIMMER, and Edward D. YOUNG
Meteoritics & Planetary Science 1–13 (2013)


Early Solar System hydrothermal activity in chondritic asteroids on 1–10-year timescales
Kathryn A. Dyl, Addi Bischoff, Karen Ziegler, Edward D. Young, Karl Wimmer, and Phil A. Bland
http://www.pnas.org/content/109/45/18306

Anders als Schmitz et al. neige ich zur 3. der von den Autoren angeführten Hypothesen. Meinungen dazu würden mich interessieren.

Grüße 
Karl

[karmaka]

Auch hierzu gibt es wieder etwas Neues:

Chromium Isotopes in Ordovician Fossil Meteorites and the Quest for the Impactor that Broke Up the L-Chondrite Parent Body

Schmitz B., Yin Q.-Z., Sanborn M. E., Tassinari M.

78th Annual Meeting of the Meteoritical Society (2015), abstract #5037

LINK

In contrast to  the  chemical  and  oxygen  isotope  data  for  MO  spinels,  that indicate a potential winonaite affinity, the MO has ε54 Cr values  of -0.26 to -0.23, which are within the uncertainties of previously measured ordinary chondrites [4]. The ε54 Cr results for the MO thus rule out a winonaite-like origin as suggested in [2]. The new results  underline  that  the  MO  does  not  resemble  any  known meteorite type.