Hostname: page-component-848d4c4894-m9kch Total loading time: 0 Render date: 2024-05-14T23:38:15.847Z Has data issue: false hasContentIssue false
  • English
  • Français

Palaeomagnetic and anisotropy of magnetic susceptibility data bearing on the emplacement of the Western Granite, Isle of Rum, NW Scotland

Published online by Cambridge University Press:  11 December 2008

M. S. PETRONIS ,
B. O'DRISCOLL ,
V. R. TROLL ,
C. H. EMELEUS  and
J. W. GEISSMAN
M. S. PETRONIS*
Affiliation:
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA
B. O'DRISCOLL*
Affiliation:
Department of Geology, Museum Building, Trinity College, Dublin 2, Ireland
V. R. TROLL
Affiliation:
Department of Geology, Museum Building, Trinity College, Dublin 2, Ireland
C. H. EMELEUS
Affiliation:
Department of Earth Sciences, University of Durham, Science Laboratories, South Road, Durham, DHI 3 LE, UK
J. W. GEISSMAN
Affiliation:
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA
*
†Author for correspondence: mspetro@nmhu.edu; now at Environmental Geology, Natural Resource Management Department, New Mexico Highlands University, P.O. Box 9000, Las Vegas, NM 87701, USA
§School of Physical and Geographical Sciences, Keele University, Keele ST5 5BG, UK
Get access Rights & Permissions [Opens in a new window]

Abstract

The Western Granite is the largest of several granitic bodies around the margin of the Rum Central Igneous Complex. We report palaeomagnetic and anisotropy of magnetic susceptibility (AMS) data that bear on the emplacement and deformation of the Western Granite. The collection includes samples from 27 sites throughout the Western Granite, five sites in adjacent feldspathic peridotite, and two sites in intermediate to mafic hybrid contact aureole rocks. Palaeomagnetic data from 22 of the 27 sites in the granite provide an in situ group mean D = 213.2°, I = −69.5°, α95 = 5.5° that is discordant to an early Paleocene reverse polarity expected field (about 184°, −66°, α95 = 4.3°). The discrepancy is eliminated by removing an inferred 15° of northwest-side-down tilting about a best fit horizontal tilt axis trending 040°. Data from the younger peridotite and hybrid rocks of the Rum Layered Suite provide an in situ group mean of D = 182.6°, I = −64.8°, α95 = 4.0°, which is statistically indistinguishable from an early Paleocene expected field, and imply no post-emplacement tilting of these rocks since remanence acquisition. The inferred tilt recorded in the Western Granite, which did not affect the younger Layered Suite, suggests that emplacement of the ultrabasic rocks resulted in roof uplift and associated tilt of the Western Granite to make space for mafic magma emplacement. Magnetic fabric magnitude and susceptibility parameters yield two subtle groupings in the Western Granite AMS data set. Group 1 data, defined by rocks from exposures to the east and south, have comparatively high bulk susceptibilities (Kmean, 29.51 × 10−3 in SI system), stronger anisotropies (Pj, 1.031) and oblate susceptibility ellipsoids. Group 2 data, from rocks in the west part of the pluton, have lower values of Kmean (15.89 × 10−3 SI) and Pj (1.014), and triaxial susceptibility ellipsoids. Magnetic lineations argue for emplacement of the granite as a tabular sheet from the south–southeast toward the north and west. Moderate to steeply outward-dipping magnetic foliations, together with deflection of the country rock bedding in the north, are consistent with doming accompanying magma emplacement.

Keywords

palaeomagnetismanisotropy of magnetic susceptibilitymagma emplacementIsle of Rumgranite
Type
Original Article
Information
Geological Magazine , Volume 146 , Issue 3 , May 2009 , pp. 419 - 436
Copyright
Copyright © Cambridge University Press 2008

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.CrossRefGoogle Scholar
Bailey, E. B., Clough, C. T., Wright, W. B., Richey, J. E. & Wilson, G. V. 1924. Tertiary and Post-Tertiary geology of Mull, Loch Aline and Oban. Memoir of the Geological Survey of Great Britain, Sheet 44, Scotland, 445 pp.Google Scholar
Balsley, J. R. & Buddington, A. F. 1958. Iron titanium oxide minerals, rocks, and aeromagnetic anomalies of the Adirondack area, New York. Economic Geology 53 (7), 777–805.CrossRefGoogle Scholar
Beck, M. E. 1980. Palaeomagnetic record of plate-margin tectonic processes along the western edge of North America. Journal of Geophysical Research 85, 7115–31.CrossRefGoogle Scholar
Bell, J. D. 1979. Granites and associated rocks of the eastern part of the Western Redhills Complex, Isle of Skye. Transactions of the Royal Society of Edinburgh 66, 307–43.CrossRefGoogle Scholar
Besse, J. & Courtillot, V. 2002. Apparent and true polar wander and the geometry of the geomagnetic field over the last 200 Myr vol 107, art no 2300, 2002. Journal of Geophysical Research–Solid Earth 108, 2469.Google Scholar
Black, G. P. 1952. The age relationship of the granophyre and basalt of Orval, Isle of Rhum. Geological Magazine 89, 106–12.CrossRefGoogle Scholar
Black, G. P. 1954. The acid rocks of western Rhum. Geological Magazine 91, 257–72.CrossRefGoogle Scholar
Blake, D. H., Elwell, R. W. D., Gibson, I. L., Skelhorn, R. R. & Walker, G. P. L. 1965. Some relationships resulting from the intimate association of acid and basic magmas. Quarterly Journal of the Geological Society of London 121, 31–49.CrossRefGoogle Scholar
Bouchez, J. L. 1997. Granite is never isotropic: an introduction to AMS studies of granitic rocks. In Granite: From Segregation of Melt to Emplacement Fabrics (eds Bouchez, J. L., Hutton, D. H. W. & Stephens, W. E.), pp. 96–112. Dordrecht: Kluwer.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
Corry, C. E. 1988. Laccoliths–mechanics of emplacement and growth. Geological Society of America, Special Paper no. 220, 120 pp.CrossRefGoogle Scholar
Dagley, P. & Mussett, A. E. 1981. Palaeomagnetism of the British Tertiary igneous province: Rhum and Canna. Geophysical Journal of the Royal Astronomical Society 65, 475–91.CrossRefGoogle Scholar
Dagley, P., Mussett, A. E. & Skelhorn, R. R. 1984. The palaeomagnetism of the Tertiary igneous complex of Ardnamurchan. Geophysical Journal of the Royal Astronomical Society 79, 911–22.CrossRefGoogle Scholar
Dekkers, M. J. 1990. Magnetic properties of natural goethite-III Magnetic behaviour and properties of minerals origionating from goethite dehydration during thermal demagnetization. Geophysical Journal International 103, 233–50.CrossRefGoogle Scholar
Demarest, H. H. 1983. Error analysis for the determination of tectonic rotations from palaeomagnetic data. Journal of Geophysical Research 88, 4321–8.CrossRefGoogle Scholar
Donaldson, C. H., Troll, V. R. & Emeleus, C. H. 2001. Felsites and breccias in the Northern Marginal Zone of the Rum Igneous Complex: changing views ca. 1900–2000. Proceedings of the Yorkshire Geological Society 53, 167–75.CrossRefGoogle 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.CrossRefGoogle Scholar
Emeleus, C. H. 1994. 1:20 000 solid geology map of Rum, 2nd edition. Edinburgh: Scottish Natural Heritage.Google Scholar
Emeleus, C. H. 1997. Geology of Rum and the adjacent islands. Memoir of the British Geological Survey, Sheet 60 (Scotland), 170 pp.Google Scholar
Emeleus, C. H., Cheadle, M. J., Hunter, R. H., Upton, B. G. J. & Wadsworth, W. J. 1996. The Rum Layered Suite. In Layered igneous rocks (ed. Cawthorn, R. G.), pp. 403–40. Amsterdam: Elsevier.Google Scholar
Emeleus, C. H., Dunham, A. C. & Thompson, R. N. 1971. Iron-rich pigeonites from acid rocks in the Tertiary Igneous Province of Scotland. American Mineralogist 56, 940–51.Google Scholar
Emeleus, C. H. & Troll, V. In press. Excursion Guide to the Paleocene Igneous Rocks of the Isle of Rum, Inner Hebrides. Edinburgh: Edinburgh Geological Society.Google Scholar
England, R. W. 1992. The genesis, ascent, and emplacement of the Northern Arran Granite, Scotland: Implications for granitic diapirism. Geological Society of America Bulletin 104, 606–14.2.3.CO;2>CrossRefGoogle Scholar
Gamble, J. A. 1979. Some relationships between coexisting granitic and basaltic magmas and the genesis of hybrid rocks in the Tertiary central complex of Slieve Gullion, northeast Ireland. Journal of Volcanology and Geothermal Research 5, 297–316.CrossRefGoogle Scholar
Gamble, J. A., Meighan, I. G. & McCormick, A. G. 1992. The petrogenesis of tertiary microgranites and granophyres from Slieve Gullion Central Complex, NE Ireland. Journal of the Geological Society, London 149, 93–106.CrossRefGoogle Scholar
Geikie, A. 1897. The ancient volcanoes of Great Britain. London: Macmillan, 2 vols, xxiv + 477 pp., viii + 492 pp.CrossRefGoogle Scholar
Geoffrey, L., Olivier, P. & Rochette, P. 1997. Structure of a hypovolcanic acid complex inferred from magnetic susceptibility anisotropy measurements: the Western Red Hills granites Skye, Scotland, Thulean Igneous Province. Bulletin of Volcanology 59, 147–59.CrossRefGoogle Scholar
Giddings, J. W., Tarling, D. H. & Thomas, D. H. 1974. The palaeomagnetism of the Cleveland-Armathwaite Dyke, northern England. Transactions of the Nature Society, Northumberland 4, 220–6.Google Scholar
Greenwood, R. C., Donaldson, C. H. & Emeleus, C. H. 1990. The contact zone of the Rum ultrabasic intrusion: evidence of peridotite formation from magnesian magmas. Journal of the Geological Society, London 147, 209–12.CrossRefGoogle Scholar
Hall, J. M., Wilson, R. L. & Dagley, P. 1977. A palaeomagnetic study of the Mull Lava succession. Geophysical Journal of the Royal Astronomical Society 49, 499–514.CrossRefGoogle Scholar
Harker, A. 1904. The Tertiary igneous rocks of Skye. Memoir of the Geological Survey of Great Britain. Sheets 70 and 71 (Scotland), 471 pp.CrossRefGoogle Scholar
Harker, A. 1908. The geology of the Small Isles of Inverness shire. Memoirs of the Geological Survey: Scotland. Sheet 60 (Scotland), 210 pp.Google Scholar
Heider, F., Zitzelberger, A. & Fabian, K. 1996. Magnetic susceptibility and remanent coercive force in grown magnetite crystals from 0.1 μm to 6 mm. Physics of the Earth and Planetary Interiors 93, 239–56.CrossRefGoogle Scholar
Hrouda, F. 1982. Magnetic anisotropy of rocks and its applications in geology and geophysics. Geophysical Survey 5, 38–82.CrossRefGoogle Scholar
Hughes, C. J., Wadsworth, W. J. & Emeleus, C. H. 1957. The contact between Tertiary granophyre and Torridonian arkose on Minishal, Isle of Rhum. Geological Magazine 94, 337–9.CrossRefGoogle Scholar
Hughes, C. J. 1960. The Southern Mountains igneous complex, Isle of Rhum. Journal of the Geological Society, London 116, 111–38.CrossRefGoogle Scholar
Jelinek, V. 1981. Characterization of the magnetic fabric of rocks. Tectonophysics 79, T63–7.CrossRefGoogle Scholar
Judd, J. W. 1889. The Tertiary volcanoes of the Western Isles of Scotland. Quarterly Journal of the Geological Society of London 45, 187–219.CrossRefGoogle Scholar
Kirshvinck, J. L. 1980. The least-squares line and plane and the analysis of palaeomagnetic data. Geophysics Journal International 62, 699–718.CrossRefGoogle Scholar
McCormick, A. G., Fallick, A. E., Harmon, R. S., Meighan, I. G. & Gibson, D. 1993. Oxygen and hydrogen isotope geochemistry of the Mourne Mountains Tertiary Granites, Northern Ireland. Journal of Petrology 34, 1177–1202.CrossRefGoogle Scholar
Meighan, I. G. 1979. The acid igneous rocks of the British Tertiary Province. Bulletin of the Geological Survey of Great Britain 70, 10–22.Google Scholar
Meighan, I. G., Fallick, A. E. & McCormick, A. G. 1992. Anorogenic granite magma genesis: new isotope data for the southern sector of the British Tertiary Igneous Province. Transactions of the Royal Society of Edinburgh 83, 227–33.CrossRefGoogle Scholar
Merrill, R. T. & McElhinny, M. W. 1983. The Earth's Magnetic Field: Its History, Origin, and Planetary Perspective. International Geophysical Series, vol. 32. Academic Press, 401 pp.Google Scholar
O'Driscoll, B., Troll, V. R., Reavy, R. J. & Turner, P. 2006. The Great Eucrite intrusion of Ardnamurchan, Scotland: re-evaluating the ring-dyke concept. Geology 34, 189–92.CrossRefGoogle Scholar
O'Driscoll, B., Hargraves, R. B., Emeleus, C. H., Troll, V. R., Donaldson, C. H. & Reavy, R. J. 2007. Magmatic lineations inferred from anisotropy of magnetic susceptibility fabrics in Units 8, 9 and 10 of the Rum Eastern Layered Series, Scotland. Lithos 98, 27–44.CrossRefGoogle Scholar
Peacock, G. W., Petronis, M. S. & Geissman, J. W. 2006. Anisotropy of Magnetic Susceptibility and Paleomagnetism of the mid-Tertiary Three Peaks Laccolith, Iron Axis Province, Southwest Utah. Eos, Transactions of the American Geophysical Union 87 (52).Google Scholar
Richey, J. E. 1932. Tertiary ring structures in Britain. Transactions of the Geological Society of Glasgow 19, 42–140.CrossRefGoogle Scholar
Richey, J. E. & Thomas, H. H. 1930.The geology of Ardnamurchan, North West Mull and Coll. Memoirs of the Geological Survey. Scotland, Sheets 51 and 52. Edinburgh: HMSO.Google Scholar
Richter, C. & van der Pluijm, B. A. 1994. Separation of paramagnetic and ferromagnetic susceptibilities using low temperature magnetic susceptibilities and comparison with high field methods. Physics of the Earth and Planetary Interiors 82, 113–23.CrossRefGoogle Scholar
Rochette, P. 1987. Magnetic susceptibility of the rock matrix related to magnetic fabric studies. Journal of Structural Geology 9, 1015–20.CrossRefGoogle Scholar
Rochette, P., Jackson, M. & Aubourg, C. 1992. Rock magnetism and the interpretation of anisotropy of magnetic susceptibility. Reviews of Geophysics 30 (3), 209–26.CrossRefGoogle Scholar
Roy, J. L. & Park, J. K. 1974. The magnetization process of certain red beds: Vector analysis of chemical and thermal results, Canadian Journal of Earth Sciences 2, 437–71.CrossRefGoogle Scholar
Sparks, R. S. J. 1988. Petrology and geochemistry of the Loch Ba ring-dyke, Mull N. W. Scotland; an example of the extreme differentiation of tholeiitic magmas. Contributions to Mineralogy and Petrology 100, 446–61.CrossRefGoogle Scholar
Stevenson, C. T. E., Owens, W. H. & Hutton, D. W. H. 2007. Flow lobes in granite: the determination of magma flow direction in the Trawenagh Bay Granite, N. W. Ireland, using anisotropy of magnetic susceptibility. Geological Society of America Bulletin 119, 1368–86.CrossRefGoogle Scholar
Stevenson, C. T. E., Owens, W. H., Hutton, D. H., Hood, D. N. & Meighan, I. G. 2007. Laccolithic, as opposed to cauldron subsidence, emplacement of the Eastern Mourne pluton, N. Ireland: evidence from anisotropy of magnetic susceptibility. Journal of the Geological Society, London 164, 99–110.CrossRefGoogle Scholar
Tarling, D. H. & Hrouda, F. 1993. The magnetic anisotropy of rocks. London: Chapman & Hall, 217 pp.Google Scholar
Thompson, R. N. 1982. Magmatism of the British Tertiary Volcanic Province. Scottish Journal of Geology 18, 49–107.CrossRefGoogle Scholar
Troll, V. R., Emeleus, C. H. & Donaldson, C. H. 2000. Caldera formation in the Rum Igneous Complex, Scotland. Bulletin of Volcanology 62, 301–17.CrossRefGoogle Scholar
Troll, V. R., Donaldson, C. H. & Emeleus, C. H. 2004. Pre-eruptive magma mixing in intra-caldera ash-flow deposits of the Rum Igneous Centre, Scotland. Contributions to Mineralogy and Petrology 147, 722–39.CrossRefGoogle Scholar
Uyeda, S., Fuller, M. D., Belshe, J. C. & Girdler, R. W. 1963. Anisotropy of magnetic susceptibility of rocks and minerals. Journal of Geophysical Research 68, 279–91.CrossRefGoogle Scholar
Walker, G. P. L. 1975. A new concept of the evolution of the British Tertiary intrusive centres. Journal of the Geological Society, London 131, 121–41.CrossRefGoogle Scholar
Willson, R. L., Hall, J. M. & Dagley, P. 1972. The British Tertiary igneous province: palaeomagnetism of the dyke swarm along the Sleat coast of Skye. Geophysical Journal International 68, 317–23.CrossRefGoogle Scholar
Zijderveld, J. D. A. 1967. A. C. Demagnetization of rocks: Analysis of results. In Methods in Paleomagnetism (eds Collinson, D. W., Creer, K. M. & Runcorn, S. K.), pp. 254, 286. Amsterdam: Elsevier.Google Scholar