Even as early as 1960 Tilton reported that Pb diffuses from zircon and U-bearing minerals at temperatures as low as 50°C. This is dramatically illustrated by the contact metamorphic effects of a Tertiary granite stock on zircon crystals in surrounding regionally metamorphosed Precambrian sediments and volcanics.demonstrated that unzoned crystals can be the result of recrystallization of zoned crystals accompanied by loss of U, Th, and Pb, and "resetting" of the U-Pb "ages." Such recrystallization can be due to subsequent regional metamorphism. found that high-grade metamorphism of granitic and related rocks reduced their U-Pb zircon "ages" from 1000 Ma down to 540 Ma, with zircons even from a single sample yielding U-Pb "ages" between 1072 Ma and 539 Ma. Yet another significant problem for zircon U-Pb "dating" is the discovery in some metamorphic and granitic rocks of zircon crystals that yield much older "ages" than the accepted ages of the rocks.The most common application of the instrument is in uranium-thorium-lead geochronology, although the SHRIMP can be used to measure some other isotopic and elemental abundances.trying to build an ion microprobe at the Research School of Earth Sciences of the Australian National University that exceeded the sensitivity and resolution of ion probes available at the time in order to analyse individual mineral grains. Growing interest from commercial companies and other academic research groups, notably Prof.*Prices in US$ apply to orders placed in the Americas only.Prices in GBP apply to orders placed in Great Britain only.
Three situations may be met: (1) monazites exhibiting significant Th/U ratio variation, (2) monazites exhibiting a fairly constant Th/U ratio, but significant U Th heterogeneity, and (3) monazites of constant U and Th concentrations.
Recent improvements in the statistical treatment of many in situ data now make it possible to decipher the related thermal events and so obtain reliable and precise ages.