Please note that Internet Explorer version 8. Please refer to this blog post for more information. Recent advances in the field of geochronology have led to a greater understanding of fo scale and duration of geological processes. It is currently possible to date igneous and metamorphic rocks by a variety of radiometric methods to within a million years, but establishing the depositional age of sedimentary rocks has remained exceedingly difficult.
The problem is most pronounced for Precambrian rocks, where the low diversity and abundance of organisms have prevented the establishment of any meaningful biostratigraphic framework for correlating strata. Also, most Ricks successions have been metamorphosed, rendering original minerals textures difficult to interpret, and resetting ot minerals.
Xenotime YPO 4 is an isotopically robust chronometer, which is increasingly being recognized as a trace constituent in siliciclastic sedimentary rocks. It may start to grow during early diagenesis, typically forming syntaxial outgrowths on detrital zircon grains. Diagenetic xenotime occurs in a wide variety of rock types, including conglomerate, sandstone, siltstone, shale, phosphorite and volcaniclastic rocks, varying from early Archaean to Mesozoic absolite age. The formation of diagenetic xenotime is principally related to redox cycling of Fe-oxyhydroxides and microbial decomposition of organic matter, leading to elevated concentrations of dissolved phosphate and rare earth elements Sedimeentary in sediment pore-waters.
In addition, it has an exceptional ability to remain closed to element mobility during later thermal events, and commonly yields concordant and precise dates. In metamorphosed sedimentary rocks, diagenetic xenotime retains its age information up to lower amphibolite facies in sandstone, and up to mid-upper greenschist facies in pelitic rocks. In many Precambrian basins e. With the aid of petrography, geochemical microanalysis and the use of isotopic techniques with fine spatial resolution, it may be possible to use xenotime to date early diagenesis, and potentially every major fluid and thermal rating to lf affected a depositional basin.