Accessory minerals such as zircon and monazite are used to understand the timing and rate of geological processes. Using radioactive decay of uranium (U) and thorium (Th) into different isotopes of lead (Pb) within monazite crystals (CePO4) is one of the most popular methods for dating ancient rocks. However, minerals are affected by physical and chemical processes that promote decoupled mobility of parent (U, Th) and daughter (Pb) elements this will increase the uncertainty of this dating method. This mobility within monazite may leave traces only detectable at the nanometer scale.
Napier Complex monazite crystals containing nanoinclusions of galena (PbS) were analyzed by atom probe tomography at Curtin University (Perth, Australia). These analyses revealed that the isotopic composition of the two minerals is consistent with two events of Pb mobility with partial retention of radiogenic Pb within nanocrystals of the galena. These events are dated between 1 billion and 500 million years and reflect large-scale geological events at these times. Atom probe tomography provides a major advance in the understanding of such mechanisms and for the development of nano-geochronology.
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