U-Pb Dates

More recently, Encamacion and Grunow (1996) reported a U-Pb date of 515 8 Ma for zircon in the equigranular and unfoliated granite of the Cooper Nunatak in the Brown Hills (see below). This date is compatible with the ArP Ar dates of biotites and hornblende reported by Felder and Faure (1990) and further constrains the time of intrusion and crystallization of the granite plutons in the Brown Hills. 

Th-Pb methods of dating igneous and metamor-phic rocks is based on the decay of the isotopes of uranium and thorium to stable isotopes of lead  

Vocke and Hanson (1981) also dated zircons which they extracted from samples of the Vida Granite and the Olympus Granite-Gneiss in core 6 recovered by the 

Different size fractions of the zircons extracted by Vocke and Hanson (1981) from the Vida Granite in DVDP6 define a chord that intersects the concordia curve at 447 34 Ma and at 0 Ma. The upper intercept is the crystallization age of zircon in the Vida Granite and the lower intercept (0 Ma) indicates that the zircons may have been losing radiogenic lead by continuous diffusion as a result of chemical weathering. 

Size-fractions of zircon extracted from a pluton of unfoliated quartz diorite which intrudes the intensely folded metasedimentary rocks of the Anthill and Cocks formations in the Skelton Glacier-Cocks Glacier area at 78°39 and 161°00 E, were dated by Rowell et al. (1993) by the U-Pb method. The data define a chord that intersects concordia at a point that corresponds to a well-constrained date of 551 4 Ma. Zircon from a second pluton, composed of granite and located only 1 km from the quartz-diorite pluton, yielded an identical date of 551 4 Ma (Encarnacion and Grunow 1996). This date not only establishes the age of the two plutons, but also sets a lower limit to the time of deposition and deformation of the metasedimentary rocks that were intruded by these plutons. 

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Jones CE, Halliday AN, Lohmann KC (1995) The impact of diagenesis on high-precision U-Pb dating of ancient carbonates An example from the Late Permian of New Mexico. Earth Planet Sci Lett... 

Wendt I, Carl C (1985) U/Pb dating of discordant 0.1 Ma old secondary U minerals. Earth Planet Sci Lett 73 278-284... 

The discovery of the decay chain, of course, started with the seminal work of Marie Curie in identifying and separating Ra. Through the work of the Curies and others, all the members of the decay chain were identified. An important milestone for geochronometrists was the discovery of °Th (called Ionium) by Bertram Boltwood, the Yale scientist who also made the first age determinations on minerals using the U-Pb dating method (Boltwood in 1906 established the antiquity of rocks and even identified a mineral from Sri Lanka-then Ceylon as having an age of 2.1 billion years )... 

In K-Ar or zircon U-Pb dating, modeling the loss of radiogenic isotopes by volume diffusion is important. If P0 is the local concentration at t = 0 of a radioactive element decaying with constant X, a source term exists in the transport equation of the radiogenic element which is the local rate of accumulation AP0e Xt. For dual decay,... 

The footwall units below the ore horizon include the Watson Lake Rhyolite and the Bell River Complex intrusion. Both have U-Pb dates of 2724 Ma (Mortensen 1993), and the Bell River Complex is considered to the heat source which drove the hydrothermal circulation that created the ore deposits. 

The Sm-Nd data were used to create an isochron, which was used to derive and age (Fig. 1). The calculated age, 369 19 Ma, is in excellent agreement with the known age of the complex, 368 4 Ma (Parrish et al. 1987). This age is also consistent with our preliminary LA-ICP-MS zircon U-Pb dating of dykes in the SM and the NS-N groups. 

Liu, J. et al. 2008. Zircon LA-ICPMS U-Pb dating of Hukeng granite in Wugongshan area,Jiangxi Province and its geochemical characteristics[J]. Acta Petrologica Sinica, 24(8), 1813-1822. 

Basement-hosted uranium oxides from Athabasca Basin mineraiogy, U/Pb dating, major and Rare Earth Eiement (REE) concentrations comparison with U-oxides from deposits iocated in the vicinity of the... 

Keywords Athabasca, uranium deposits, U-Pb dating, REE, basement-hosted... 

Isotopic U/Pb dating of basement-hosted uranium oxides... 

This method has been most widely used in (i) the °K- °Ar system, (ii) the U-Th-He system, (iii) the U-Pb dating of zircon, and (iv) the U-Th-Pb dating of monazite using electron microprobe measurements. The last is a developing method with large errors because of the low analytical precision and because isotopes are not measured. 

Figure 5-6 The concordia and an example of discordia for U-Pb dating. The x-axis is The y-axis is ° Pb / U. The...

Wetherill s concordia diagram for interpreting discordant U-Pb dates caused by episodic loss of radiogenic lead. 

A sensitive high resolution ion microprobe (SHRIMP, with a maximum mass resolution of m/Am of 30 000) was designed on the basis of the double-focusing sector field Matsuda type instrument190 as discussed by Compston in 1996.191 The first SHRIMP and a modified version for precise isotope ratio measurements were constructed in the 1980s and later produced commercially.192 The main application of this instrument so far has been in situ U-Pb dating of zircon.192,193... 

Figure 1 Studies published between 1988 and 1997 reporting use of secondary ion mass spectrometry (SIMS) in geochemistry and cosmochemistry. Papers are subdivided according to theme Hvy Iso, studies of heavy isotope ratios, principally for U-Pb dating Lt Iso, studies of light stable isotope ratios (H, B, C, O, S) Hvy El, studies primarily focused on analysis of elements >40 amu (e.g., rare earth elements) Lt El, studies primarily focused on analysis of elements <40 amu (e.g., water content) Prec Met, analysis of precious metal contents (e.g., Au, Ag, Pt) Expt, analysis of experimental run products Misc, other mis-cellanous studies utilizing SIMS.

LA-ICP-MS using a multi-collector instrument for Pb-Pb dating via ° Pb/ °" Pb and ° Pb/ ° Pb isotope ratio measurements of natural rutile crystals has been utilized to study geological temperature-time histories. The significance of Devonian-Carboniferous igneous activity in Tasmania on the basis of U-Pb dating has been measured by sensitive high resolution ion microprobe (SHRIMP). ... 

Gopel C., Manhes G., and AUegre C. J. (1991) Constraints on the time of accretion and thermal evolution of chondrite parent bodies by precise U-Pb dating of phosphates. Meteoritics 26, 73. 

Terada K., Saiki T., Hidaka H., Hashizume K., and Sano Y. (2002) In-situ ion microprobe U-Pb dating of glass spherules from Apollo 17 lunar soils. In Lunar Planet. Sci. XXXIII, 1481. The Lunar and Planetary Institute, Houston. 

Chen Y. D., O Reihy S. Y., Griffin W. L., and Krogh T. E. (1998) Combined U-Pb dating and Sm-Nd studies on lower crustal and mantle xenohths from the delegate basaltic pipes, southeastern Austraha. Contrib. Mineral. Petrol. 130(2), 154-161. 

Brown S. J. A. and Fletcher I. R. (1999) SHRIMP U-Pb dating of the preemption growth history of zircons from the 340 ka Whakamaru Ignimbrite, New Zealand evidence for >250 ky magma residence times. Geology 27, 1035-1038. 

Sano Y. J., Tsutsumi Y., Terada K., and Kaneoka 1. (2002) Ion microprobe U—Pb dating of quaternary zircon implication for magma cooling and residence time. J. Volcanol. Geotherm. Res. 117, 285—296. 

Kosler J., Fonneland H., Sylvester P., Tubrett M., and Pedersen R. B. (2002) U—Pb dating of detrital zircons for sediment provenance studies a comparison of laser ablation ICPMS and SIMS techniques. Chem. Geol. 182(2—4), 605-618. 

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