Hostname: page-component-cd9895bd7-dk4vv Total loading time: 0 Render date: 2024-12-24T02:34:31.091Z Has data issue: false hasContentIssue false
  • English
  • Français

Early mafic magmatism and crustal anatexis on the Isle of Rum: evidence from the Am Màm intrusion breccia

Published online by Cambridge University Press:  25 March 2009

GRAEME R. NICOLL ,
MARIAN B. HOLNESS ,
VALENTIN R. TROLL ,
COLIN H. DONALDSON ,
EOGHAN P. HOLOHAN ,
C. HENRY EMELEUS  and
DAVID CHEW
GRAEME R. NICOLL*
Affiliation:
Department of Geology, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland
MARIAN B. HOLNESS
Affiliation:
Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK
VALENTIN R. TROLL
Affiliation:
Department of Geology, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland Department of Earth Sciences, Uppsala Universitet, Villavägen 16, 752 36 Uppsala, Sweden
COLIN H. DONALDSON
Affiliation:
School of Geosciences, University of St. Andrews, KY16 9AL, UK
EOGHAN P. HOLOHAN
Affiliation:
Department of Geology, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland School of Geological Sciences, University College Dublin, Dublin 4, Ireland
C. HENRY EMELEUS
Affiliation:
Department of Earth Sciences, University of Durham, Durham DHI 3LE, UK
DAVID CHEW
Affiliation:
Department of Geology, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland
*
†Author for correspondence: [email protected]; current address: School of GeoSciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3SW, UK.
Get access Rights & Permissions [Opens in a new window]

Abstract

The Rum Igneous Centre comprises two early marginal felsic complexes (the Northern Marginal Zone and the Southern Mountains Zone), along with the later central ultrabasic–basic layered intrusions. These marginal complexes represent the remnants of near-surface to eruptive felsic magmatism associated with caldera collapse, examples of which are rare in the North Atlantic Igneous Province. Rock units include intra-caldera collapse breccias, rhyolitic ignimbrite deposits and shallow-level felsic intrusions, as well the enigmatic ‘Am Màm intrusion breccia’. The latter comprises a dacitic matrix enclosing lobate basaltic inclusions (~1–15 cm) and a variety of clasts, ranging from millimetres to tens of metres in diameter. These clasts comprise Lewisian gneiss, Torridonian sandstone and coarse gabbro. Detailed re-mapping of the Am Màm intrusion breccia has shown its timing of emplacement as syn-caldera, rather than pre-caldera as previously thought. Textural analysis of entrained clasts and adjacent, uplifted country rocks has revealed their thermal metamorphism by early mafic intrusions at greater depth than their present structural position. These findings provide a window into the evolution of the early mafic magmas responsible for driving felsic magmatism on Rum. Our data help constrain some of the physical parameters of this early magma–crust interaction and place it within the geochemical evolution of the Rum Centre.

Keywords

North Atlantic Igneous ProvinceIsle of Rumfelsic magmasintrusion brecciageochemistrymagma–crust interaction
Type
Original Article
Information
Geological Magazine , Volume 146 , Issue 3 , May 2009 , pp. 368 - 381
Copyright
Copyright © Cambridge University Press 2009

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Bailey, E. B. 1945. Tertiary igneous tectonics of Rhum (Inner Hebrides). Quarterly Journal of the Geological Society of London 100, 165–91.Google Scholar
Black, G. P. 1954. The acid rocks of western Rhum. Geological Magazine 91, 257–72.CrossRefGoogle Scholar
Brown, D. J., Holohan, E. P. & Bell, B. R. 2009. Sedimentary and volcano-tectonic processes in the British Paleocene Igneous Province: a review. Geological Magazine 146, 326–52.CrossRefGoogle Scholar
Chambers, L. M., Pringle, M. S. & Parrish, R. R. 2005. Rapid formation of the Small Isles Tertiary centre constrained by precise 40Ar/39Ar and U–Pb ages. Lithos 79, 367–84.CrossRefGoogle Scholar
Chew, D. M., Graham, J. R. & Whitehouse, M. J. 2007. U–Pb zircon geochronology of plagiogranites from the Lough Nafooey (= Midland Valley) arc in western Ireland: constraints on the onset of the Grampian orogeny. Journal of the Geological Society, London 164, 747–50.CrossRefGoogle Scholar
Dingwell, D. B. & Webb, S. L. 1989. Structural relaxation in silicate melts and non-Newtonian melt rheology in geologic processes. Physics and Chemistry of Minerals 16, 508–16.Google Scholar
Dunham, A. C. 1968. The felsites, granophyre, explosion breccias and tuffisites of the north eastern margin of the Tertiary igneous complex of Rhum, Inverness-shire. Quarterly Journal of the Geological Society of London 123, 327–52.Google Scholar
Dunham, A. C. & Thompson, R. N. 1967. The origin of granitic magma: Skye and Rhum. Journal of the Geological Society of Australia 14, 339–44.CrossRefGoogle Scholar
Emeleus, C. H. 1985. The Tertiary lavas and sediments of northwest Rhum, Inner Hebrides. Geological Magazine 122, 419–37.Google Scholar
Emeleus, C. H. 1997. Geology of Rum and the adjacent islands. Memoirs of the British Geological Survey Sheet 60, (Scotland).Google Scholar
Emeleus, C. H., Wadsworth, W. J. & Smith, N. J. 1985. The early igneous and tectonic history of the Rhum Tertiary Volcanic Centre. Geological Magazine 122, 451–7.Google Scholar
Garner, A. & McPhie, J. 1999. Partially melted lithic megablocks in the Yardea Dacite, Gawler Range Volcanics, Australia: implications for eruption and emplacement mechanisms. Bulletin of Volcanology 61, 396–410.CrossRefGoogle Scholar
Harker, A. 1908. The geology of the Small Isles of Inverness shire. Memoirs of the Geological Survey, Scotland, Sheet 60, 210 pp.Google Scholar
Holness, M. B. 2005. Spatial constraints on magma chamber replenishment events from textural observations of cumulates: the Rum Layered Intrusion, Scotland. Journal of Petrology 46, 1585–1601.CrossRefGoogle Scholar
Holness, M. B., Cheadle, M. J. & McKenzie, D. P. 2005. On the use of changes in dihedral angle to decode late-stage textural evolution in cumulates. Journal of Petrology 46, 1565–83.CrossRefGoogle Scholar
Holness, M. B. & Isherwood, C. E. 2003. The aureole of the Rum Tertiary Igneous Complex, Scotland. Journal of the Geological Society, London 160, 15–27.CrossRefGoogle Scholar
Holness, M. B. & Sawyer, E. W. 2008. On the pseudomorphing of melt-filled pores in migmatites. Journal of Petrology 49, 1343–63.Google Scholar
Holness, M. B., Tegner, C., Nielsen, T. F. D., Stripp, G. & Morse, S. A. 2007. A textural record of solidification and cooling in the Skaergaard Intrusion, East Greenland. Journal of Petrology 48, 2539–77.CrossRefGoogle Scholar
Holohan, E. P., Troll, V. R., Errington, M., Donaldson, C. H., Nicoll, G. R. & Emeleus, C. H. 2009. The Southern Mountains Zone, Isle of Rum, Scotland: volcanic and sedimentary processes upon an uplifted and subsided magma chamber roof. Geological Magazine 146, 400–18.CrossRefGoogle Scholar
Hughes, C. J. 1960. The Southern Mountains Igneous Complex, Isle of Rhum. Quarterly Journal of the Geological Society of London 116, 111–38.CrossRefGoogle Scholar
Kennedy, B. M., Jellinek, M. J. & Stix, J. 2008. Coupled caldera subsidence and stirring inferred from analogue models. Nature Geoscience 1, 385–9.Google Scholar
Larsen, R. H. & Tegner, C. 2006. Pressure conditions for the solidification of the Skaergaard intrusion: eruption of East Greenland flood basalts in less than 300,000 years. Lithos 92, 181–97.Google Scholar
Meyer, R., Nicoll, G. R., Hertogen, J., Troll, V. R., Ellam, R. M. & Emeleus, C. H. 2009. Trace element and isotope constraints on crustal anatexis by upwelling mantle melts in the North Atlantic Igneous Province: an example from the Isle of Rum, NW Scotland. Geological Magazine 146, 382–99.Google Scholar
Nielsen, T. F. D. 2004. The shape and volume of the Skaergaard Intrusion, East Greenland: implications for mass balance and bulk composition. Journal of Petrology 45, 507–30.Google Scholar
Pinkerton, H. & Stevenson, R. J. 1992. Methods of determining the rheological properties of magmas at sub-liquidus temperatures. Journal of Volcanology and Geothermal Research 53, 47–66.Google Scholar
Thompson, R. N. 1981. Thermal aspects of the origin of Hebridean Tertiary acid magmas. I. An experimental study of partial fusion of Lewisian gneisses and Torridonian sediments. Mineralogical Magazine 44, 161–70.CrossRefGoogle Scholar
Troll, V. R., Donaldson, C. H. & Emeleus, C. H. 2004. Pre-eruptive magma mixing in ash-flow deposits of the Tertiary Rum igneous centre, Scotland. Contributions to Mineralogy and Petrology 147, 722–39.Google Scholar
Troll, V. R., Emeleus, C. H. & Donaldson, C. H. 2000. Caldera formation in the Rum Central Igneous Complex, Scotland. Bulletin of Volcanology 62, 301–17.Google Scholar
Troll, V. R., Nicoll, G. R., Emeleus, C. H. & Donaldson, C. H. 2008. Dating the onset of volcanism at the Rum Igneous Centre, NW Scotland. Journal of the Geological Society 165, 651–9.Google Scholar
Upton, B. G. J., McClurg, J., Skovgaard, A. C., Kirstein, L., Cheadle, M., Emeleus, C. H., Wadsworth, W. J. & Fallick, A. E. 2002. Picritic magmas and the Rum ultramafic complex, Scotland. Geological Magazine 139, 437–52.Google Scholar
Wager, L. R. & Brown, G. M. 1951. A note on rhythmic layering in the ultrabasic rocks of Rhum. Geological Magazine 88, 166–8.Google Scholar
Wager, L. R. & Brown, G. M. 1968. Layered igneous rocks. Edinburgh: Oliver and Boyd, 588 pp.Google Scholar
Walsh, J. N., Beckinsale, R. D., Skelhorm, R. R. & Thorpe, R. S. 1979. Geochemistry and petrogenesis of Tertiary granitic rocks from the Islend of Mull, northwest Scotland. Contributions to Mineralogy and Petrology 71, 99–116.CrossRefGoogle Scholar
Williams, P. J. 1985. Pyroclastic rocks in the Cnapan Breaca felsite, Rhum. Geological Magazine 122, 447–50.Google Scholar