HR: 0800h
AN: P51A-0899    [Abstracts]
TI: U-Pb Isotope Systematic of SNC Meteorites
AU: * Jagoutz, E
EM: jagoutz@mpch-mainz.mpg.de
AF: Max Planck Institut, Saarstrasse 23, Mainz, 55121 Germany
AU: Jotter, R
EM: jotter@mpch-mainz.mpg.de
AF: Max Planck Institut, Saarstrasse 23, Mainz, 55121 Germany
AU: Kubny, A
EM: kubny@mpch-mainz.mpg.de
AF: Max Planck Institut, Saarstrasse 23, Mainz, 55121 Germany
AU: Zartman, R
EM: zartman@mpch-mainz.mpg.de
AF: Max Planck Institut, Saarstrasse 23, Mainz, 55121 Germany
AB: A stepwise dissolution technique was applied to several nakhlite meteorites that were heavily contaminated by terrestrial Pb. Pulverized samples were subjected to three acid leaches of increasing strength followed by HF-HNO3 digestion of the remaining residue. Using this procedure the major portion of the terrestrial contamination was removed in Leaches 1 and 2, while essentially uncontaminated Pb was recovered in Leach 3 and the Residue. We give further details here about some of the insights gained from this improved ability to distinguish between the primary and terrestrial Pb components in meteorites. Firstly, we ran one sample of Nakhla as a test of the procedure. The result showed L1 and L2 to be mainly dominated by terrestrial Pb while L3 yielded Pb close to the initial Pb of other Nakhlites. The Pb in the Res, however, was very radiogenic and had a 206Pb/204Pb relative to 207Pb/204Pb indicating a drastic increase of the U/Pb at 1.3 Ga. Furthermore, the relatively unradiogenic 208Pb/204Pb suggested that there might be zircon or other high U/Th mineral in the Res. We made an in-depth study on a thin-section using an electron microscope and found indeed tiny 10 �m grains of Baddeleyeite. The same dissolution technique was then applied to other Nakhlites from the Antarctic NIPR collection and NASA (MIL) with similar results, indicating that all Nakhlites may have the same age. In addition, an identical initial Pb isotopic composition indicates that all of these meteorites were derived from the same homogeneous source. Moreover, it is strongly suggested by their initial Pb that the "olivine Shergottites", like SAU, DAG, Que, and Y, likewise come from this Nakhla source. While "normal" Shergottites like Shergotty, LA are from sources having a more evolved Pb isotopic composition. "Olivine Shergottites" are clearly younger than Nakhlites. Their Sm Nd and Rb Sr isotopic systems are highly disturbed. Analyzing the existing data we favor an age of 800 my for the "olivine Shergottites" which is also suggested by Ar-Ar systematic. The Nakhla reservoir were sampled at least 2 times: at 1300my (Nakhlites) and at 800 my (olivine Shergottites). However, the Pb isotopic composition plot close to the Geochrone at a 238U/204Pb of about 2. This gives interesting implications for the evolution of this reservoir and their parent body.
DE: 1040 Radiogenic isotope geochemistry
DE: 1160 Planetary and lunar geochronology
DE: 5220 Hydrothermal systems and weathering on other planets
DE: 6063 Volcanism (5480, 8450)
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: Fall Meeting 2005