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Dating zircon grains

Radioisotopic dating of detrital minerals in sedimentary rocks can constrain sediment sources (provenance), elucidate episodes and rates of ancient orogenesis, and give information on paleogeography and sediment-dispersal patterns.

Why is it that different locations within a zircon have differing ratios of Pb/U?

Certainly it doesn’t make sense to say different zones within a tiny crystal formed at vastly different times.

Pb found in zircon is not common Pb from magma, but radiogenic Pb produced within the crystal after it formed.

So to answer the question posed in the title, we should not assume that there had been different amounts of common Pb incorporated during crystallization.

Th activity was measured to be varying from 2.0 to 2.8.

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  1. Nov 15, 2002. Only zircon grains which are transparent are suitable for the dating method. These do not absorb the light from the thermoluminesence. The researchers developed a new selection installation to select these 'zircon jewels' from the zircon fraction in the sand, in which coloured and sometimes dark grains.

  2. A single grain of zircon may contain different compositions and ages. Using these methods, the geologists determine if they want to examine the entire grain of zircon or certain parts of it to date only a certain spot. Another option is to dissolve the zircon grain in hydrofluoric acid to separate the uranium and the lead.

  3. Apr 13, 2014. A novel approach of thermally annealing and sequentially partially dissolving single zircon grains prior to high- precision Isotope Dilution Thermal Ionization Mass Spectrometry ID-TIMS is presented. This technique is applied to complex zircon from the Precambrian Lewisian Gneiss Complex of Scotland.

  4. Zircon Detrital zircon U-Pb geochronology is a powerful technique used for studies of sand and sandstone provenance. 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.

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