The emplacement processes of the Whin Sill complex and its associated dykes have been studied using a combined approach of detailed field and magnetic investigations. Regional palaeodirectionai results show two different but consistent palaeomagnetic signatures and allow the sill complex to be subdivided into three geographically separate intrusions: the 'Holy Island Sill', the 'Alnwick Sill' and the ' Hadrian's Wall-Pennine Sill', The Little Whin Sill has been identified previously as a fourth, separate sill on petrological evidence. On the basis of the palaeodirectional results it is also possible to relate the exposed contemporaneous dykes to the individual intrusions. The magma flow geometries within the individual Whin Sill intrusions were detennined by AMS analyses, and both traditional and newly identified magma flow indicators. For the Holy Island Sill the results suggest that the magma flow was homogeneously southwards directed and that the Holy Island Dyke acted as the feeder to this intrusion. In the Alnwick Sill the magma flow was homogeneously westwards directed and it is proposeU that an offshore, en echelon segment of the High Green Dyke fed the Alnwick Sill. The magma flow geometry for the Hadrian's Wall-Pennine Sill is complex. The results suggest that this intrusion was fed by the Hett Dyke and that the magma flow within the sill was generally north and north westwards directed. It is proposed that the intrusion was emplaced during a phase of late Variscan, E-W compression and that pre-existing faults at a high angle to this compression direction acted as a magma flow barrier along which the magma became deflected. The geometry of the sills is approximately that of a quarter- to half-saucer-shape, with the dykes being situated at the saucer truncation. From the feeder dykes magma was injected into the individual sill bodies and the magma flow was generally up dip or parallel to the strike of the host rock bedding, thus out of the basin centres and into levels of lower lithospheric pressure. It is proposed that a compressional stress field and locally overpressured horizons had a significant impact on the initiation and emplacement of the Whin Sill complex.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:403441 |
| Date | January 2003 |
| Creators | Liss, Dirk |
| Publisher | University of Birmingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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