Caledonian magmatism, Grampian Highlands

From: Stephenson, D, and Gould, D. 1995. British regional geology: Grampian Highlands. Fourth edition. Keyworth, Nottingham: British Geological Survey.

Caledonian magmatism, introduction

In the discussion which follows, the established divisions of Older, Syntectonic and Newer Igneous Rocks used in the third edition of this handbook have largely been modified, to become a seven-fold division of the Caledonian Igneous Suite. Each division or grouping is linked to one or more episodes in the history of deformation events in the development of the Caledonian Orogen, which spanned the period from about 750 to 390 Ma. Excluding the events recorded by the tectonically emplaced Highland Border Complex (Chapter 9), the principal magmatic episodes were as follows:

1. Pre-tectonic basic magmatism† (magmatism predates the Caledonian Orogeny as currently defined)

2. Syntectonic granitic intrusions^† (magmatism predates the Caledonian Orogeny as currently defined])

3. Syn- to late-tectonic basic and ultramafic intrusions

4. Late-tectonic granitoid intrusions

5. Post-tectonic granitoid intrusions

6. Late- to post-tectonic minor intrusions

7. Lower Old Red Sandstone volcanism

The distribution of components of these groups, except for the minor intrusions, is shown on P915434; each is numbered and referenced in italics in the text, e.g. Dunfallandy Hill Granite (8).

The age of an intrusion with respect to the tectonic history of the surrounding rocks cannot always be determined from the local field evidence, especially in areas of poor exposure, and hence certain intrusions have been assigned to a suite by analogy with petrologically similar intrusions whose structural setting is better known. It should be noted also that the three latest suites were largely contemporaneous.