Details of Award
NERC Reference : NE/J013242/1
A new approach to (U-Th)/He thermochronometry: exploiting the natural dispersion of single grain ages to obtain robust thermal history information
Grant Award
- Principal Investigator:
- Professor RW Brown, University of Glasgow, School of Geographical & Earth Sciences
- Co-Investigator:
- Professor FM Stuart, Scottish Universities Env Research Cen, SUERC
- Co-Investigator:
- Dr SM Roper, University of Glasgow, School of Mathematics & Statistics
- Grant held at:
- University of Glasgow, School of Geographical & Earth Sciences
- Science Area:
- Earth
- Overall Classification:
- Earth
- ENRIs:
- Environmental Risks and Hazards
- Global Change
- Natural Resource Management
- Science Topics:
- Palaeoenvironments
- Sediment/Sedimentary Processes
- Tectonic Processes
- Abstract:
- Geochronology, the science of dating rocks and fossils and determining the time sequence of events in the history of the Earth, underpins modern, quantitative geology. Traditional paleontological and biostratigraphic correlation methods are the most common relative dating methods used by geologists. But, to establish quantitative dates and rates of processes an absolute time frame is required. Absolute, or numeric, dating involves methods of determining the geologic age of a fossil, rock, or geologic event in units of time, usually years. These absolute methods establish the ages of samples by measuring the amount of a specific radioactive isotope (the parent) within the sample as well as the amount of the stable product arising from the radioactive decay (the daughter isotope). For example, the U-Pb technique measures how much 238-U (the parent) is present and how much 206-Pb (the daughter) has been formed by radioactive decay of 238-U, and by knowing the rate of radioactive decay of 238-U we can calculate the age of the sample. The science of thermochronometry extends the practice of geochronology by determining the temperature a rock sample experienced at a particular time, or times, in the past, i.e. the rock's thermal history. Because subsurface temperatures increase systematically with depth within the Earth the thermal history of a sample collected at the surface records the sample's trajectory from depth to the surface. Thermochronometry thus enables geologists to study and quantify a whole range of processes that are important to understanding how the Earth evolved, such as when and how fast mountain ranges are created and destroyed or quantifying the mass of solid and chemical material transported from continents to the oceans by rivers. One of the most widely used thermochronometry techniques is based on measuring the amount of Helium (the daughter product) resulting from the radioactive decay of 238-U and 232-Th in a mineral called apatite and it is known as the (U-Th)/He technique. This technique is now commonly used to determine thermal histories of rocks in geoscience investigations across an extremely wide range of geological settings because of it is sensitive to relatively low temperatures (c. 40-70 C). For a range of reasons it is now standard practice to analyse individual grains of apatite extracted from a sample, and an analysis is deemed reliable when 2 or 3 (or more) grain ages from the same sample are statistically equivalent, i.e. the individual grain ages are the same (once size and composition are accounted for). In many studies though it has been shown that single grain ages from the same sample are commonly not the same, and in fact are highly dispersed. This is thought to arise from heterogeneous U and Th distribution within grains, He being added to the grain for from outside grain boundaries (so called excess He) or from differences in the size of grains or in the rate that He diffuses out of the grains at any given temperature caused by accumulation of radiation damage to the apatite crystals. However, in many cases, the observed dispersion is shown to be unrelated to these known effects. We believe we have discovered the underlying reason for why this kind of dispersion occurs, and our initial experiments indicate it is a natural consequence of analysing crystals that have been broken during the rock crushing and mineral separation process. The exciting consequence of our discovery is that, rather than a hindrance to the technique, this dispersion contains valuable information about a sample's thermal history. In this project we aim to demonstrate and fully test a novel new approach to extracting the thermal history information and applying this widely used thermochronometry technique which we believe will resolve decades of uncertainty about the origin of the 'cryptic' dispersion of single grain ages, and will vastly extend the applicability of this powerful analytical method.
- NERC Reference:
- NE/J013242/1
- Grant Stage:
- Completed
- Scheme:
- Small Grants (FEC)
- Grant Status:
- Closed
- Programme:
- Small Grants
This grant award has a total value of £41,930
FDAB - Financial Details (Award breakdown by headings)
| DI - Other Costs | Indirect - Indirect Costs | DA - Investigators | DA - Estate Costs | DI - Staff | DA - Other Directly Allocated | DI - T&S |
|---|---|---|---|---|---|---|
| £6,896 | £6,804 | £11,179 | £1,880 | £5,073 | £7,239 | £2,861 |
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