There are a number of geochemically, geographically and, in most cases, stratigraphically distinct magma types around the igneous centres of Tayvallich and Loch Awe which represent separate phases of magmatism. These have been characterised by trace element geochemistry. Relationships have been established between some of the magmas, however the full range of rocks in the area (from alkaline to tholeiitic) cannot be accounted for by melting or fractional crystallisation processes, implying more than one melt source for the igneous activity. Extension across the area produced a number of parallel basins, but movement along the Cruachan Lineament allowed rotational opening of the Loch Awe basin which became a major volcanic centre. During this period, the centre of igneous activity moved in successive stages from the Tayvallich Peninsula to the Loch Awe area, producing a series of magmas, ranging from alkaline to transitional and tholeiitic. The data confirm a general increase in melt fraction and a source which was being gradually modified. A similar series can be seen on Islay and Jura. There is a strong correlation between different magma types and individual basins and sub-basins, from which we conclude that the magmatism was controlled by basin formation and evolution. The igneous activity was therefore passive and was driven by the extensional tectonics prevailing at that time. The relationship between the Green Beds and the Loch Avich Volcanics has been re-assessed. The igneous component in the Green Beds is derived from erosion of Loch Awe lavas, and the younger Loch Avich Lavas represent a final, minor episode of igneous activity. Their anomalous geochemistry is due to contamination of the small volume melt prior to eruption.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:652628 |
| Date | January 2006 |
| Creators | Howard, Martin |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/10964 |
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