Radiometric dating (age determination based on radioactive decay) is a key aspect of much research into past climate. Obviously, a past climate archive is of relatively limited use if the time period and time scale it is recording are unknown. The U-Th chronometer has proven extremely useful in this regard for geologically young materials (younger than ~500,000 years old), and one aspect of my work is to ensure the ongoing improvement of our U-Th analytical ability, and as importantly, to ensure that the uncertainties associated with the analyses are realistically estimated.
The U-Th chronometer suffers from the limitation that only materials less than ~500,000 years old can be dated. An alternative chronometer, the U-Pb system does not suffer with this limitation, and has been used successfully for several decades to date geologically old materials (up to the age of the Earth), but is analytically difficult to apply to young materials. One of the main projects that I am currently working on is to adapt and apply the U-Pb chronometer to geologically young carbonate materials in order to extend our geochronological ability beyond the ~500,000 year limit of the U-Th chronometer. A major aspect of this has been to develop and test a chemical extraction protocol capable of extracting the minute quantities of U and Pb from the samples to be dated, and to use this as a stepping stone to develop and test a simpler, more time-efficient method whereby samples are measured without pre-concentration of U and Pb. This is presently being applied to the dating of Siberian speleothems to constrain permafrost evolution.
Complementing the above, I am also developing data handling routines for the semi-automated processing of raw mass spectrometer data into corrected U/Th and U/Pb ratios. These corrected ratios form the basis of the age determination.
Unrelated to the above, I have also worked extensively on the tectonic evolution of the Lewisian Complex of the Outer Hebrides, NW Scotland.
View Selected Publications
- Liu, Y.-H., Henderson, G.M., Hu, C.-Y., Mason, A.J. , Charnley, N., Johnson K., Xie, S.- C. 2013. Links between the East Asian monsoon and North Atlantic climate during the 8,200 year event. Nature Geosciences, 6, 117-120
- Mason, A.J. 2012, Major early thrusting as a control on the Palaeoproterozoic evolution of the Lewisian Complex: evidence from the Outer Hebrides, NW Scotland Journal of the Geological Society, London, 169, 201–212.
- Mason, A.J. 2016 The Palaeoproterozoic anatomy of the Lewisian Complex, NW Scotland: evidence for two ‘Laxfordian’ tectonothermal cycles Journal of the Geological Society, London, xxx, xxx–xxx.
- Mason, A.J. & Brewer, T.S. 2004. Mafic dyke remnants in the Lewisian Complex of the Outer Hebrides, NW Scotland: a geochemical record of continental break-up and re-assembly. Precambrian Research, 133, 121-141.
- Mason, A.J. & Brewer, T.S. 2005. A re-evaluation of a Laxfordian terrane boundary in the Lewisian Complex of South Harris, NW Scotland. Journal of the Geological Society, London, 162, 401–407.
- Mason, A.J., & Henderson, G.M. 2010. Correction of multi-collector-ICP-MS instrumental biases in high-precision uranium–thorium chronology. International Journal of Mass Spectrometry, 295, 26-35.
- Mason, A.J., Henderson, G.M. & Vaks, A. 2013. An acetic acid-based extraction protocol for the recovery of U, Th and Pb from calcium-carbonates for U-(Th)-Pb geochronology. Geostandards and Geoanalytical Research, 37, 261-275.
- Mason, A.J., Parrish, R.R. & Brewer, T.S. 2004. U–Pb geochronology of Lewisian orthogneisses in the Outer Hebrides, Scotland: implications for the tectonic setting and correlation of the South Harris Complex. Journal of the Geological Society, London, 161, 45–54.
- Mason, A.J., Temperley, S. & Parrish, R.R. 2004. New light on the construction, evolution and correlation of the Langavat Belt (Lewisian Complex), Outer Hebrides, Scotland: field, petrographic and geochronological evidence for an early Proterozoic imbricate zone. Journal of the Geological Society, London, 161, 837–848.
- Thomas, A.L., Fujita, K., Iryu, Y., Bard, E., Cabioch, G., Camoin, G., Cole, J.E., Deschamps, P., Durand, N., Hamelin, B., Heindel, K., Henderson, G.M., Mason, A.J., Matsuda, H., Ménabréaz, L., Omori, A., Quinn, T., Sakai, S., Sato, T., Sugihara, K., Takahashi, Y., Thouveny, N., Tudhope, A.W., Webster, J., Westphal, H., Yokoyama, Y., 2012 Assessing subsidence rates and paleo water-depths for Tahiti reefs using U-Th chronology of altered corals, Marine Geology, 295-298, 86-94
- Thomas, A. L., Henderson, G. M., Deschamps, P., Yokoyama, Y., Mason, A. J., Bard, E., Hamelin, B., Durand, N., & Camoin, G., 2009. Penultimate Deglacial Sea-Level Timing from Uranium/Thorium Dating of Tahitian Corals. Science, 324, 1186-1189.
- Vaks, A., Gutareva, O.S., Breitenbach, S.F.M., Avirmed, E., Mason, A.J., Thomas, A.L., Osinzev, A.V., Kononov, A.M., & Henderson, G.M. 2013. Speleothems reveal 500 kyr history of Siberian permafrost. Science, 340, 183-186