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Igneous stratigraphy and internal structure of the Little Minch Sill Complex, Trotternish Peninsula, northern Skye, Scotland

  • Sally A. Gibson (a1) and Adrian P. Jones (a1)

Detailed sampling of the Little Minch Sill Complex reveals that it is composed of both single and multiple sills. These are formed of three main, genetically related units: picrite, picrodolerite and crinanite, which are the result of differentiation of an alkali-olivine basalt magma (approximately 10% MgO) in an upper-crustal magma chamber. Variations in igneous stratigraphy and the presence of internal chills in the Trotternish sills suggest that they were emplaced by multiple intrusion and subsequently differentiated in situ. Changes in petrography adjacent to pegmatite veins and textures within picrite units indicate compaction and filter-pressing were important processes after emplacement. Rhythmic layering (1 cm to 1 m thick) is conspicuous in the sills near contacts but does not involve cryptic mineral variation. Such modal layering may be more common than realised in relatively small-scale intrusions and maybe modelled in terms of in situ differentiation under conditions of significant undercooling in a changing thermal gradient at the synthetic for-sterite-diopside-anorthite eutectic.

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Anderson F. W. & Dunham K. C. 1966. The Geology of Northern Skye. Memoirs of the Geological Survey.
Barriere M. 1976. Flowage differentiation: limitation of the ‘Bagnold effect’ to narrow intrusions. Contributions to Mineralogy andPetrology 55, 139–45.
Bell B. R. & Harris J. W. 1986. An Excursion Guide to the Geology of the Isle of Skye. Geological Society of Glasgow.
Blake S. & Ivey G. I. 1986. Density and viscosity gradients in zoned magma chambers, and their influence on withdrawal dynamics. Journal of Volcanology and Geothermal Research 30, 201–30.
Brown G. M. 1969. The Tertiary Igneous Geology of the Isle of Skye. Geologists' Association Guide No. 13.
Bryan W. B., Finger L. W. & Chayes F. 1969. Estimating proportions in petrographic mixing equations by least squares approximation. Science 163, 1926–7.
Basaltic Volcanism Study Project (BVSP). 1981. Basalt Volcanism on the Terrestrial Planets. Pergamon.
Carmichael I. S. E., Turner F. J. & Verhoogen J. 1974. Igneous Petrology. New York: McGraw-Hill.
Chesher J. A., Smythe D. K. & BISHOP P. 1983. The Geology of the Minches, Inner Sound and Raasay. Institute of Geological Sciences Report, 83/6.
Donaldson C. H. 1976. An experimental investigation of olivine morphology. Contributions to Mineralogy and Petrology 57, 187213.
Drever H. I. 1953. A note on the field relations of the Shiant Isles picrite. Geological Magazine 90, 159–60.
Drever H. I. & Johnston R. 1957. A note on the occurrence of rhythmic layering in the Eilean Mhuire sill, Shiant Isles. Geological Magazine 94, 277–80.
Drever H. I. & Johnston R. 1959. The lower margin of the Shiant Isles sill. Quarterly Journal of the Geological Society of London 94, 343–65.
Drever H. I. & Johnston R. 1965. New petrographical data on the Shiant Isles picrite. Mineralogical Magazine 34, 194203.
Drever H. I. & Johnston R. 1967. The ultrabasic facies in some sheets and sills. In Ultramafic and Related Rocks (ed. Wyllie P. J.), pp. 5163. New York: Wiley.
Dunham A. C. 1965. A new type of banding in ultrabasic rocks from central Rhum, Inverness-shire Scotland. American Mineralogist 50, 1410–20.
Frey F. A., Green D. H. & Roy S. D. 1978. Integrated models of basalt petrogenesis: a study of quartz tholeiites to olivine melilitites from South Australia utilizing geochemical and experimental petrological data. Journal of Petrology 19, 463513.
Gibb F. G. F. 1973. The zoned clinopyroxenes of the Shiant Isles sill, Scotland. Journal of Petrology 14, 203–30
Gibb F. G. F. & Gibson S. A. 1989. The Little Minch Sill Complex. Scottish Journal of Geology 25, 367–70.
Gibb F. G. F. & Henderson C. M. B. 1984. The structure of the Shiant Isles sill complex, Outer Hebrides. Scottish Journal of Geology 20, 21–9.
Gibb F. G. F. & Henderson C. M. B. 1989. Discontinuities between picritic and crinanitic units in the Shiant Isles sill: evidence of multiple intrusion. Geological Magazine 126, 127–37.
Gibson S. A. 1990. The geochemistry of the Trotternish sills, Skye, Scotland: crustal contamination in the British Tertiary Volcanic Province. Journal of the Geological Society, London 147, 1071–81.
Huppert H. E. & Sparks R. S. J. 1989. Chilled margins in igneous rocks. Earth and Planetary Science Letters 92, 397405.
Murray R. J. 1954. The clinopyroxenes of the Garbh Eilean sill, Shiant Isles. Geological Magazine 91, 1731.
Murata K. J. & Richter D. H. 1976. The 1959–1960 eruptions of Kilauea volcano, Hawaii; chemistry of the lavas. U.S. Geological Survey Professional Paper 537A, 126.
Nash W. P. & Wilkinson J. F. G. 1970. Shonkin Sag Laccolith, Montana. 1. Mafic minerals and estimates of temperature, pressure, oxygen fugacity and silica-activity. Contributions to Mineralogy and Petrology 25, 241–69.
Roeder P. L. & Emslie R. F. 1970. Olivine-liquid equilibrium. Contributions to Mineralogy and Petrology 29, 275–89.
Simkin T. 1967. Flow differentiation in the picritic sills of north Skye. In Ultramific and Related Rocks (ed. Wyllie P. J.), pp.64. New York: Wiley.
Sparks R. S. J., Huppert H. E., Kerr R. C., McKenzie D. P. & Tait S. R. 1985. Postcumulus processes in layered intrusions. Geological Magazine 122, 555–68
Wager L. R. & Brown G. M. 1967. Layered Igneous Rocks. Edinburgh: Oliver & Boyd.
Walker F. 1930. The geology of the Shiant Isles (Hebrides). Quarterly Journal of the Geological Society, London 86, 355–98.
Walker F. 1931. The dolerite isles of the North Minch. Transactions of the Royal Society of Edinburgh 56, 753–66.
Walker F. 1932. Differentiated sills of Northern Trotternish (Skye). Transactions of the Royal Society of Edinburgh 57, 241–57.
Wilkinson J. F. G. 1957. The clinopyroxenes of a differentiated sill near Guennedah, New South Wales. Geological Magazine 94, 123–34.
Young I. M. & Donaldson C. H. 1985. Formation of granular layers within the Rhum crystal pile. Geological Magazine 122, 519–28.
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