Zircon dating metamorphic rocks

Posted by / 02-Jul-2017 11:45

These types of minerals often produce lower precision ages than igneous and metamorphic minerals traditionally used for age dating, but are more common in the geologic record.During the alpha decay steps, the zircon crystal experiences radiation damage, associated with each alpha decay.Thus the current ratio of lead to uranium in the mineral can be used to determine its age.The method relies on two separate decay chains, the uranium series from Pb) leads to multiple dating techniques within the overall U–Pb system.Undamaged zircon retains the lead generated by radioactive decay of uranium and thorium until very high temperatures (about 900 °C), though accumulated radiation damage within zones of very high uranium can lower this temperature substantially.

The above-mentioned results indicate that the Precambrian crystalline basement (1808–1873 Ma) exists in the southern Songliao Basin and could be related to tectonic thrust, and that the Early Paleozoic (424–490 Ma) and Late Paleozoic magmatisms (264–292 Ma) also occur in the basin basement, which are consistent with the ages of the detrital zircons from Bi-Act-Q schist in the basement.A concept for the interpretation of the initial provenance signal in rocks of the Taratash block (in the Southern Urals) using the zircon isotope dating of the Archean and Early Proterozoic igneous and metamorphic rocks was substantiated and carried out.Based on 132 zircon-age datings with a discordance of as much as 10%, a probability-density diagram was compiled first to compare these age data with those of detrital zircons from Lower Riphean sandstones of the Ai Formation and, secondly, with the probability density of zircon ages in metamorphic rocks of the Aleksandrovsk block, which is located to the east.The term U–Pb dating normally implies the coupled use of both decay schemes in the 'concordia diagram' (see below).However, use of a single decay scheme (usually Pb) leads to the U–Pb isochron dating method, analogous to the rubidium–strontium dating method.

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Their U-Pb isotopic ages are 1808±21 Ma and 1873±13 Ma, respectively.

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