Dr. Yona Nebel-Jacobsen - Honours Projects

In-Situ Age Characterization of Mica Standards

Supervisor(s): Yona Nebel-Jacobsen

For mass spectrometry analyses of any kind, good characterized standards are of paramount importance. They are used to normalize data and ensure the quality of analyses. When developing new techniques and analytical protocols, analyses of internationally accepted standards is a good way to show the capabilities of the new routine.

Rubidium-Strontium (Rb-Sr) dating of mica is a standard tool in geochronology. 87Rb decays to 87Sr, making it possible to determine the age of minerals with a high Rb-Sr-ration, like mica. Due to the same mass of the relevant isotopes, a resolution between both elements is not possible at the same time in a standard mass spectrometer. This is why the sample has to be dissolved first, subsequently followed by a wet chemistry separation, to separate all Rb from the Sr of the sample, in order to run both elements separately on a mass spectrometer. This is a time consuming process.

The Isotopia facility at SEAE houses a so called ‘triple quadrupole mass spectrometer’, which has a reaction cell. In this reaction cell, certain gases are used to initialize reactions between some elements with components of the gas. Applied to the Rb-Sr system, Rb reacts with O-bearing gases, but Sr does not. As this reaction changes the mass of Rb (it has now formed a complex which has a higher mass), it is then possible to analyze Rb and Sr isotopes at the same time. This enables the in-situ dating of mica.

The aim of this Honours project would be to analyze several different standards, which are very well characterized using other, more traditional, dating tools, with this new technique. The results can be compared to the published values, to allow an evaluation of the technique.

During the project, the Honours candidate will learn how to prepare a sample for laser ablation analyses, operate the laser system and the iCapTQ mass spectrometer. No field work is required. A general interest in analytical geochemistry is desirable, as well as a basic understanding in mineral chemistry.

For further information contact: Yona Nebel-Jacobsen