Other
Scientific paper
Jun 1973
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1973gecoa..37.1603l&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 37, Issue 6, pp.1603-1623
Other
15
Scientific paper
The fractional condensation of Bi, Cd, In, Pb and Tl from a cooling gas of cosmic composition is calculated. Predicted absolute and relative abundances of the elements are in good to excellent agreement with the analytical data. This strongly suggests that the presently observed abundances were established at the time of accretion. There is no need to invoke non-equilibrium during condensation or element redistribution after accretion to explain the observations. The elements may therefore be used as cosmothermometers to predict accretion temperatures. Calculated accretion temperatures fall in the range of 420 to 540°K. But a large percentage of each chrondrite group (H, L, LL and E) fall within much narrower intervals, 20° K . This implies that the bulk of each group accreted over a narrow temperature range which is consistent with their uniform oxidation states and O 18 / O 16 ratios. In fact, temperatures inferred from the oxidation state and oxygen isotopes are in excellent agreement with the trace element data. The condensation curves of all these elements are pressure-dependent but are confined to fall in the temperature interval 400 to 600°K owing to the absence of Fe 3 O 4 and the presence of FeS in ordinary chrondrites. Absolute upper and lower limits on the total pressure can thus be deduced: 10 -3 to 10 -6 atm. In addition, the condensation curves for Bi and In cross over at T = 462° K and P t = 2 × 10 -5 atm. The observed relative abundances of Bi and In suggest the L-group formed at slightly lower and the H-group at slightly higher P and T .
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