Monazite dating

Polished thin sections of the host mineralized granite, SB-2671, and pegmatite with minor mineralization, SB-2670B, were selected for U-Th-Pb chemical monazite dating using to the method of Montel etal. (1996). 

Rubatto et al., 2001 Stem and Berman, 2001 Townsend et al., 2001). However, variable mineral dates also characterize many samples that show no obvious textural evidence of disturbance. In most cases, these dates differ in a predictable way (Hart, 1964 Armstrong et al., 1966 Wagner et al., 1977). For example, a typical amphibolite-facies pelitic schist will yield a (U-Th)/Pb monazite date older than its " °Ar/ Ar muscovite date, which will be, in turn, older than its " Ar/ Ar biotite date. Given the lack of textural evidence for other causes, the most likely mechanism to produce such inconsistencies is isotopic exchange between minerals and their surroundings. 

Montel, J.M., Foret, S., Veschambre, M., Nicollet, C. Provost, A. 1996. Electron microprobe dating of monazite. Chemical Geology, 131, 37-53. 

Monazite crystals within the ferrocarbonatite sample were dated using CHIME U-Th-Pb, and an age of 165 8 Ma was calculated. This age was used to evaluate the Sm-Nd ( nci= -6.0) and Rb-Sr ( Sr/ Sri65 = 0.71061) data these values are considerably different than the syenites and the sannaites. The high initial "sr/ Sr and low nci indicate that the... 

PI and P5 represent the age of the granite, and agree with previous dating (Rimsaite 1982). P3 represents the age of the pegmatite. P2 and P4 overlap and represent an event that reset monazite in both the granite and pegmatite, and corresponds to the age that Fowler Doig (1983) obtained by whole-rock Rb-Sr methods. 

The quartz-hosted monazite inclusions pre-date the muscovite leucogranite and are in the same range as Bevier Whalen s (1990a) U-Pb monazite age... 

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. 

Wilhgers B. J. A., Baker J. A., Krogstad E. J., and Peate D. W. (2002) Precise and accurate in situ Pb-Pb dating of apatite, monazite, and sphene by laser ablation multiple-collector ICP-MS. Geochim. Cosmochim. Acta 66, 1051-1066. 

Harrison T. M., McKeegan K. D., and EeEort P. (1995) Detection of inherited monazite in the Manaslu leucogranite by 208Pb/232Th ion microprobe dating crystallization age and tectonic significance. Earth Planet. Sci. Lett. 133, 271-282. 

Williams M. L., Jercinovic M. J., and Terry M. P. (1999) Age mapping and dating of monazite on the electron microprobe deconvoluting multistage tectonic histories. Geology 27, 1023-1026. 

Stern R. A. and Berman R. G. (2001) Monazite U-Pb and Th-Pb geochronology by ion microprobe, with an application to in situ dating of an Archean metasedimentary rock. Chem. Geol. 172(1-2), 113-130. 

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