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The Australian National University

U-Th accessory minerals

A number of accessory minerals can be dated by the U-Th-Pb system to obtain a precise age. At RSES, precise U-Pb ages of crystal domains are measured either by SHRIMP ion microprobe or by Laser Ablation - ICPMS .

Ages can then be correctly interpreted in geological terms if the environment and conditions of formation (pressure, temperature, fluids, deformation etc.) of the dated mineral are known. The trace elements composition of minerals such as zircon, monazite, titanite, allanite and rutile can vary according to coexisting minerals and thus provide information on condition in which the mineral formed.

Titanium in zircon can provide accurate temperature estimates of crystallization. Partitioning of trace elements between zircon and garnet can for example directly related the age obtained from zircon with the pressure-temperature information obtained from the coexisting garnet. Other isotopic systems such as oxygen and hafnium can assist in determining the source of the dated mineral zone.

Absolute age combined with this additional information provides a powerful tool to reconstruct rocks evolutions over time and describe important geological processes.

Updated: 16 December 2011/ Responsible Officer:  Director / Page Contact:  Webmaster