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Isotopic Lead Investigations on Bo County Chondrite of Anhui Province, China

Peng Zi-cheng   

  1. Dept. of Earth and Space Science, University of Science and Technology of China
  • Received:1985-01-19 Revised:1900-01-01 Online:1986-08-24 Published:1986-08-24

Abstract: The isotopic compositions of lead were determined on the samples of whole rock, chondrule, olivine, pyroxene and troilite from Bo County chondrite (class LL4) of Anhui prov., China. Uraium, Thorium, and Lead concentrations of those samples were partially analysed. Observed 206Pb/204Pb ratios varied from 9.87 to 20.38; 207Pb/204Pb ratios from 10.51 to 16.61; 208Pb/204 Pb ratios from 30.20 to 40.58. In 207Pb/204Pb-206 Pb/204Pb diagram, a regression line fitted to most of data from Bo County and Bru-derheim-III and Modoc meteorites, has a slope of 0.6095 + 0.0095, corresponding to the model age of 4.53 ± 0.02 AB and the line is through the primordial lead of Canyon Diablo troilite. However, the age, corresponding to the internal isbehron line of Bo County chondrite, is 44.4±0.02 AE. It is reasonable to think that Bo County chondrite was formed at 4.53±0.02 AE ago and suffered in the early melting event at about 0.1 AE ago after formed. In a coreordia diagram the data plot a chord intersecting concordia at 4.54±0.02 AE and 0.4 AE. This indicates disturbance of the U-Pb systems happened relatively recently. The Th/U ratio from the 208Pb/204Pb- 206Pb/204 Pb diagram of the Bo County samples is 4.0 + 0.1, which is slightly higher than the normal value of 3.8. It is possible that Bo County chondrite might have suffered a thermal event.

Key words: Near-Earth magnetotail, Convective high-speed flow, Near-Earth plasma sheet, Substorm onset