Zircon dating metamorphic rocks formed

zircon dating metamorphic rocks formed

At present, Chemostrat can determine U-Pb ages for zircon and apatite crystals. Zircon is a robust mineral and so the crystals preserve the age at which they formed or underwent high grade metamorphism. Consequently, U-Pb zircon geochronology can be employed to constrain the age of the basement rocks and in turn can help to identify sediment dispersal patterns and to correlate sandstones.

By determining the U-Pb isotopic composition of a zircon crystal, the age of the crystal can be calculated by utilising a ‘concordia diagram’. If the analysed zircon crystal has not suffered either Pb loss or U gain, it will plot on the concordia line from which its age can be deduced. If, however, a zircon crystal has lost Pb, one can still calculate its age by plotting the data on a ‘discordia line’ instead.

Sandstones frequently contain detrital zircon grains and if these grains are undisturbed and concordant, their ages provide some clue as to their provenance. Generally at least fifty grains from each sandstone sample need to be analysed in order to obtain reliable data.

The age of apatite grains can be calculated by plotting their U-Pb isotopic composition to form a discordia line. Apatite has a lower closure temperature than zircon, i.e., ~400 - 500°C, and so are more easily ‘reset’ by heating than zircons. Therefore, they provide different information about the source of sandstones than zircons such as low grade metamorphic rocks. This provides further information about sediment input pathways to sedimentary basins and, when combined with detrital zircon analysis, provides a powerful tool to identify the provenance of sediments.

Ms. Rubatto and Mr. Moeller, I am interested in papers that discuss the zircon grains characteristics which might help reavealing the zircon sources. Can you suggest some?



SHRIMP Zircon U-Pb Dating of Sapphirine-Bearing Granulite.

Ms. Rubatto and Mr. Moeller, I am interested in papers that discuss the zircon grains characteristics which might help reavealing the zircon sources. Can you suggest some?