Other
Scientific paper
Sep 1970
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1970phdt........72p&link_type=abstract
Thesis (Ph.D.) -- California Institute of Technology, 1970. Advisor(s): Wasserburg, Gerald J.
Other
1
Basaltic Achondrites, Initial 87Sr/86Sr Chronometer, Meteorite Chronology, Solar System Chronology
Scientific paper
A new solid source single focusing, sector magnet mass spectrometer was developed with a programmable magnetic field analyzer of stability [...]. Digital data are obtained during a completely automatic sequence and include the real time at which an intensity measurement is made. An on line computer analyses the data and returns the results to the operator throughout a run. The precision obtained in measuring isotopic ratios is increased by an order of magnitude over conventional similar instruments and is documented for the strontium isotopes. The [...] ratio is measured to better than [...] 0.007% over the extended time of the experiments.Ca-rich achondritic meteorites having a total spread of 0.2% in [...] were studied and appear to define an identical initial abundance of 0.698983 [...] 0.000032. The samples lie on a well defined isochron with slope 0.0642 [...] 0.0034, corresponding to an age of 4.47 [...] 0.24 x [...] years. The maximum deviation of data points from the isochron is 6 x [...] and shows that these samples were formed over a time interval of 1.6 x [...] years if they were derived from an environment of solar Rb/Sr abundance. The Angra dos Reis achondrite has the distinctly lower inital Sr composition of 0.69884 [...] 0.00004 and is, therefore, derived from more primitive material than any other meteorite measured. Angra dos Reis may have formed 5.4 x [...] years earlier than the other achondrites (from a solar Rb/Sr environment). The Angra dos Reis initial Sr isotopic composition should be considered as the best estimate of the primordial Sr isotopic abundance in the solar system.Measurements on the chondrite Guarena yield an age 4.56 [...] 0.08 x [...] years and precise Sr initial composition of 0.69995 [...] 0.00015. This is evidence for either a late formation of Guarena or a metamorphic event taking place 74 x [...] years after the time of formation of the Ca-rich achondrites. These measurements may yield a time index for the classification of meteorites.Measurements on Apollo XI lunar samples are presented and discussed.
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