Hf isotopes

Blichert-Toft J, Alberede F (1997) The Lu-Hf isotope geochemistry of chondrites and the evolution of the mantle-crast system. Earth Planet Sci Lett 148 243-258... 

Patchett J. P. (1983). Importance of the Lu-Hf isotopic system in studies of planetary chronology and chemical evolution. Geochim. Cosmochim. Acta, 47 81-91. 

Sr-Nd-Pb-Hf isotope ratios display comparable range of values in the silicic and mafic rocks and are closer to crustal than to mantle compositions (Fig. 2.4 Vollmer 1976 Hawkesworth and Vollmer 1979 Conticelli et al. 2002 Gasperini et al. 2002 author s unpublished data). These crustal-like isotopic signatures have led early authors to suggest a crustal... 

Hf-isotope ratios also fall close or within the field of crustal rocks (Fig. 2.4 Table 2.2). This has been interpreted as evidence that metasomatic modification of lamproitic mantle sources in Tuscany was provided by addition of crustal material (e.g. metapelites). Interestingly, the mantle-normalised incompatible element patterns of Tuscany lamproites are similar to those of gneisses and schists in almost eveiy detail. This has been interpreted as evidence for addition of bulk upper crustal material to the mantle, with little element fractionation during metasomatism and the subsequent partial melting (Peccerillo 2002). This makes the Tuscany Province a zone where the upper mantle magmas look very much like the upper crust in terms of trace element and radiogenic isotope compositions. 

In the Rf experiments [35] performed at the PSI Philips Cyclotron, 261Rf was produced in the Cm O, 5n) reaction at 100 MeV. The target contained 10% Gd enriched in 152 Gd to produce simultaneously short-lived Hf isotopes that were used to monitor the behavior of Hf and to perform yield checks by Y spectroscopy. Rf and Hf were transported by a He(KCl) gas jet and were collected for 90s by impaction inside ARCA II [7]. The deposit was dissolved in 200 pL 0.1 M HNO3/X M HF (x variable) and was fed onto the 1.6x8 mm cation-exchange column at a flow rate of 1 mL min 1. The effluent was evaporated to dryness as sample 1. In order to elute remaining Rf and Hf from the column, a second fraction of 200 pL 0.1 M HNO3/O.I M HF was collected to strip all group-4 elements from the column. The fraction was prepared as sample 2. 

In 2005, De Laeter discussed the role of isotope reference materials for the analysis of non-traditionaT stable isotopes. At present, no isotopically certified reference materials exist for a large number of elements, including Cu, Zn, Mo and Cd, and it is important that this situation be rectified as soon as practicable. Before the isotopically certified reference materials become available for selected elements, suitable reference materials can be created as a standard if sufficient and reliable isotope data have been obtained by interlaboratory comparisons. For example, the Hf/ Hf isotope ratio was measured using hafnium oxide from Johnson Matthey Chemicals, JMC-475, for hafnium isotope ratio measurements with different multi-collector mass spectrometers (ICP-MS and TIMS) as summarized in Table 8.1. However, no isotope SRM is certified for the element Mo either. Mo isotope analysis is relevant, for example, for studying the isotope fractionation of molybdenum during chemical processes or the isotope variation of molybdenum in nature as the result of the predicted double (3 decay of Zr or 18.26-28 spectroscopically pure sample from Johnson Mattey Specpure is proposed as a laboratory standard reference material if sufficient and reliable isotope data are collected via an interlaboratory comparison. 

Precise and accurate measurements of nltralow Nb, Ta, Zr and Hf concentrations and the chondritic Zr/Hf and Nb/Ta ratios by MC-ICP-MS (Isoprobe, Micromass) were examined by Weyer et al. For the development of the isotope dilution techniqne, enriched °Ta, Zr and °Hf isotopes were apphed for quantitative Zr, Ta and Hf determination, and the monoisotopic element Nb was measnred relative to Zr after quantitative separation from the matrix by ion exchange. 

It has been recognized that the Lu-Hf isotopic system in zircon is a powerful tool for deciphering the evolution of the earth s crust and mantle. " Zircon normally contains 0.5-2 wt % Hf, which results in an extremely low Lu/Hf ratio (" Lu/" Hf < 0.002) and consequently a negligible radiogenic growth of Hf due to the decay of Lu. Therefore, the Hf/" Hf ratio of zircon can be regarded as the initial value at the time when it crystaUized. LA-ICP-MS with a multiple ion collector system has also been employed to study the hafnium isotopic composition of zircon and baddeleyite standards in U-Pb geochronology. °°... 

The time of core formation on the Earth and Mars can be constrained using chronometers based on short-lived isotopes. The W-Hf isotope system is particularly useful in this respect, consisting of a lithophile parent nucleus, which decays to a siderophile daughter isotope with a half-life of 9 Myr. Recent measurements of an excess of the daughter isotope indicate that the cores of Mars and Earth formed in less than 13 Myr and 30 Myr, respectively (Kleine et al., 2002 Yin et al., 2002 see Chapter 1.20 by Halliday for a more detailed discussion). 

Bandermann L. W. and Singer S. F. (1973) Calculation of meteoroid impacts on Moon and Earth. Icarus 19, 108-113. Beard B. L., Taylor L. A., Scherer E. E., Johnson C. M., and Snyder G. A. (1998) The source region and melting mineralogy of high-titanium and low-titanium lunar basalts deduced from Lu-Hf isotope data. Geochim. Cosmochim. Acta 62, 525-544. 

Blichert-Toft J., Frey F. A., and Albarede F. (1999) Hf isotope evidence for pelagic sediments in the source of Hawaiian basalts. Science 285, 879-882. 

Kempton P. D., Pearce J. A., Barry T. L., Fitton J. G., Langmuir C. H., and Christie D. M. (2002) Sr-Nd-Pb-Hf isotope results from ODP Leg 187 evidence for mantle dynamics of the Australian-Antarctic Discordance and origin of the Indian MORE source. Geochem. Geophys. Geosys. 3, 10.29/ 2002GC000320. 

Blichert-Toft J., Albarede F., and Kornprobst J. (1999) Lu-Hf isotope systematics of garnet pyroxenites from Beni Bousera, Morocco implications for basalt origin. Science 283, 1303-1306. 

There are few pubhshed Lu-Hf isotope studies of mantle xenohths because of difficulties in efficient ionization of hafnium by thermal ionization mass spectrometers. Multicollector plasma mass spectrometers are a solution to this problem and data are emerging that promise to be a more revealing tool in mantle environments than neodymium isotopes. The variety of Lu/Hf fractionation displayed by mantle minerals (Figure 42) indicates that, as with other isotope systems, isotopic variation should be considerable and initial results are confirming this. Salters and Zindler (1995) found very radiogenic Hf/ Hf at relatively unradiogenic neodymium isotope compositions in spinel peridotites from Salt Lake Crater, Hawaii. Radiogenic Hf/ Hf also characterizes low-T circum-cratonic... 

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