Combined U-Pb and Lu-Hf isotope analyses by laser ablation MC-ICP-MS: methodology and applications
Lu-Hf method. The high Lu/Hf ratios found in garnets make these minerals useful for Lu–Hf dating of metamorphic events. Eclogites from three units of the. Lutetium-hafnium ages that are based on the previously used λLu of highly enriched in the parent elements for both Lu-Hf and U-Pb dating methods. PDF | DefinitionThe radiogenic isotope applications of the Lu-Hf system utilize Lutetium is the heaviest of the rare-earth elements (REEs) and.
Standard Solutions Analyses In terms of signal stability, the ICP-MS solution system solution sample has more accuracy than laser ablation analyses; so, before starting the laser ablation sessions, we routinely calibrate the spectrometer with solutions.
For this reason, the first objective in the development of this systematic has been to prepare a Hf standard solution. Then, we prepared a ppm stock solution and, starting from this, a 1 ppm sub-stock solution and a ppb solution for analyses have been produced. In Figure 1 a typical result for a cycles analysis of JMC standard solution is shown.
As explained before, the measurement of Lu-Hfisotopes on zircons is made on a crystal previously analyzed by laser ablation U-Pb method to obtain age information. Spatially, the two spot analyses have to be as close as possible in order to analyze portions of the zircon grain with the same isotopic characteristics.
Before the in situ analysis, we should obtain as more information as possible about the structure of the zircon, such as zoning composition, growth pattern and presence of inherited core. It should prevent to analyses of portions of the zircon with different Hf and Pb isotopic compositions that would generate misleading results. The best methods to obtain images of the internal structure of zircon on polished surfaces are the Cathodoluminescence CL and the Back-Scattered Electrons BSE techniques.
For the Lu-Hf method, the BSE imagery is preferable because the brightness of the image is atomic mass dependent and, for that, it is possible to easily discriminate regions with different Hf content in the same zircon crystal.
Higher brightness in the image corresponds to higher Hf contents in the zircon Hanchar and MillerCorfu et al. As the raster ablation does not consume much material and produce a low deep hole on the zircon surface, in some case it is possible to do the Lu-Hf analyses in the same local of the previous U-Pb analyses.
For Lu-Hf method, we chose a laser configuration following the most recent literature Gerdes and Zeh To improve the stability of the signal, we chose a low laser frequency of about Hz. The power of the laser used during the analytical session depends mainly on the Hf contents of the analyzed zircons, especially the standard one.
The Helium flux has to be calibrated together with the Sample gas or Spare gaswhich aids the sample to entry the plasma, and, so, obtaining the higher and more stable signal. For an example of geological application, two complex zircons from a paleoproterozoic migmatite from the Borborema Province were analyzed. The U-Pb raw data are translated to an Excel spreadsheet for data reduction and, when necessary, we corrected the laser induced mass bias using the method of Kosler et al.
Lu-Hf The acquired Lu and Hf isotope data are corrected online for mass bias fractionation and isobaric interferences. The signals of the interference-free isotopes Yb, Yb and Lu are onitored during the analyses in order to remove isobaric interferences of Yb and Lu on Hf signal Table I. The Yb and Lu contribution are calculated using the isotopic abundance of Lu and Hf proposed by Chu et al.
For solution analyses, 4 blocks of 40 cycles and an integration time of 4 seconds are employed. The obtained results are listed in Table II. Before the analytical session, the MADA zircon has been previously studied with the BSE technique in order to evaluate a possible growth zoning. The BSE image obtained for the analyzed grain shows that it is very homogeneous in terms of Hf content, do not showing any internal structures. The studied zircons have been separated from a leucocratic portion of migmatitic rock from the Rio Grande do Norte terrain in the Borborema Province.
Images of the selected zircons in backscattered electrons BSE mode were obtained using a Scanning Electron Microprobe SEM in order to have information on the internal structure of the studied zircons.
The BSE images permitted us to differentiate Hf-rich and Hf-poor portions of zircons, characterized by high and low brightness response, respectively. The studied zircons show a typical flat shaped meta-morphic morphology and complex internal structures Fig.
Every portion of each zircon grains showing peculiar and distinctive characteristics based on the interpretation of BSE images has been analyzed. Initial Hf composition for each zircon has been calculated using the U-Pb age of the correspondent spot.
In Figure 4 the Concordia diagrams for the obtained data on two zircons are shown. The two analyses of zircon 1 Fig. The U-Pb analyses on zircon 12 also define Fig. In Figure 4c a graphic interpretation of the slightly discordant rim data for zircon 12 is shown. The distribution of these younger analyses may be interpreted in two different ways: In this case, as shown in Figure 4cit is possible that the laser accidentally ablated a portion ofthe older core.
Hafnium | Revolvy
The total signal of such analysis, representing a mixing of two different portions of the zircons, would be plotted on a discordia line defined by the two different end-members U-Pb isotopic compositions. The TDM Hf model ages for the Paleoproterozoic cores of the two analyzed zircons are similar, ranging between 2.
These magmas may have been formed by partial melting of an older juvenile crust generated at 2. The Hf isotopic composition of Neoproterozic rims suggests that they could not crystallized in magma derived by partial melting of a 2. This process would have reset almost entirely the U-Pb system, leaving unaltered the Hf isotopic composition. The Hf isotopic compositions for three zircon standards have been measured. The Lu-Hf isotopic composition for the zircon standard UQ-Z and for a in-house zircon standard is reported.
New U-Pb and Lu-Hf isotopic data were obtained for two zircons selected from a migmatitic rock from the Borborema Province. The U-Pb, Lu Hf in situ analyses, combined with BSE imaging, permitted to study in detail the internal isotopic composition of the zircons and to obtain information about the growing history of each zircon.
This work is part of the postdoctoral research of the first author. The Lu-Hf isotope geochemistry of chondrites and the evolution of the mantle-crust system. Earth Planet Sci Lett An Acad Bras Cienc A hafnium isotope and trace element perspective on melting of the depleted mantle.
Earth Planet Sc Lett Pb diffusion in zircon. Rare earths diffusion in zircon. Hf isotope ratio analysis using multi-collector inductively coupled plasma mass spectrometry: J Anal Atom Spectrom Atlas of zircon textures. Trace element and isotopic composition of GJ-red zircon standard by laser ablation. Goldschmidt Conference abstracts, A The Hf isotope composition of cratonic mantle: Geochim Cosmochim Ac Hafnium's large neutron capture cross-section makes it a good material for neutron absorption in control rods in nuclear power plantsbut at the same time requires that it be removed from the neutron-transparent corrosion-resistant zirconium alloys used in nuclear reactors.
Characteristics Physical characteristics Pieces of hafnium Hafnium is a shiny, silvery, ductile metal that is corrosion -resistant and chemically similar to zirconium due to its having the same number of valence electronsbeing in the same group, but also to relativistic effects ; the expected expansion of atomic radii from period 5 to 6 is almost exactly cancelled out by the lanthanide contraction.
The physical properties of hafnium metal samples are markedly affected by zirconium impurities, especially the nuclear properties, as these two elements are among the most difficult to separate because of their chemical similarity. The most notable nuclear properties of hafnium are its high thermal neutron-capture cross-section and that the nuclei of several different hafnium isotopes readily absorb two or more neutrons apiece. Chemical characteristics Hafnium dioxide Hafnium reacts in air to form a protective film that inhibits further corrosion.
The metal is not readily attacked by acids but can be oxidized with halogens or it can be burnt in air. Like its sister metal zirconium, finely divided hafnium can ignite spontaneously in air. The metal is resistant to concentrated alkalis. The chemistry of hafnium and zirconium is so similar that the two cannot be separated on the basis of differing chemical reactions. The melting points and boiling points of the compounds and the solubility in solvents are the major differences in the chemistry of these twin elements.
A potential source of hafnium is trachyte tuffs containing rare zircon-hafnium silicates eudialyte or armstrongite, at Dubbo in New South WalesAustralia. Production Melted tip of a hafnium consumable electrode used in an electron beam remelting furnacea 1 cm cube, and an oxidized hafnium electron beam-remelted ingot left to right The heavy mineral sands ore deposits of the titanium ores ilmenite and rutile yield most of the mined zirconium, and therefore also most of the hafnium.keva product book
However, because of hafnium's neutron-absorbing properties, hafnium impurities in zirconium would cause it to be far less useful for nuclear-reactor applications. Thus, a nearly complete separation of zirconium and hafnium is necessary for their use in nuclear power.
The production of hafnium-free zirconium is the main source for hafnium. The chemical properties of hafnium and zirconium are nearly identical, which makes the two difficult to separate.
After zirconium was chosen as material for nuclear reactor programs in the s, a separation method had to be developed. Liquid-liquid extraction processes with a wide variety of solvents were developed and are still used for the production of hafnium. The end product of the separation is hafnium IV chloride.
The hafnium forms a solid coating at the tungsten filament, and the iodine can react with additional hafnium, resulting in a steady turn over. Halogens react with it to form hafnium tetrahalides. They are volatile solids with polymeric structures. At the time of his formulation inMendeleev believed that the elements were ordered by their atomic masses and placed lanthanum element 57 in the spot below zirconium.
The exact placement of the elements and the location of missing elements was done by determining the specific weight of the elements and comparing the chemical and physical properties.