Calibration of the lutetium-hafnium clock.
27 Jul 2001-Science (American Association for the Advancement of Science)-Vol. 293, Iss: 5530, pp 683-687
TL;DR: The existence of strongly unradiogenic hafnium in Early Archean and Hadean zircons implies that enriched crustal reservoirs existed on Earth by 4.3 billion years ago and persisted for 200 million years or more, and current models of early terrestrial differentiation need revision.
Abstract: Well-defined constants of radioactive decay are the cornerstone of geochronology and the use of radiogenic isotopes to constrain the time scales and mechanisms of planetary differentiation. Four new determinations of the lutetium-176 decay constant (lambda176Lu) made by calibration against the uranium-lead decay schemes yield a mean value of 1.865 +/- 0.015 x 10(-11) year(-1), in agreement with the two most recent decay-counting experiments. Lutetium-hafnium ages that are based on the previously used lambda176Lu of 1.93 x 10(-11) to 1.94 x 10(-11) year(-1) are thus approximately 4% too young, and the initial hafnium isotope compositions of some of Earth's oldest minerals and rocks become less radiogenic relative to bulk undifferentiated Earth when calculated using the new decay constant. The existence of strongly unradiogenic hafnium in Early Archean and Hadean zircons implies that enriched crustal reservoirs existed on Earth by 4.3 billion years ago and persisted for 200 million years or more. Hence, current models of early terrestrial differentiation need revision.
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Charles University in Prague1, University of Bergen2, Academy of Sciences of the Czech Republic3, University of Nottingham4, Boise State University5, Goethe University Frankfurt6, Memorial University of Newfoundland7, Stockholm University8, University of Vienna9, University of Geneva10, Swedish Museum of Natural History11
TL;DR: The Plesovice zircon as discussed by the authors has a concordant U-Pb age with a weighted mean Pb-206/U-238 date of 337.13 +/- 0.37 Ma (ID-TIMS, 95% confidence limits, including tracer calibration uncertainty).
3,694 citations
Cites methods from "Calibration of the lutetium-hafnium..."
...8648⁎10 (Scherer et al., 2001) and chondritic Hf composition ((176)Hf/(177)Hf=0....
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...…εHf values for all laser ablation and solution analyses were calculated assuming an age of 337 Ma and using a 176Lu decay constant of 1.8648⁎10−11 (Scherer et al., 2001) and chondritic Hf composition (176Hf/177Hf=0.282772) and 176Lu/177Hf ratio of 0.0332 from Blichert-Toft and Albarède (1997)....
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TL;DR: In this article, the first finding of continental crust-derived Precambrian zircons in garnet/spinel pyroxenite veins within mantle xenoliths carried by the Neogene Hannuoba basalt in the central zone of the North China Craton (NCC).
Abstract: We present the first finding of continental crust-derived Precambrian zircons in garnet/spinel pyroxenite veins within mantle xenoliths carried by the Neogene Hannuoba basalt in the central zone of the North China Craton (NCC). Petrological and geochemical features indicate that these mantle-derived composite xenoliths were formed by silicic melt^lherzolite interaction. The Precambrian zircon ages can be classified into three age groups of 2·4^2·5 Ga, 1·6^2·2 Ga and 0·6^1·2 Ga, coinciding with major geological events in the NCC. These Precambrian zircons fall in the field of continental granitoid rocks in plots of U/Yb vs Hf and Y. Their igneous-type REE patterns and metamorphic zircon type CL images indicate that they were not crystallized during melt^peridotite interaction and subsequent high-pressure metamorphism.The 2·5 Ga zircons have positive eHf(t) values (2·9^10·6), whereas the younger Precambrian zircons are dominated by negative eHf(t) values, indicating an ancient continental crustal origin.These observations suggest that the Precambrian zircons were xenocrysts that survived melting of recycled continental crustal rocks and were then injected with silicate melt into the host peridotite. In addition to the Precambrian zircons, igneous zircons of 315 3 Ma (2 ), 80^170 Ma and 48^64 Ma were separated from the garnet/spinel pyroxenite veins; these provide evidence for lower continental crust and oceanic crust recycling-induced multi-episodic melt^peridotite interactions in the central zone of the NCC. The combination of the positive eHf(t) values (2·91^24·6) of the 315 Ma zircons with the rare occurrence of 302^324 Ma subduction-related diorite^granite plutons in the northern margin of the NCC implies that the 315 Ma igneous zircons might record melt^peridotite interactions in the lithospheric mantle induced by Palaeo-Asian oceanic crust subduction. Igneous zircons of age 80^170 Ma generally coexist with the Precambrian metamorphic zircons and have lower Ce/Yb and Th/U ratios, higher U/Yb ratios and greater negative Eu anomalies.The eHf(t) values of these zircons vary greatly from ^47·6 to 24·6.The 170^110 Ma zircons are generally characterized by negative eHf(t) values, whereas the 110^100 Ma zircons have positive eHf(t) values.These observations suggest that melt^peridotite interactions at 80^170 Ma were induced by partial melting of recycled continental crust. The 48^64 Ma igneous zircons are characterized by negligible Ce anomalies, unusually high REE, U and Th contents, and positive eHf(t) values.These features imply that the melt^peridotite interactions at 48^64 Ma could be associated with a depleted mantle-derived carbonate melt or fluid.
2,753 citations
TL;DR: In this paper, the Lutetium-Hafnium radiogenic isotopic system is used as a chronometer and tracer of planetary evolution, and the Lu-Hf system parameters need to be more tightly constrained, in particular the LuHf isotopic composition of the chondritic uniform reservoir and, by extension, the bulk silicate Earth.
2,372 citations
TL;DR: In this article, the mean β Yb value of the individual spot and newly published Yb isotopic abundance data, six standard zircons and two standard baddeleyites, have been investigated using a Neptune MC-ICPMS, with 193 mm laser.
2,161 citations
TL;DR: In this paper, a cross-calibration of U-Pb and Lu-Hf isotopic systems on mineral fractions from the Proterozoic Karlshamn and Sorkka dolerites in Sweden and Finland is presented.
2,146 citations
References
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TL;DR: In this paper, the authors obtained a new set of present-day mean values in chondrites of176Hf/177Hf = 0.282772 ± 29 and176Lu/177 Hf= 0.0332 ± 2.
2,788 citations
TL;DR: New determinations of the half-lives of half-life values of $ −235 and −238 have been made improved techniques have allowed the halflife values to be measured with greater accuracy than has been heretofore achieved as discussed by the authors.
Abstract: New determinations of the half-lives of $^{235}\mathrm{U}$ and $^{238}\mathrm{U}$ have been made Improved techniques have allowed the half-life values to be measured with greater accuracy than has been heretofore achieved Samples were prepared by molecular plating and counted in a intermediate-geometry $\ensuremath{\alpha}$-proportional counter with an extremely flat pulse-height plateau The small amount of residual nonplated uranium was counted in a $2\ensuremath{\pi}$ counter Energy analysis with a silicon-junction detector was used to measure the presence of "foreign" activities For $^{235}\mathrm{U}$, the measured specific activity was (47981\ifmmode\pm\else\textpm\fi{}33) (dis/min)/(mg $^{235}\mathrm{U}$), corresponding to a half-life of (70381\ifmmode\pm\else\textpm\fi{}00048) \ifmmode\times\else\texttimes\fi{} ${10}^{8}$ yr For $^{238}\mathrm{U}$, the specific activity was measured as (74619\ifmmode\pm\else\textpm\fi{}041) (dis/min)/(mg $^{238}\mathrm{U}$), corresponding to a half-life of (44683\ifmmode\pm\else\textpm\fi{}00024) \ifmmode\times\else\texttimes\fi{} ${10}^{9}$ yr Errors quoted are statistical (standard error of the mean), based upon the observed scatter of the data This scatter exceeds that expected from counting statistics alone We believe that systematic errors, if present, will no more than double the quoted errors
2,543 citations
TL;DR: The discovery of a detrital zircon with an age as old as 4,404 ± 8 Myr is reported, about 130 million years older than any previously identified on Earth and represents the earliest evidence for continental crust and oceans on the Earth.
Abstract: No crustal rocks are known to have survived since the time of the intense meteor bombardment that affected Earth between its formation about 4,550 Myr ago and 4,030 Myr, the age of the oldest known components in the Acasta Gneiss of northwestern Canada. But evidence of an even older crust is provided by detrital zircons in metamorphosed sediments at Mt Narryer and Jack Hills in the Narryer Gneiss Terrane, Yilgarn Craton, Western Australia, where grains as old as approximately 4,276 Myr have been found. Here we report, based on a detailed micro-analytical study of Jack Hills zircons, the discovery of a detrital zircon with an age as old as 4,404+/-8 Myr--about 130 million years older than any previously identified on Earth. We found that the zircon is zoned with respect to rare earth elements and oxygen isotope ratios (delta18O values from 7.4 to 5.0%), indicating that it formed from an evolving magmatic source. The evolved chemistry, high delta18O value and micro-inclusions of SiO2 are consistent with growth from a granitic melt with a delta18O value from 8.5 to 9.5%. Magmatic oxygen isotope ratios in this range point toward the involvement of supracrustal material that has undergone low-temperature interaction with a liquid hydrosphere. This zircon thus represents the earliest evidence for continental crust and oceans on the Earth.
1,414 citations
TL;DR: In this article, the covariant behavior of Lu-Hf and Sm-Nd isotopes during most magmatic processes has been recognized, but the details of this behavior in the depleted mantle reservoir have not been adequately examined.
1,250 citations