Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

Journal of the Geological Society

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by BOTT, M. H. P. Articles by TANTRIGODA, D. A. Search for Related Content GeoRef GeoRef Citation

Interpretation of the gravity and magnetic anomalies over the Mull Tertiary intrusive complex, NW Scotland

Department of Geological Sciences, University of Durham, South Road, Durham DH1 3LE, UK

A 50 mGal local positive gravity anomaly over the Mull intrusive complex is interpreted as caused by an underlying dense body of mafic (basic and/or ultrabasic) rocks extending to a depth of between 6.5 and 13 km and occupying a volume of between 2000 and 3600 km³, depending on density contrast. The granites produce smaller superimposed negative gravity anomalies, which indicate that the granites of the late Loch Bà centre extend to a depth of about 2 km and those of the early Glen More centre occupy a significantly smaller volume. The granites occupy between 5 and 9% of the total volume, consistent with a derivative origin.

The complicated aeromagnetic anomalies have been simplified by applying the pseudogravimetric transformation. The most conspicuous positive pseudogravimetric anomaly occurs over the rocks of centres 1 and 2. This is of much smaller areal extent than the positive gravity anomaly, and it is attributed to highly magnetic rocks extending to a depth of about 2 km beneath centres 1 and 2, including cone sheets. The magnetization of the deeper parts of the complex is much weaker and has not been resolved. A partial ring of linear or arcuate negative magnetic anomalies occurs along the SE, S and W margins of the deep-seated intrusive complex and may mark an unexposed early ring dyke with strong reverse magnetization.

It is estimated that up to a quarter of the volume occupied by the intrusive complex may have been provided by various types of forceful intrusion but that most of the upper crustal space has been made available by ring subsidence and other types of stoping. This is feasible because the magma was demonstrably lower in density than the Moine and Lewisian. The mantle-derived magma probably rose through the more ductile lower crust by diapirism, thereby causing a slight thickening of the underlying crust which may provide isostatic support for the excess mass of the intrusive complex and its associated topography.

This article has been cited by other articles:

				L. Geoffroy, C. Aubourg, J.-P. Callot, and J.-A. Barrat Mechanisms of crustal growth in large igneous provinces: The north Atlantic province as a case study Geological Society of America Special Papers, January 1, 2007; 430(0): 747 - 774. [Abstract] [Full Text] [PDF]

				S. J. FOWLER, W. A. BOHRSON, and F. J. SPERA Magmatic Evolution of the Skye Igneous Centre, Western Scotland: Modelling of Assimilation, Recharge and Fractional Crystallization J. Petrology, December 1, 2004; 45(12): 2481 - 2505. [Abstract] [Full Text] [PDF]

				N. R. GOULTY, A. J. DOBSON, G. D. JONES, S. A. AL-KINDI, and J. G. HOLLAND Gravity evidence for diapiric ascent of the Northern Arran Granite Journal of the Geological Society, September 1, 2001; 158(5): 869 - 876. [Abstract] [Full Text] [PDF]

				A. C. Kerr, R. W. Kent, B. A. Thomson, J. K. Seedhouse, and C. H. Donaldson Geochemical Evolution of the Tertiary Mull Volcano, Western Scotland J. Petrology, June 1, 1999; 40(6): 873 - 908. [Abstract] [Full Text] [PDF]

				R. W. H. BUTLER and D. H. W. HUTTON Basin structure and Tertiary magmatism on Skye, NW Scotland Journal of the Geological Society, December 1, 1994; 151(6): 931 - 944. [Abstract] [PDF]

				D. A. Abraham and J. D. Ritchie The Darwin Complex, a Tertiary igneous centre in the Northern Rockall Trough Scottish Journal of Geology, December 1, 1991; 27(2): 113 - 125. [Abstract] [PDF]

				D. Evans, D. A. Abraham, and K. Hitchen The Geikie igneous centre, west of Lewis: its structure and influence on Tertiary geology Scottish Journal of Geology, March 1, 1989; 25(3): 339 - 352. [Abstract] [PDF]

				S. W. GARRETT, M. P. MASLANYJ, and D. DAMASKE Interpretation of aeromagnetic data from the Ellsworth Mountains-Thiel Mountains ridge, West Antarctica Journal of the Geological Society, December 1, 1988; 145(6): 1009 - 1017. [Abstract] [PDF]

				L. Kristjansson and J. Helgason Some properties of basalt lava sequences and volcanic centres in a plate-boundary environment Geological Society, London, Special Publications, January 1, 1988; 39(1): 147 - 155. [Abstract] [PDF]

				M. P. Tate and M. R. Dobson Syn- and post-rift igneous activity in the Porcupine Seabight Basin and adjacent continental margin W of Ireland Geological Society, London, Special Publications, January 1, 1988; 39(1): 309 - 334. [Abstract] [PDF]