Geological processes in the British Isles
Geological processes in the British Isles

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Geological processes in the British Isles

7 Course questions

Now you have completed this course, try the following questions to test your understanding of this material.

Question 19

Like the Variscan Orogenic Belt, the Caledonian includes large granitic intrusions. Using the Ten Mile Maps in conjunction with Figure 9, determine whether these intrusions are confined to specific geographical regions, to the high-grade metamorphic Caledonides, or to the low-grade to non-metamorphic Caledonides.

Answer

Examination of the Ten Mile Map (N) shows that large granitic intrusions (34) occur in both high-grade metamorphic and low-grade to non-metamorphic parts of the Caledonides in Scotland and northern England, but are absent in Wales.

Question 20

On Figure 11, the boundary between the Variscan Orogenic Belt and the Older Cover in southern Wales is shown. From the fold structures on the Ten Mile Map (S), can you pinpoint this line or is the boundary between the two lithotectonic units more subtle?

Answer

Although the boundary is shown as a distinct dotted line on Figure 11, it is not possible to use the outcrop patterns to locate this boundary precisely on the Ten Mile Map.

In south-west England, the Variscan is characterised by relatively intense E–W folding (the intensity of which is not apparent on the Ten Mile Map), forming a complex syncline. In the Mendips (ST(31)4050 just south of Bristol) and southern Wales, a series of asymmetrical folds can be seen on the Ten Mile Map. These intense folds trend E–W in the Mendips, but WNW–ESE in southern Wales. The more open syncline of the south Wales Carboniferous coalfields may be associated with the Variscan folding, but is not included in the orogenic belt on Figure 11. To the north of Bristol (ST(31)5070), the fold axes have swung round to a N–S orientation, and are therefore obviously different to the Variscan trend.

Therefore, the tectonic distinction between the Variscan and Older Cover lithotectonic units does not form a sharp well-defined line, but is gradational in nature.

Question 21

Using the contour lines in Figure 9, describe how the thickness of the Younger Cover varies between onshore and offshore areas.

Answer

Figure 9 shows that the onshore Younger Cover areas are much thinner (generally <1 km) than the offshore areas (which are up to 6 km thick).

We hope you have enjoyed this course and that it has given you a satisfactory taste of the really rather splendid, if intricate, geological history of the British Isles. We hope too that you have an appreciation of the complexities of some of the evidence upon which the geological history of the British Isles as presented in this course is based.

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