Hostname: page-component-586b7cd67f-t7czq Total loading time: 0 Render date: 2024-12-01T03:06:06.177Z Has data issue: false hasContentIssue false
  • English
  • Français

The Trawenagh Bay Granite and a new model for the emplacement of the Donegal Batholith

Published online by Cambridge University Press:  11 January 2017

Carl T. E. Stevenson ,
Donald H. W. Hutton  and
Alun R. Price
Carl T. E. Stevenson
Affiliation:
School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK, e-mail: [email protected]
Donald H. W. Hutton
Affiliation:
School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK, e-mail: [email protected]
Alun R. Price
Affiliation:
Brynanwen, Turnstone, Vowchurch, Herefordshire HR2 ORE, UK, e-mail: [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

The Trawenagh Bay Granite (TBG) is shown to be a tabular pluton with gently inclined contacts that, from anisotropy of magnetic susceptibility (AMS) studies, was emplaced as a series of flow lobes whose geometries indicate that it flowed horizontally towards the W out of late stage adjacent steeply inclined monzogranite sheets of the Main Donegal Granite (MDG). We thus confirm in detail the central broad idea of the Pitcher & Read (1959) model that the Main Donegal Granite fed the Trawenagh Bay Granite. Early TBG flow lobes cut and are cut by deformation associated with the sinistral shear zone in which the MDG lies, thus demonstrating synchronicity of shearing and magmatism. The TBG magma leaked out of the shear zone and emplaced into undeformed country rocks and was probably guided by shear zone splays that die out along its northern and southern margins. At a late stage in the development of MDG, the splays developed from the NNE-trending SW boundary of the shear zone and caused a gap in this structure through which TBG magma was channelled out of the MDG. A review is presented of the last twenty-five years of published and unpublished work on the batholith, showing that the MDG shear zone was a long-lived structure almost certainly in existence before the emplacement of that body, and that four of the contiguous granitiods (Thorr, Ardara, and Rosses, as well as Trawenagh Bay) were all sourced within the shear zone. A new model is presented for the development of the batholith. The pre-existing crustal structure was a deep-seated N12°E fault in the basement to the Dalradian wall rocks of the granites, that was coupled to up to six other more minor WNW-ESE basement faults in the W. A NE-SW-trending sinistral shear zone was initiated at the end of the Caledonian orogeny, as calc-alkaline and deep-seated appinites were generated in the area. This shearing activated the pre-existing structures at the current crustal level, and the N12°E structure acted as a continental transform fault which allowed the dilation needed to facilitate the wedging space requirements of the MDG and the other units in the shear zone, as well as transferring regional sinistral shear through the system. The Thorr and Ardara plutons were emplaced first into the shear zone and then those magmas leaked out into the adjacent wall rocks: one to form a large laccolith, the other to form a balloon. Steep early MDG complex sheets (granodiorites and tonalities) were emplaced in the shear zone between the Thorr and Ardara emplacement sites. Dilation continued until late stage extensive monzogranite sheets were intruded in the NW and SE of the pluton. One of these probably leaked material westward to form the Rosses laccolith and southwestwards to form the TBG in the final stages of shear zone movement.

Keywords

ascent and emplacementgranite emplacementlaccolithMain Donegal Granitepluton definitionshear zone
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 97 , Issue 4 , 2008 , pp. 455 - 477
Copyright
Copyright © The Royal Society of Edinburgh 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

Akaad, M.K. 1954. The Ardara granitic diapir of County Donegal. Ireland. Journal of the Geological Society, London 112, 263-88.CrossRefGoogle Scholar
Cole, G. 1902. On the composite gneisses in Boylagh, west Donegal. Proceedings of the Royal Irish Academy 24B, 203-30.Google Scholar
Condon, D.J., Bowring, S.A., Pitcher, W.S. & Hutton, D.H.W. 2004. Rates and tempo of granitic magmatism: a U-Pb geo-chronological investigation of the Donegal Batholith (Ireland). Geological Society of America, Abstracts with Programs 36, 406.Google Scholar
Gapais, D. 1989. Shear structures within deformed granites: Mechanical and thermal indicators. Geology 17, 1144-7.2.3.CO;2>CrossRefGoogle Scholar
Gindy, A. R. 1953. The plutonie history of the district around Trawenagh Bay, County Donegal. Journal of the Geological Society, London 108, 377-111.CrossRefGoogle Scholar
Halliday, A.N., Aftalion, M. & Leake, B.E. 1980. A revised age for the Donegal Granites. Nature 284, 542-3.CrossRefGoogle Scholar
Holder, M. 1979. An emplacement mechanism for post tectonic granites and its implications for their geochemical features. In Atherton, M. & Tarney, J. (eds) Origins of Granite Batholiths: Geochemical Evidence, 116-28. Nantwich: Shiva Publishing Ltd. CrossRefGoogle Scholar
Hutton, D. 1981. The Main Donegal Granite - Lateral Wedging in a Syn-Magmatic Shear Zone. Journal of Structural Geology 3 (1), 93.Google Scholar
Hutton, D.H.W. 1982. A tectonic model for the emplacement of the Main Donegal Granite, NW Ireland. Journal of the Geological Society, London 139, 615-31.CrossRefGoogle Scholar
Hutton, D.H.W. 1992. Granite Sheeted Complexes - Evidence for the Dyking Ascent Mechanism. Transactions of the Royal Society of Edinburgh: Earth Sciences 83, 377-82.CrossRefGoogle Scholar
Hutton, D.H.W. & Alsop, G.I. 1996. The Caledonian strike-swing and associated lineaments in NW Ireland and adjacent areas: Sedimentation, deformation and igneous intrusion patterns. Journal of the Geological Society, London 153, 345-60.CrossRefGoogle Scholar
Hutton, D.H.W. & Siegesmund, S. 2001. The Ardara Granite: Reinflating the Balloon hypothesis. Zeitschrift der Deuchen Geologischen Gesellschaft 152, 309-23.CrossRefGoogle Scholar
Jacques, J.M. & Reavy, R. J. 1996. Caledonian Plutonism and Major Lineaments in the Sw Scottish Highlands. Journal of the Geological Society, London 151, 955-69.CrossRefGoogle Scholar
McErlean, M.A. 1992. A new shear criterion for rocks deformed in the magmatic state: examples from the Thorr Granite, Co. Donegal. Transactions of the Royal Society of Edinburgh: Earth Sciences 83, 494.Google Scholar
McErlean, M.A. 1993. Granitoid emplacement and deformation: a case study of the Thorr pluton, Ireland, with contrasting examples from Scotland. Unpublished PhD Thesis, University of Durham, UK.Google Scholar
Meneilly, A.W. 1982. Regional structure and syntectonic intrusion in the Gweebarra Bay area, County Donegal, Ireland. Journal of the Geological Society, London 139, 633-46.CrossRefGoogle Scholar
Molyneux, S.J. 1997. Processes of granite emplacement: N W Ireland and Brazil. Unpublished PhD Thesis, University of Durham, UK.Google Scholar
Molyneux, S.J. & Hutton, D.H.W. 2000. Evidence for significant granite space creation by the ballooning mechanism: The example of the Ardara pluton, Ireland. Geological Society of America Bulletin 112 (10), 1543-58.2.0.CO;2>CrossRefGoogle Scholar
O’Connor, P.J., Long, C. B., Keenan, P.S., Halliday, A.N., Max, M. D. & Roddick, J.C. 1982. Rb-Sr isochron study of the Thorr and Main Donegal Granites, Ireland. Geological Journal 17, 279-95.CrossRefGoogle Scholar
Paterson, S.R., Vernon, R.H. & Tobisch, O.T. 1989. A review of criteria for the identification of magmatic and tectonic foliations in granitoids. Journal of Structural Geology 11 (3), 349-63.CrossRefGoogle Scholar
Paterson, S.R. & Vernon, R.H. 1995. Bursting the Bubble of Ballooning Plutons - a Return to Nested Diapirs Emplaced by Multiple Processes. Geological Society of America Bulletin 107 (11), 1356-80.2.3.CO;2>CrossRefGoogle Scholar
Pitcher, W.S. 1953a. The Rosses granitic ring complex, County Donegal. Proceedings of the Geologists’ Association 64, 153-82.CrossRefGoogle Scholar
Pitcher, W.S. 1953b. The migmatitic Older Granodiorite of the Thorr district, Co. Donegal. Quarterly Journal of the Geological Society of London 108(for 1952), 413-60.CrossRefGoogle Scholar
Pitcher, W.S. 1970. Ghost stratigraphy in intrusive granites: a review. In Newall, G. & Rast, N. (eds) Mechanisms of Igneous Intrusion. Geological Journal Special Issue 2, 141-56. Liverpool: Seel House Press.Google Scholar
Pitcher, W.S. 1997. The nature and origin of granite, 2nd edition. London: Chapman and Hall.Google Scholar
Pitcher, W.S. & Berger, A.R. 1972. The Geology of Donegal, a study of granite emplacement and unroofing. London: Wiley Interscience.Google Scholar
Pitcher, W.S. & Hutton, D.H.W. 2004. A Master Class Guide to the Granites of Donegal. The Dublin: Geological Survey of Ireland.Google Scholar
Pitcher, W.S. & Read, H.H. 1959. The Main Donegal Granite. Quarterly Journal of the Geological Society of London 64, 259-305.Google Scholar
Pitcher, W.S. & Read, H.H. 1960. The aureole of the Main Donegal Granite. Quarterly Journal of the Geological Society of London 66, 1-36.CrossRefGoogle Scholar
Price, A.R. 1997. Multiple sheeting as a mechanism of pluton construction: The Main Donegal Granite, NW. Ireland. Unpublished PhD Thesis, University of Durham, UK.Google Scholar
Price, A.R. & Pitcher, W.S. 1999. The Trawenagh Bay granite: a multipulse, inclined sheet in the flank of a synplutonic shear zone. Irish Journal of Earth Science 17, 51-60.Google Scholar
Read, H.H. 1958. Donegal granite. Science in Progress 182, 225-10.Google Scholar
Siegesmund, S. & Becker, J.K. 2000. Emplacement of the Ardara pluton (Ireland): new constraints from magnetic fabrics, rock fabrics and age dating. International Journal of Earth Sciences 89, 307-27.CrossRefGoogle Scholar
Stevenson, C.T.E. 2004. Magma Flow and Granite emplacement in Contrasting Tectonic Environments using Anisotropy of Magnetic Susceptibility. Unpublished PhD Thesis, University of Birmingham, UK.Google Scholar
Stevenson, C.T.E., Owens, W.H. & Hutton, D.H.W. 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 (11-12), 1368-86.CrossRefGoogle Scholar
Vernon, R.H. & Paterson, S.R. 1993. The Ardara pluton, Ireland: deflating an expanded intrusion. Lithos 31, 17-32.CrossRefGoogle Scholar
Vigneresse, J.L. 1995. Control of Granite Emplacement by Regional Deformation. Tectonophysics 249, 173-86.CrossRefGoogle Scholar
Vigneresse, J.L., Barbey, P. & Cuney, M. 1996. Rheological transitions during partial melting and crystallization with application to felsic magma segregation and transfer. Journal of Petrology 37, 1579-600.CrossRefGoogle Scholar
Watson, J. 1982. The ending of the Caledonian orogeny in Scotland. Journal of the Geological Society, London 141, 193-214.CrossRefGoogle Scholar
Whitten, E.H.T. 1957. The Gola granite (County Donegal) and its regional setting. Proceedings of the Royal Irish Academy 58B, 245-92.Google Scholar