Tungsten isotope

The ratio of the quadrupole moments in tungsten isotopes as measured by Mossbauer spectroscopy - collected from [222-228] - is... 

Leya I, Wider R, Halliday AN (2000) Cosmic-ray production of tungsten isotopes in lunar samples and meteorites and its implications for Hf-W cosmochemistry. Earth Planet Sci Lett 175 1-12 Loss RD, Lugmair GW (1990) Zinc isotope anomalies in Allende meteorite inclusions. Astrophys J 360 L59-L62... 

Volkening, J., Koppe, M., and Heumann, K. G. (1991) Tungsten isotope ratio determinations by negative thermal ionization mass spectrometry. International Journal of Mass Spectrometry and Ion Processes, 107, 361-368. 

The time scale for Earth s differentiation was discussed in Chapter 9. We learned that tungsten isotopes constrain the time interval between nebula formation and core separation as less than 30 Myr (Yin et al., 2002). Differentiation must have been complete before the giant impact that formed the Moon, currently constrained to have occurred 40—45 Myr after the solar system formed (Halliday, 2004 and references therein). 

Figure 9 Tungsten isotopic compositions for terrestrial standards, meteorites, and lunar samples expressed as deviations in parts/104 from the mean for NIST SRM 3163, as measured by multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). (From Halliday et al., 1998b.)...

Lee, D.-C., and Halliday, A.N. (1998) Tungsten isotopes, the initial 182Hf/180Hf of the solar system and the origin of enstatite chondrites. Mineral. Mag. 62A, 868-869. 

Halliday A. and Lee D. C. (1999) Tungsten isotopes and the early development of the Earth and Moon. Geochim. Cosmochim. Acta 63, 4157-4179. 

CONSTRAINTS FROM LEAD AND TUNGSTEN ISOTOPES ON THE OVERALL TIMING, RATES, AND MECHANISMS OF TERRESTRIAL ACCRETION... 

Introduction Uses and Abuses of Isotopic Models. 4.2 Lead Isotopes. 4.3 Tungsten Isotopes... 

The differences in tungsten isotopic composition are most conveniently expressed as deviations in parts per 10,000, as follows ... 

The tungsten isotopic difference between early metals and the silicate Earth reflects the time integrated HfAV of the material that formed the... 

Earth, relative to average solar system (chondrites). However, the tungsten isotopic difference between early metals and the silicate Earth on its own does not provide constraints on timing. One needs to know the atomic abundance of Hf at the start of the solar system (or the ( Hf/ Hf)Bssn the bulk solar system initial ) and the composition of the chondritic reservoirs from which most metal and silicate reservoirs were segregated. In other words, it is essential to know to what extent the extra in the silicate Earth relative to iron meteorites accumulated in the accreted chondritic precursor materials or proto-Earth with an HfAV 1 prior to core formation, and to what extent it reflects an accelerated change in isotopic composition because of the high HfAV ( 15) in the silicate Earth. 

Both, the uncertainty over ( Hf/ Hf)Bssi and the fact that the tungsten isotopic composition of the silicate Earth is now unequivocally resolvable from a now well-defined chondritic composition (Kleine et al, 2002 Lee and Halliday, 2000a Schoenberg et al., 2002 Yin et al, 2002), affect the calculated timescales for terrestrial accretion. It had been argued that accretion and core formation were fairly protracted and characterized by equilibration between accreting materials and the silicate Earth (Halliday, 2000 Halliday et al,... 

Halliday and I e, 1999). In other words, the tungsten isotope data provide very strong confirmation of the models of Safronov (1954) and Wetherill (1986). This general... 

Figure 9 The tungsten isotopic compositions of lunar samples after calculated corrections for cosmogenic contributions (source Leya et al, 2000).

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