Isotopes Jacobsen

Wasserburg, GJ, Jacobsen SB, DePaolo DJ, McCullock MT, Wen T (198L) Precise determination of Sm/Nd ratios, Sm and Nd isotopic abundances in standard solutions. Geochim Cosmo-chim Acta 45 2311-2323. 

Yin QZ, Jacobsen SB, Yamashita K (2002) Diverse supernova sources of pre-solar material inferred from molybdenum isotopes in meteorites. Nature 415 881-883 Young ED, Galy A, Nagahara H (2001) Kinetic and equilibrium mass-dependent isotope fractionation laws in nature and their geochemical and cosmochemical significance. Geochim Cosmochim Acta 66 1095-1104... 

Jacobsen, S. B. and Wasserburg, G. J. (1980) Sm-Nd isotopic evolution of chondrites. Earth and Planetary Science Letters, 50, 139—155. 

Schafer, T., Buckau, G., Artinger, R., Kim, J. I., Geyer, S., Wolf, M., Bleam, W. F., Wirick, S., and Jacobsen, C. (2005). Origin and mobihty of fulvic acids in the Gorleben aquifer system Implications from isotopic data and carbon/sulfur XANES. Org. Geochem. 36, 567-582. 

The problem with this technique and the reason why it has been so slow to develop is that it is extremely difficult to measure W isotopic compositions by TIMS because of the very high first ionization potential (7.98 eV). Negative ion techniques have met with some success (Volkening et al., 1991 Harper et al., 1991a Harper and Jacobsen, 1996 Jacobsen and Harper, 1996). However, W isotopic compositions can be measured relatively easily by using MC-ICP-MS (Halliday et al., 1995 Lee and Halliday, 1995a,b, 1996, 1997 Lee et al., 1997). 

Jacobsen, S. B., and Harper, C. L., Jr. (1996). Accretion and early differentiation history of the Earth based on extinct radionuclides. In Earth Processes Reading the Isotope Code, A. Basu and S. Hart, eds. Pp. 47-74. American Geophysical Union, Washington D.C. 

E.D. Young, K. Kuramoto, R.A. Marcus, H. Yurimoto, S.B. Jacobsen, Mass-independent oxygen isotope variation in the Solar nebula. Rev. Mineral. Geochem. 68 (2008) 187. 

Tungsten and lead isotopic data can, however, be used to define the timescales for accretion, simply by assuming that core formation, the primary process that fractionates the parent/ daughter ratio, started very early and that the core grew in constant proportion to the Earth (Halliday et al., 1996, 2000 Harper and Jacobsen, 1996b Jacobsen and Harper, 1996 Halliday and Lee, 1999 Halliday, 2000). There is a sound basis for the validity of this assumption, as follows. 

While lead isotopes have been useful, the i 2jjf i82- chronometer (Ti/2 = 9 Myr) has been at least as effective for defining rates of accretion (Halliday, 2000 Halliday and Lee, 1999 Harper and Jacobsen, 1996b Jacobsen and Harper, 1996 Lee and Halliday, 1996, 1997 Yin et al, 2002). Like U-Pb, the Hf-W system has been used more for defining a model age of core formation (Kramers, 1998 Horan et al. 

Nb decays by electron capture to Zr with a half-life of 36 3 Myr. At one time it was thought to offer the potential to obtain an age for the Moon by dating early lunar Umenites and the formation of Umenite-rich layers in the lunar mantle. Others proposed that it provided constraints on the time-scales for the earhest formation of continents on Earth (Miinker et al, 2000). In addition, it was argued that it would date terrestrial core formation (Jacobsen and Yin, 2001). There have been many attempts to utilize this isotopic system over the past few years. To do so, it is necessary to first determine the initial Nb abundance in early solar system objects accurately and various authors have made claims that differ by two orders of magnitude. 

Halliday A. N., Lee D.-C., and Jacobsen S. B. (2000) Tungsten isotopes, the timing of metal-sihcate fractionation and the origin of the Earth and Moon. In Origin of the Earth and Moon (eds. R. M. Canup and K. Righter). University of Arizona Press, Tucson, pp. 45-62. 

As noted above, isotope decouphng between oceanic mantle and crust was observed both in ophiolites (Claesson et al., 1984 Gopel et al., 1984 Jacobsen et al., 1984 Brouxel and Lapierre, 1988 Rampone et al., 1996, 1998) and in abyssal rocks (Snow et al., 1994 Kempton and Stephens, 1997 Salters and Dick, 2002). In most examples, the mantle rocks are distinguished from the oceanic crust by more depleted isotopic compositions, generally reflected by higher Nd/ Nd values. However, the interpretations proposed for the ophiolites and for the abyssal peridotites are markedly different. 

Jacobsen S. B., Quick J. E., and Wasserburg G. J. (1984) A Nd and Sr isotopic study of the Trinity Peridotite imphcations for mantle evolution. Earth Planet Sci. Lett. 68, 361-378. 

Lee C. T., Yin Q., Rudnick R. L., Chesley J. T., and Jacobsen S. B. (2000a) Osmium isotopic evidence for Mesozoic removal of lithospheric mantle beneath the Sierra Nevada. Science 2S9, 1912-1916. 

Jacobsen S. B. (1988) Isotopic constraints on crustal growth and recycling. Earth Planet. Sci. Lett. 90, 315-329. 

Kellogg J. B., Jacobsen S. B., and O Connell R. J. (2002) Modeling the distribution of isotopic ratios in geochemical reservoirs. Earth Plan. Sci. Lett. 204, 183 -202. 

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