Dr Yuri Amelin
Research School of Earth Sciences
The Australian National University
Tel: +61 2 612 50831
Fax: +61 2 612 50941
- Isotopic dating (geochronology) of terrestrial and extraterrestrial materials and processes.
- Advancement of techniques for isotope analysis.
- Formation and early evolution of our Solar System.
- Early evolution of the Earth's crust and mantle.
- Refining decay constants and other fundamental parameters of radiogenic isotope geochemistry.
- Migration and partitioning of elements.
- Disequilibrium in U and Th decay series, and its application as a geochronometer and isotopic tracer.
- Radiation effects in solids.
What is geochronology?
Geochronology is the science of determining the ages of rocks, minerals and other materials from the Earth and other Solar System bodies. The ages are determined by measuring the amounts of a radioactive isotope with a known half-life and its decay product. Geochronology allows us to determine which of the geological events close in time occurred first, and thus to constrain their causal relations. It also enables us to measure the rates of geological processes that occurred in the past.
With precision of dating of 0.1-0.2 million years, we can verify the links between mass extinctions and impact events or catastrophic volcanic eruptions, pinpoint geological processes responsible for formation of major ore deposits, and study other important natural processes that occurred billions of years ago. This cannot be done reliably with less precise dating techniques. Better understanding the evolution of the Earth and the Solar System relies on our ability to measure natural isotopic variations of elements spanning the range of the periodic table, with ever higher precision from ever smaller samples.
SHRIMP and SPIDE2R
The approach to U-Pb dating, currently adopted by the Australian geological community, mainly relies on SHRIMP (Sensitive High Resolution Ion Microprobe). A 10-30 µm sample area, sputtered by the primary ion beam, gives an unparalleled spatial resolution, making it possible to resolve age differences within a 50-100 µm mineral grain. The downside of the high spatial resolution is that only a small number of ions reach detectors, hence the uncertainty of the dates is relatively large.
In order to achieve high precision of dates with the U-Pb and other isotopic chronometers, we started constructing the SPIDE2R facility (Sensitive and Precise Isotopic Dating of Earth’s and Extraterrestrial Rocks). The highest possible precision and accuracy of dating will be assured by using the most sensitive thermal ionisation mass spectrometer with upgraded source and ion detection systems, optimisation of ionisation procedures, new clean labs for processing terrestrial and extraterrestrial samples with minimum contamination, and accurate correction of mass fractionation using double spikes such as 202Pb-205Pb-233U-236U.