View source for Permian volcanic activity, Midland Valley of Scotland

{{MVRG}}
== Permian volcanic activity  ==
Interbedded volcanic rocks of Permian age occur only in Ayrshire, where they form an annular outcrop around the overlying aeolian sandstones of the Mauchline Basin. Contemporaneous necks and sub-volcanic intrusions are abundant within and around the Mauchline lavas, and the late necks of east Fife and possibly East Lothian have late Stephanian to Lower Permian radiometric ages. Sills of various alkali dolerite rock-types are thought to be near contemporaneous with the Lower Permian lavas.

The Mauchline volcanic sequence, which increases in thickness eastwards from 100 to 238 m, rests unconformably but with no marked discordance upon Upper Coal Measures. Sediments resembling the overlying Mauchline Sandstones occur locally at the base of the sequence, as intercalations between flows and as infillings in slaggy flow tops. Lava flows are predominantly olivine-basalts of Dalmeny type, but some strongly silica-undersaturated basic types are characteristically present (nepheline-basanite, analcime-basanite, olivine-nephelinite) and analyses include some hypersthene-normative (transitional) basalts. Agglomerates and tuffs constitute a large part of the succession, becoming more abundant in the thicker, eastern parts.

Over 60 volcanic necks are known in Ayrshire, mostly within a 20 km radius of the Mauchline Basin, but also extending to West Kilbride in the north, Muirkirk in the east and Dalmellington in the south. Numerous lines of evidence suggest that these necks are contemporaneous with the Mauchline lavas and hence delimit the former extent of the volcanic field. Necks are known to cut the Coal Measures, post-Coal Measures alkali dolerite sills and the Mauchline lavas but not the Mauchline Sandstones. Those which cut older strata do so in areas where older volcanicity is not recorded. Many vents contain wind-rounded sand grains and some include large subsided blocks of Mauchline sandstone.

Vent agglomerates usually consist of a mixture of sedimentary and igneous material. Blocks and lapilli of Mauchline lava types are common and alkali dolerite, derived from sills, occurs locally. Plugs and other vent intrusions are predominantly of highly-undersaturated olivine-analcimite or monchiquite but alkali dolerite and camptonite are also known. Thin dykes and sills of monchiquite commonly occur in the vicinity of necks and monchiquite dykes are common in the Irvine valley and the Patna area. Many of the intrusions and agglomerates contain xenolithic megacrysts and nodules of carbonated peridotite.

== Bibliography ==
Black, G. P. 1966. Arthur’s Seat. A history of Edinburgh’s volcano. (Edinburgh: Oliver and Boyd.)

Chapman, N. A. 1976. Inclusions and megacrysts from undersaturated tuffs and basanites, east Fife, Scotland. J. Petrol., Vol. 17, pp. 472–498.

Craig, P. M. and Hall, I. H. S. 1975. The Lower Carboniferous rocks of the Campsie-Kilpatrick area. Scott. J. Geol., Vol. 11, pp. 171–174.

De Souza, H. A. F. 1974. Potassium-argon ages of Carboniferous igneous rocks from East Lothian and the south of Scotland. Unpublished M.Sc. thesis, University of Leeds.

De Souza, H. A. F. 1979. The geochronology of Scottish Carboniferous volcanism. Unpublished Ph.D. thesis, University of Edinburgh.

Fitch, F. J., Miller, J. A. and Williams, S. C. 1970. Isotopic ages of British Carboniferous rocks. C.R. 6e Congr. Int. Stratigr. Geol. Carbonif. (Sheffield, 1967), Vol. 2, pp. 771–789.

Forsyth, I. H. and Rundle, C. C. 1978. The age of the volcanic and hypabyssal rocks of east Fife. Bull. Geol. Surv. G.B., No. 60, pp. 23–29. Francis, E. H. 1978a. Igneous activity in a fractured craton: Carboniferous volcanism in northern Britain. In Bowes, D. R. and Leake, B. E. (editors). 1978. Crustal evolution in northwestern Britain and adjacent regions. Spec. Issue Geol. J., No. 10.

Forsyth, I. H. 1978b. The Midland Valley as a rift, seen in connection with the late Palaeozoic European Rift System. In Tectonics and Geophysics of Continental Rifts, pp. 133–147. Ramberg, I. B. and Neumann, E.-R. (editors). (Dordrecht: Reidel.)

Forsyth, I. H. 1982. Magma and sediment - 1. Emplacement mechanism of late Carboniferous tholeiite sills in northern Britain. J. Geol. Soc. London, Vol. 139, pp. 1–20.

Hall, J. 1974. A seismic reflection survey of the Clyde Plateau lavas in north Ayrshire and Renfrewshire. Scott. J. Geol., Vol. 9, pp. 253–279.

Johnstone, G. S. 1965. The volcanic rocks of the Misty Law-Knockside Hills district, Renfrewshire. Bull. Geol. Surv. G.B., No. 22, pp. 53–64.

Macdonald, J. G. and Whyte, F. 1981. Petrochemical evidence for the genesis of a Lower Carboniferous transitional basaltic suite in the Midland Valley of Scotland. Trans. R. Soc. Edinburgh: Earth Sci., Vol. 72, pp. 75–88.

Macdonald, R. 1975. Petrochemistry of the early Carboniferous (Dinantian) lavas of Scotland. Scott. J. Geol., Vol. 11, pp. 269–314.

Macdonald, R. 1980. Trace element evidence for mantle heterogeneity beneath the Scottish Midland Valley in the Carboniferous and Permian. Philos. Trans. R. Soc. London, Ser. A, Vol. 297, pp. 245–257.
Macdonald, R., Gottfried, D., Farrington, M. J., Brown, F. W. and Skinner, N. G. 1981. The geochemistry of a continental tholeiitic suite: late Palaeozoic quartz-dolerite dykes of Scotland. Trans. R. Soc. Edinburgh: Earth Sci., Vol. 72, pp. 57–74.

Macdonald, R., Thomas, J. E. and Rizzello, S. A. 1977. Variations in basalt chemistry with time in the Midland Valley province during the Carboniferous and Permian. Scott. J. Geol., Vol. 13, pp. 11–22.

Macgregor, A. G. 1928. The classification of Scottish Carboniferous olivine-basalts and mugearites. Trans. Geol. Soc. Glasgow, Vol. 18, pp. 324–360.

Macintyre, R. M., Cliff, R. A. and Chapman, N. A. 1981. Geochronological evidence for phased volcanic activity in Fife and Caithness necks, Scotland. Trans. R. Soc. Edinburgh: Earth Sci., Vol. 72, pp. 1–7.

Monro, S. K., Loughnan, F. C. and Walker, M. C. 1983. The Ayrshire bauxitic clay: an allochthonous deposit? In Residual Deposits, pp. 47–58. Wilson, R. C. L. (editor). Spec. Publ. Geol. Soc. London, No. 11.

Mykura, W. 1965. White trap in some Ayrshire coals. Scott. J. Geol., Vol. 1, pp. 176–184.

Mykura, W. 1967. The Upper Carboniferous rocks of south-west Ayrshire. Bull. Geol. Surv. G.B., No. 26, pp. 23–48.

Upton, B. G. J. (editor). 1969. Field excursion guide to the Carboniferous volcanic rocks of the Midland Valley of Scotland. (Edinburgh: Edinburgh Geological Society.)

Upton, B. G. J. 1982. Carboniferous to Permian volcanism in the stable foreland. In Sutherland, D. S. (editor). 1982. Igneous rocks of the British Isles.(Chichester: Wiley.)

Upton, B. G. J., Aspen, P. and Chapman, N. A. 1983. The upper mantle and deep crust beneath the British Isles: evidence from inclusions in volcanic rocks. J. Geol. Soc. London, Vol. 140, pp. 105–122.

Walker, F. 1935. The late Palaeozoic quartz-dolerites and tholeiites of Scotland. Mineral. Mag., Vol. 24, pp. 131–159.

Whyte, F. 1968. Lower Carboniferous volcanic vents in the west of Scotland. Bull. Volcanol., Vol. 32, pp. 253–268.

Whyte, F. and Macdonald, J. G. 1974. Lower Carboniferous vulcanicity in the northern part of the Clyde Plateau. Scott. J. Geol., Vol. 10, pp. 187–198. 


[[Category:Midland Valley of Scotland]]