Origin and Evolution of Condrules Based on Na/Al-Dispersion and -Convergence in Yamato-74 Ordinary Chondrites

Abstract

Na/Al convergence has been observed in groundmass of chondrules and matrix from seven Yamato-74 (H, L, 4-5) chondrites. On the other hand, Na/Al dispersion has prevailed in groundmass of chondrules and matrix from Yamato-74191 (L3) chondrite. The results suggest that : (1) Primordial liquid droplets as precursors of the chondrules might be derived from a rapidly cooling solar nebula by fractional condensation. (2) The hot liquid droplets thus formed might be cooled instantaneously by radiation loss in the cooling nebula. (3) The chondrules as quenched products might be subjected to mutual collision during accumulation in the cold nebula. (4) Planetesimals accumulated by the chondrules might be transferred from the place of birth to an unknown hot region in the proto solar nebula