This study presents a detailed consideration of the effects of geometry, U- and Th-zonation and diffusion on zircon (U-Th)/He ages. The errors introduced by assuming homogeneity are quantified, and the difficulties associated with the characterisation of U and Th zonation in zircon samples are addressed in a qualitative and quantitative assessment. When these issues are fully considered, the (U-Th)/He age distribution of unknown samples can be understood, and (U-Th)/He ages can be interpreted with confidence. Using these more rigorous interpretive techniques, it has been possible to accurately determine the (U-Th)/He ages of zircons from the Palaeogene Hebridean Igneous Province. This data has been used in conjunction with apatite thermochronometry (fission track and (U-Th)/He) to constrain the low temperature cooling history of the region. In the Hebridean Igneous Province denudation has removed much of the basaltic lava pile and has exposed the plutonic complexes emplaced at its base. This thermochronological investigation of these plutonic sequences shows that the initial cooling was very rapid. This is consistent with field evidence for shallow level emplacement, accompanied by extensive hydrothermal activity and syn-, and post-intrusive denudation. The new data from the zircon (U-Th)/He, apatite fission track, and apatite (U-Th)/He thermochronometers identifies a previously unresolved pulse of magnetic activity that occurred at approximately 47 Ma, significantly after the initiation of rifting, and the cessation of voluminous shallow level intrusion in the Hebridean Igneous Province. The timing of a short-lived low temperature event observed in the plutonic units on the islands of Rum (80 - 90°C peak temperature), and Skye (120 - 180°C peak temperature), correlates with a cooling episode of more than 200°C at the St Kilda Central Complex, 100 km further to the west.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:511204 |
| Date | January 2006 |
| Creators | Dobson, Katherine Joanna |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/4460/ |
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