HR: 08:00h
AN: V21F-01    [Abstracts]
TI: Barium and Neodymium Isotope Heterogeneities in Early Solar System Materials: Applications to Planetary Reservoir Models
AU: * Ranen, M C
EM: ranen@fas.harvard.edu
AF: Harvard University Department of Earth and Planetary Sciences, 20 Oxford St, Cambridge, MA 02138 United States
AU: Jacobsen, S B
EM: jacobsen@neodymium.harvard.edu
AF: Harvard University Department of Earth and Planetary Sciences, 20 Oxford St, Cambridge, MA 02138 United States
AB: Heavy element isotopic heterogeneities in early Solar System materials may exist as a result of both incomplete mixing of pre-solar nucleosynthetic components in the Solar Nebula leading to different ratios of p-, r- and s-process isotopes in bulk planetary materials as well as heterogeneities caused by the decay of now extinct nuclides. Boyet and Carlson (2005) reported a difference in ¹⁴²Nd/¹⁴⁴Nd between Earths mantle and chondrites of about 20-30 ppm. Assuming that this difference was due to decay of ¹⁴⁶Sm and that the Earth and chondrites formed with identical ¹⁴⁶Sm/¹⁴⁴Sm they inferred the formation of a deep enriched silicate layer (D'' ?) in the Earth that formed within the first 30 Myr of Solar System history. We have obtained a similar difference in ¹⁴²Nd/¹⁴⁴Nd between Earth and chondrites. However, we are now testing their interpretation with Ba isotope measurements of various chondrites. Barium is an ideal element for testing the origin of small isotopic anomalies because it has two isotopes (134 and 136) derived only from the s-process as well as three isotopes (135,137 and 138) derived from both the r- and s-process with ¹³⁵Ba possibly having a contribution from the decay of now extinct ¹³⁵Cs. Six chondrites: Allende (CV3), Peace River (L6), Murchison (CM2), Grady (H3.7), Guarena (H6), and Bruderheim (L6) were measured for Ba isotopic composition with a new generation TIMS instrument (a GV ISOPROBE-T). A terrestrial andesite, AGV-1, was also processed for use as our reference standard. Preliminary results indicate widespread heterogeneity in the fractionation corrected ¹³⁷Ba/¹³⁶Ba ratio between different meteorites and our terrestrial standard, as high as 25 ppm. Smaller anomalies are also seen in ¹³⁴Ba/¹³⁶Ba. These anomalies are likely caused by slight differences in the mixing proportions of r- and s-process Ba in Earth and chondrites. This calls into question whether or not the differences seen in ¹⁴²Nd/¹⁴⁴Nd are truly caused by early differentiation of the Earth and decay from ¹⁴⁶Sm or are they the result of incomplete mixing of r and s components in the solar nebula.
DE: 1000 GEOCHEMISTRY
DE: 1027 Composition of the planets
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
DE: 6200 PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS
DE: 6240 Meteorites and tektites (1028, 3662)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005