Dating zircon grains Wep side xxx sex
Geochronological techniques measure radioactive isotope systems in specific minerals, dating major tectonic events that affected those minerals and therefore source rocks feeding the sedimentary system.
As a result detrital geochronology tends to produce several ‘populations’ of similar-aged minerals and these can be interpreted to provide highly diagnostic provenance information.
Zircon is ubiquitous in a wide variety of crustal rocks and sediments.
Its tendency to incorporate radioactive elements U and Th as well as low levels of Pb enables determinations of its crystallisation age to be determining using the U-Pb radioactive decay systems.
Do zircons—crystals of zirconium silicate—contain clocks you can trust?
Crystals of zirconium silicate can be found inside many sorts of rocks in the earth’s crust.
In contrast, destructive techniques such as LA-ICP-MS consume a large volume, leave a deep crater in the target grain, and often sample heterogeneous domains that are not visible and thus often yield discordant results which are difficult to interpret.
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.
In the case of metamorphic rocks this has been interpreted as inheritance of those zircon grains from the original sources of the sediments, the zircons somehow surviving metamorphism without resetting of the U-Pb isotopic system.
It has been successfully employed in siliciclastic sediments for mapping reservoirs in the basins, tracing sedimentary pathways, recording denudation histories and dating volcano-magmatic events.
This approach identifies characteristic detrital zircon age spectra, compares them with those from other stratigraphic units in the basin and matches them with potential sediment source areas.
In the laboratory, rock samples are crushed and the zircon grains are separated from the other minerals by heavy liquid and other mineral separation techniques.