[meteorite-list] Age of chondrites and achondrites

[bernd.pauli at paulinet.de]

Pierre-Marie wrote:

"A recent study on angrite Sahara 99555 concluded to the fact that this achondrite
was the oldest stone ever analyzed ... Can you explain me why this achondrite (and
maybe others) were formed before primitive chondrites ?"

Hello All,

Some scientists believe that angrites formed by differentiation of very CAI-rich material
and CAIs predate the formation of primitive chondrites. CAIs, some scientists say, predate
the beginning of chondrule formation by at least 1.3 Myr. Angrites crystallized very early
in the solar system's history and may have been subjected to a short but very intense period
of heating.

References:

WARREN P.H. et al. (1995) Angrites: A volatile-rich variety of asteroidal
basalt - except for alkalis and gallium! (abs. Meteoritics 30-5, 1995, 593.

HUTCHISON R. (2004) Meteorites: A Petrologic, Chemical, and Isotopic
Synthesis (Cambridge Planetary Science Series, pp. 506, p. 172).

=> See also David Weir's website and click on Sah 99555 ! <=


Cheers, Salut,

Bernd