U-Pb dating of zircon

Model ages of granitoids may be used to estimate the age of their source. In the case of mantle-derived granites, the model age gives the time of mantle fractionation 

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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. 

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... 

In addition, the U-Pb date of zircons in the gabbro of the Cotton Plateau (668 1 Ma) implies that Rodinia broke up somewhat later and that the rift valley between Laurentia and the East Antarctic craton began to trap sediment later than the previous interpretation of the evidence had indicated. The reassignment of the bulk of the Goldie Formation to the Starshot Formation of the Byrd Group also means that the contact between the inboard part of the Goldie Formation and the over-lying Shackleton Limestone is now presumed to be an unconformity. 

The U-Pb dates of zircons in granites on ML Webster and in the Berry Peaks (494 3 and 480 5 Ma, respectively) indicate that the age of these granites is Early Ordovician and that they crystallized at the end of the Ross Orogeny. The gneisses in the Fallone Nunatak contain old xenocrystic zircons that may have been derived from Neoproterozoic Grenville basement that could have existed in the crustal magma sources off-shore of the paleo-Pacific coast of the present Transantarclic Mountains (McKenna etal. 1994 Dalziel 1992). 

Table 6.8 U-Pb dates of zircon and monazite in rhyolites of the Leverett Formation and the Granite Harbor Intrusives in the nunataks north of the Leverett Glacier, Queen Maud Mountains (Van Schmus et til. 1997 Rowell et til. 1993 Davis and Blankenship 2005)...

The U-Pb date of zircon from the Gorecki Felsite (5(X) 8 Ma) confirmed that the age of the Patuxent Formation in the Schmidt Hills is in fact. Middle to Late Cambrian according to the geologic timescale of the lUGS (2002). 

U-Pb dates of zircon by Gose et al. (1997) indicated a date of 1,112 4 Ma for a Littlewood rhyolite and 1,113.5 + 18,-6Ma ofaBertrab granophyre. Asample of titanite at Bertrab has a U-Pb date of 1,106 3 Ma which Gose et al. (1997) interpreted as a cooling age and which indicates that the rocks cooled rapidly after crystallization from magma. 

Frei, D. and Gerdes, A. (2009) Precise and accurate in situ U-Pb dating of zircon with high sample throughput by automated LA-SF-ICP-MS. Chem. CeoL, 261, 261-270. 

Simonetti, A., Heaman, L.M., Chacko, T., and Banerjee, N.R. (2006) In situ petrographic thin section U-Pb dating of zircon, monazite, and titanite using laser ablation-MC-ICP-MS. Int. J. Mass Spectrom., 253 (1-2), 87-97. 

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