ISSN:
1572-946X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Physics
Notes:
Abstract The type I carbonaceous chondrites, with volatiles between 24 and 30% (at 1000 C, N2 atm.), contain the maximum percentage of the low-temperature ground mass, in which the high-temperature minerals are dispersed as ‘microchondrules’. In the type II carbonaceous chondrites (vol. 12–24%), the loosely cohering aggregates of microchondrules, ‘grape-bunch chondrules’, reach a maximum. The type III carbonaceous chondrites and some enstatite chondrites (vol. 2–12%) contain the maximum of the ‘partly coalesced chondrules’, in which microchondrules of olivine and nickel-iron appear. The ureilites are interpreted as impact shocked aggregates of microchondrules in differing states of coalescence. The ‘fully coalesced chondrules’ are characteristic for the ordinary chondrites with volatiles below 1%. It appears that the evolution of chondrules with the decrease of volatiles in meteorites subdivides into: (A) primary condensation of microchondrules with diameters of 0.01 mm; (B) secondary accretion of the former into the chondrules of diameter range ±1 mm. The observations may be explained through the hypothesis that at the highest-temperature stage of condensation of the asteroid-type parent body was an incandescent cloud (preserved through the solidification of chondrules at an early stage of degassing) covered with cosmic dust. The carbonaceous chondrites orginate from the marginal incandescent fog and the correspondingly deeper zones of the incandescent cloud mantle. The absence of typical chondritic rocks on earth may be explained by the slower cooling rate of this celestial body of relatively greater mass.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00651261
