Caledonian magmatism, Grampian Highlands

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Stephenson, D, and Gould, D. 1995. British regional geology: the Grampian Highlands. Fourth edition. Reprint 2007. Keyworth, Nottingham: British Geological Survey.

Caledonian magmatism, introduction[edit]

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 above articles, 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.

On P915434 Name Age (Ma) Type 87Sr/86Sri Geochronological reference
Pre-tectonic basic magmatism
2 Tayvallich 595 ± 4 U/Pb Zr Halliday et al., 1989
Syntectonic granitic intrusions
6 Ben Vuirich 590 ± 2 U/Pb Zr Rogers et al., 1989
8 Dunfallandy Hill 481 ± 15 Rb/Sr WRI 0.7185 ± 0.0008 Pankhurst and Pidgeon, 1976
9 Glen Clova (Rough Craig) 549 ± 44 Rb/Sr WR 0.7166 ± 0.0024 Robertson, 1994
Syn- to late-tectonic basic and ultramafic intrusions
14 Insch 489 ± 17 Rb/Sr WRI 0.7117 ± 0.0003 Pankhurst, 1970
23 Huntly 476 ± 5 K/Ar Bi Brown et al., 1965
27 Haddo House 491 ± 6 K/Ar Bi Brown et al., 1965
Late-tectonic granitoid intrusions
(i) North-eastern biotite-muscovite-granites
26 Belhelvie pegmatites 472 ± 5 Rb/Sr WRI 0.7185 ± 0.0016 van Breemen and Boyd, 1972
36 Kemnay 411 ± 7 Rb/Sr Mins 0.715 ± 0.002 Bell, 1968
37 Aberdeen 470 ± 1 U/Pb Mon Kneller and Aftalion, 1987
38 Auchlee 439 ± 7 Rb/Sr Mins 0.733 ± 0.004 Bell, 1968
40 Strichen 475 ± 5 U/Pb Mon Pidgeon and Aftalion, 1978
455 ± 22 Rb/Sr WRI 0.7172 ± 0.0011 Pankhurst, 1974
42 Aberchirder 444 ± 9 Rb/Sr WRI 0.7157 ± 0.0008 Pankhurst, 1974
43 Longmanhill 470 ± 50 Rb/Sr WRI Pankhurst, 1974
(ii) North-western biotite-muscovite-granites
46 Ardclach 475 ± 7 U/Pb Mon Zaleski, 1983
47 Moy (main phase) 455 + 27/ -15 Rb/Sr WR + U/Pb Mon 0.7185 ± 0.0001 Zaleski, 1983
49 Glen Kyllachy 443 + 5/-15Rb/Sr WR/Bi 0.7176 ± 0.0004 van Breemen and Piasecki, 1983
50 Maol Chnoc 436 ± 8 Rb/Sr Mins 0.717 Clayburn, 1981
51 Strathspey 437 ± 16 K/Ar Bi Miller and Brown, 1965
52 Loch Laggan 439 ± 7 Rb/Sr Mins 0.705 - 0.718 Clayburn, 1981
(iii) North-eastern diorites to granodiorites
53 Kennethmont 453 ± 4 Rb/Sr WRI 0.7145 ± 0.0013 Pankhurst, 1974
Post-tectonic granitoid intrusions
(i) South Grampian Suite
56 Garabal Hill–Glen Fyne 406 ± 41 Rb/Sr WRMI 0.705 ± 0.003 Summerhayes, 1966
Garabal Hill–Glen Fyne 429 ± 22 U/Pb Zr Rogers and Dunning, 1991
57 Arrochar 426 ± 33 U/Pb Sph Rogers and Dunning, 1991
65 Comrie 408 ± 5 Rb/Sr WRMI 0.705 - 0.707 Turnell, 1985
Rubha Mor (Appinite pipe) 427 ± 3 U/Pb Sph Rogers and Dunning, 1991
(ii) Argyll Suite
66 Moor of Rannoch 408 ± 18 K/Ar Bi; Rb/Sr WRMI 0.7048 Miller and Brown, 1965; Clayburn, 1981
67 Strath Ossian 405 ± 9 Rb/Sr WRMI 0.7059 Clayburn, 1981
400 ± 10 U/Pb Zr Pidgeon and Aftalion, 1978
68 Ballachulish 406 ± 34 Rb/Sr WRI 0.7040 ± 0.0002 Haslam and Kimbell, 1981
72 Etive 401 ± 64 Rb/Sr WRI 0.7058 ± 0.0004 Clayburn et al., 1983
396 ± 125 Rb/Sr WRI 0.7055 ± 0.0005 Clayburn et al., 1983
74 Foyers c.415 various Pankhurst, 1979
405 ± 86 Rb/Sr WRMI c. 0.707 Clayburn, 1981
403 ± 97 Rb/Sr WRMI c. 0.7045 Clayburn, 1981
75 Findhorn 413 ± 5 Rb/Sr WRMI c. 0.706 van Breemen and Piasecki, 1983
77 Corrieyairack 434 ± 9 Rb/Sr WRMI 0.7056 Clayburn, 1981
78 Allt Crom c. 405 Rb/Sr WR 0.7056 Clayburn, 1981
81 Crathes 420 ± 2 K/Ar Bi Brown et al., 1965
(iii) Cairngorm Suite
87 Moy (Saddle Hill) 407 ± 5 Rb/Sr WRI 0.7081 ± 0.0002 Zaleski, 1983
90 Ben Rinnes 411 ± 3 Rb/Sr WRI 0.7072 ± 0.0020 Zaleski, 1985
93 Monadhliath 419 ± 5 Rb/Sr WRI 0.7058 ± 0.0008 Harrison and Hutchinson, 1987
94 Cairngorm 408 ± 3 Rb/Sr WRI 0.7062 ± 0.0004 Harmon et al., 1984
95 Lochnagar 415 ± 5 Rb/Sr WRI 0.7065 ± 0.0002 Halliday et al., 1979
96 Glen Gairn 404 ± 6 Rb/Sr WRI 0.7081 ± 0.0015 Harrison and Hutchinson, 1987
98 Mount Battock 416 ± 4 Rb/Sr WRI 0.7058 ± 0.0004 Harrison and Hutchinson, 1987
102 Hill of Fare 413 ± 3 Rb/Sr WRI 0.7057 ± 0.0003 Halliday et al., 1979
103 Bennachie 400 ± 4 Rb/Sr WRI 0.7062 ± 0.0004 Darbyshire and Beer, 1988
104 Middleton 398 ± 19 Rb/Sr WR 0.7092 ± 0.0181 Darbyshire and Beer, 1988
105 Peterhead 406 ± 13 volcanic rock Rb/Sr Mins Bell, 1968
Lower Old Red Sandstone volcanic rocks
108 Lorn Plateau 400 ± 5 Rb/Sr WRI 0.7047 Clayburn et al., 1983
421 - 413 Ar degassing Thirlwall, 1988
NB All Rb/Sr and K/Ar ages recalculated using the decay constants of Steiger and Jaeger, 1977. WR = Whole rock (no isochron) WRI = Whole rock isochron WRMI = Whole rock – mineral isochron Mins = Mineral age (no isochron) Bi = Biotite Zr = Zircon Mon = Monazite Sph = Sphene
1 Average for complex 2 Appinitic diorite 3 Appinite 4 Meall Odhar Granite 5 Central Starav Granite 6 Tonalite and granodiorite 7 Granite.

Full list of references[edit]