This article explores a CD-based courseware package for the teaching and consolidating of geological field skills used for the interpretation of folding sequences in deformed rocks, focussing on examples from Anglesey in North Wales. The article briefly considers the advantages and disadvantages of virtual fieldwork and then discusses the rationale, structure, development and production of the CD courseware package.
This article explores a CD-based courseware package for the teaching and consolidating of geological field skills used for the interpretation of folding sequences in deformed rocks, focusing on examples from Anglesey in North Wales. The article briefly considers the advantages and disadvantages of virtual field work and then discusses the rationale, structure, development and production of the CD-ROM courseware package.
Abstract A steeply dipping set of quartz-chlorite-muscovite-biotite veins was emplaced, at depths of at least 14 km and temperatures >400°C, into Môna Complex metasedimentary rocks of Holy Island, after the D4 event. Vein trends range from northeast-southwest to north-northwest-south-southeast. Vein offshoots, consistently oriented c. 10–35° anticlockwise relative to the main vein, are common. Quartz fibres within different veins show a range of orientations, from northwest-southeast to east-west, and are interpreted as tracking vein opening directions. Vein and fibre orientations are integrated into a four-stage model for vein emplacement. At each stage, new main veins either open extensionally, with fibres subnormal to their boundaries, or by hybrid extension-shear. Hybrid main veins commonly have extensional offsoots. Extensional main veins are orientated progressively further anticlockwise with time from a dominantly northeast-southwest trend to a dominantly north-south trend, but hybrid main veins have out-of-sequence orientations and probably utilized pre-existing fractures. The dominance of extensional and hybrid extension-shear vein opening indicates that the differential stress was small and pore fluid pressure was high. A study of length-thickness relationships has revealed that this vein set is self-affine with vein widening progressing more quickly than elongation during growth. Linear transect analyses show that the vein spacings have fractal characteristics.
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