Zircon age dating
For the example to the right, offset values for Centering the secondary ion image in the center of the field aperture (FA) is necessary for each new analysis spot because primary beam paths and conditions of secondary ion extraction vary over the area of the sample surface,in particular when spot-to-spot movements over large distances (few mm) are required.
The sequence is as follows: In order to stabilize the secondary ion signal and to remove surface contamination, the primary beam is focused on the sample surface for a certain time period prior to data acquisition.
The most common dating method involves the use of minerals like zircon and monazite that are relatively common in granitic rocks.
Zircon is especially useful because it frequently contains uranium in substitution for zirconium, but does not incorporate lead (as shown by the absence of Lead-204).
Isotopic ratios are then calculated using raw intensities corrected for electron multiplier dead-time and drift-corrected mid-analysis values.
The uranium and thorium decay systems offer a multitude of radiometric dating options.
The cores are enriched in REE, Y, Th and U and are characterized by distinctly flatter REE patterns in contrast to those of the rims and transparent homogenous crystals.Zircon from the different stratigraphic units has specific Th/U ratios, the highest of which (1.5–4) occurs in a Merensky Reef zircon core.The Ti content of Bushveld zircon ranges from 12 to 52 ppm correlating to a crystallization temperature range of 760–930 °C. Selector .selector_input_interaction .selector_input. Selector .selector_input_interaction .selector_spinner. At present, Chemostrat can determine U-Pb ages for zircon and apatite crystals.
Uranium 238 decays through a series of steps to Lead 206.