Developing the cosmogenic He chronometer

Dymock, Ross Campbell (2014) Developing the cosmogenic He chronometer. MSc(R) thesis, University of Glasgow.

Abstract

Helium isotopes have found wide use in geoscience research, notably as chronometers of surface exposure. This thesis comprises two distinct components around the theme of cosmogenic He determinations. In the first section (Chapter 3) I test whether cosmogenic 3He can be used to determine short exposure times (<30 ka) in volcanic rocks that are significantly older than the exposure time (~60 Ma). Helium isotopes were measured in olivine, ilmenite and plagioclase from early Tertiary basalts from Isle of Skye, Scotland in order to determine exposure ages. Correction for radiogenic He was made with three different methods. The upper limit of exposure ages are variable, and slightly lower than previously determined by 36Cl (Stone et al. 1998).

In the second part of the thesis I report characterisation of the new ThermoScientific HELIX-SFT mass spectrometer then compare performance against the existing MAP 215-50 instrument. The reproducibility of helium isotope determinations using the HELIX-SFT (~0.78%) is significantly better than the MAP 215-50, though not as good as reported elsewhere. The reasons for this are discussed and the potential for further improvements are highlighted.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Keywords: Cosmogenic helium, noble gas mass spectrometry, cosmogenic dating, Isle of Skye Scotland
• Subjects: Q Science > QE Geology
• Colleges/Schools: College of Science and Engineering > School of Geographical and Earth Sciences > Earth Sciences
• Supervisor's Name: Stuart, Professor Fin
• Date of Award: 2014
• Depositing User: Mr Ross Dymock
• Unique ID: glathesis:2014-5287
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 08 Jul 2014 14:16
• Last Modified: 08 Jul 2014 14:17
• URI: https://theses.gla.ac.uk/id/eprint/5287