A robust method is described allowing the sequential separation of Hf and the lanthanides from matrix elements of silicate rocks or minerals. This is based on a single chromatographic column filled with the conventional cation-exchange DowexAG50W-X8 resin, and hydrochloric, nitric and sulfuric acids as eluting agents. The precision and accuracy of the method were evaluated by repeat analyses of four geological Reference Materials covering a range of silicate rock compositions. Already have an account? Login in here. Journal home Journal issue About the journal. A straightforward separation scheme for the concomitant isolation of Lu, Hf, Sm, and Nd prior to isotope ratio and isotope dilution measurements following sample decomposition by Lithium metaborate fusion or Hydrofluoric acid dissolution. Keywords: chromatography , Lu-Hf , Sm-Nd , isotope dilution-mass spectrometry , silicates. Article overview.
The Lu–Hf dating of garnets and the ages of the Alpine high-pressure metamorphism
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My research interests focuses on crust forming processes in the Archaean aeon, and on igneous and metamorphic processes in orogens. I work with petrography, geochemistry, isotope geochemistry and geochronology mainly zircon geochronology. My current research is focused on south east Greenland on the Skjoldungen and Ammassalik regions. In the Skjoldungen region my studies are focused on basement gneisses and granites that formed during a major geological event some 2.
In the Ammassalik region I focus on the chronology of thrust sheets, related to the ca 1. My main interest, in the field of LA-ICP-MS analyses see lab homepage , is focused on developing trace element mapping methods and on refining methods for U-Pb isotope age dating and combining U-Pb age dating with trace element analyses. Retrieved from Lund University’s publications database. Alexandre de Oliveira Chaves, Richard E. Tomas Naeraa, A.
Providing customized analytical solutions at the highest standards of quality assurance and quality control. Samples for U-Pb dating are processed using a Rhino jaw crusher, a Bico disk grinder equipped with ceramic grinding plates, and a Wilfley wet shaker table equipped with a machined Plexiglass top, followed by conventional heavy liquid and magnetic separation using a Frantz magnetic separator. Four binocular microscope workstations are available for sample picking.
The external morphology of mineral grains for analysis can be documented by SEM, and internal structure can be examined in polished grain mounts by cathodoluminescence imaging.
The Lu-Hf method has been used in the investigation of geological samples in elements with the consequent dating routine in several isotopic laboratories in.
The Lu-Hf isotope system, with applications to geo- and cosmochemistry, was first investigated in the early s Patchett b ; Patchett and Tatsumoto a, b , c , following the successful implementation of the Rb-Sr and Sm-Nd isotope systems several years earlier. There are some obvious similarities between the Lu-Hf and Sm-Nd isotope systems and, as a result, they have long been used in concert in a wide range of studies e. In these two systems all elements are lithophile and refractory with high condensation temperatures.
Because of these characteristics it has long been assumed that their abundances in the Earth can be approximated by chondritic meteorites see discussion below. In addition, all elements in these systems behave incompatibly during melting and are concentrated in the melt over the residual solid. In both systems, the daughter element e.
Both Lu and Hf are highly immobile and insoluble and, as is the case with the Sm-Nd system, are thought to be resistant to perturbations and retain their isotopic information through significant degrees of alteration and metamorphism. These differences can confer some advantages to the Lu-Hf isotope system for both geochronology and tracer isotopic work as will be discussed below.
There are a few phases, however, with high affinity for Lu, which make them highly useful in geochronology in both magmatic e. In addition, some other phases particularly phases with Zr or Ti as stoichiometric constituents have strong affinities for Hf e. Although the Lu-Hf system was introduced to the geochemical and cosmochemical communities in the s, analytical challenges limited the widespread use of this technique until the late s.
The reason for this is that Hf has a very high first ionization potential 6.
Hf-w dating Iowa
Our primary goals are as follows:. As described in our Covid video , we have been operating with only lab employees no visitors working on high-priority samples. We are now allowed to have external researchers conduct analyses in our labs, so long as stringent guidelines are followed. Check out and complete our Re-Entry Form if interested.
If you prefer to not travel, we are able to perform the analyses needed for your project, and you will be able to w atch and participate in lab activities through live Zoom or TeamViewer sessions. Please contact Mark Pecha mpecha email.
Because of the low concentrations of Lu and Hf and the very long half-life of Lu 35, million years , the accurate use of the Lu-Hf method has been limited until recent technological advances Dalrymple, , p. The Lu-Hf method is now being effectively used to date certain rocks, especially meteorites Dalrymple, , p. As with any radiometric method, the ancient dates from the Lu-Hf method utterly refute the claims of young-Earth creationism. Therefore, it’s not surprising that Lu-Hf dating is yet another target for the wrath of young-Earth creationists.
Nevertheless, the only response that Woodmorappe , p. The Lu-Hf system is demonstrably sensitive to the mineralogy of magma sources in the mantle and crust. However, does this statement by Scherer et al. The answer is no. As with many of Woodmorappe’s quotations, when they are taken in context, they actually fail to support his antiquated claims. Specifically, the statements of Scherer et al. The Lu-Hf system is demonstrably sensitive to the mineralogy of magma sources in the mantle and crust As a result, the Lu-Hf system provides a view of crust-mantle evolution that is unique as compared to more commonly used isotopic systems such as Rb-Sr, Sm-Nd, and U-Pb.
Rather than undermining the reliability of the Lu-Hf method, the sensitivity of the method in identifying and dating magma sources is actually an asset!
Geochronology and Isotopic Mapping
New Lu—Hf and Pb—Pb age constraints on the earliest animal fossils. N2 – AbstractThe Neoproterozoic Doushantuo Formation, South China, preserves a unique assemblage of early multicellular fossils and overlies rocks, which are thought to have formed during an ice age of global extent. The age of this formation is thus critical for understanding the important biological and climatic events that occurred towards the end of the Proterozoic Eon.
Until now, direct dating of sedimentary formations such as the Doushantuo has been difficult and associated with large uncertainties.
The development of fast and reliable instrumental methods for U-Pb dating and Lu-Hf isotope anal- ysis of zircon has caused detrital zircon to become a popular.
The purpose of the Lu-Hf and U-Pb isotopic study was to better understand the Jurassic through early Tertiary magmatic and tectonic evolution of the Alaska Range and the significance of that magmatism for the formation of metallic mineral deposits. Didn’t find what you’re looking for? Suggest a dataset here. Home State of Alaska. Metadata Updated: April 3, License: No license information was provided. Visit page. Use Constraints: Any hard copies or published datasets utilizing these datasets shall clearly indicate their source.
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Tazzo-Rangel 1. The Lu-Hf isotope system is not only an important geo chronometer but also a powerful tool for petrogenetic studies. Besides being a powerful geochronometer for garnet-bearing meta-morphic rocks, especially eclogites e. In addition, when taken in combination with another isotopie system like Sm-Nd, mixing models can be calculated and deviations from the terrestrial trend can be identified e.
After the development of Multi-Collector Inductively Coupled Plasma Mass-Spectrometry MC-ICP-MS instruments in the early nineties, having a much greater ionization efficiency, as well as improvements in the chemical separation that diminished the is ob arie interferences and matrix effects of other major and trace elements Blichert-Toft et al. Recently, Sprung et al. This separation procedure facilitates additional separation of elements for other isotope systems like Rb-Sr and Sm-Nd from the same sample aliquot.
However, the contrasting chemical behavior of Lu and Hf, the content of refractory minerals like garnet, zircon or rutile in some igneous and metamorphic rocks, and the behavior of Hf from the spike, hampers the complete sample digestion and sample-spike equilibration. Problems with incomplete sample digestion by standard bench-top digestion methods were identified by various authors Blichert-Toft et al.
The system consists of one or two Teflon-coated pressure block s made of metal alloy that hosts 16 Teflon pressure vessels, a Teflon-coated hot plate, and a hot plate controller. Besides that, the system is equipped with an evaporation device, with which strong acids such as perchloric and hydrofluoric acid are evaporated and neutralized in a closed system with no need of a perchloric acid fume hood.
External reproducibility and accuracy of the methods is validated by analyses of several internation al reference standards and replicate analyses of unknown samples. Additionally, five single zircon grains and four fractions of amphibole concentrates were analyzed. A brief description of the samples is provided in Table 1.