Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p52b0578j&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P52B-0578
Physics
1040 Isotopic Composition/Chemistry, 3662 Meteorites, 5455 Origin And Evolution, 6225 Mars
Scientific paper
In the last years several new meteorites have been found which belong to the SNC family. SNC meteorites are the only available samples we currently have from Mars, therefore their properties are very important to study the formation and evolution of this planet. To get more inside in the petrogenesis of the SNCs we try to measure their initial Pb isotopic compositions. SaU 005 and DaG 476 are among the most recent finds (deserts of Oman and Libya, respectively). Together with Los Angeles (desert of California) they belong to the basaltic shergottites. SaU, DaG, and LA were affected for long time by terrestrial alteration in the deserts, instantaneously after their fall, however with different degree. Therefore, terrestrial lead had strongly influenced their isotopic systems and it is difficult to obtain reliable initial lead data without terrestrial contamination. We tried to get initial lead isotopic values following two different strategies. Firstly, we used a multi-step leaching procedure. Finely powdered whole rock samples were leached stepwise with three different acid solutions of increasing strength. The remaining residues were dissolved in a mixture of HF and HNO3. Secondly, we directly separated very small grains of plagioclases from SaU, DaG, and LA. Feldspars are known to yield reliable initial Pb compositions because their Pb ratios remained unchanged for long periods of time and preserve a record of the initially incorporated lead. For our refined mass spectrometric technique we only needed a few milligrams of sample. The grains were further purified by leaching with HCl/HNO3 (3:1) and diluted HF in an ultra sonic bath. With our refined chemical anion exchange procedure we were able to yield Pb, U, and Th from the dissolved samples in concentrations which allowed us to measure the isotopic ratios at a very low Pb blank level of ~2 pg. Here, we want to report experimental details of our work. The results of our whole rock leaching experiments together with the initial Pb isotopes of clean plagioclase separates will be presented and discussed in a 207Pb/204Pb vs. 206Pb/204Pb diagram.
Jagoutz Emil
Jotter R.
Zartman R.
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