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 Figures Only Full Text Full Text (PDF) 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 Web of Science (7) Citing Articles via Google Scholar Google Scholar Articles by Hutton, D.H.W. Articles by Alsop, G.I. Search for Related Content GeoRef GeoRef Citation

Evidence for a major Neoproterozoic orogenic unconformity within the Dalradian Supergroup of NW Ireland

^{1 1}School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
^{2 2}Crustal Geodynamics Group, School of Geography & Geosciences, University of St. Andrews, St Andrews KY16 9AL, UK (e-mail: gia@st-andrews.ac.uk)

An intriguing and contradictory scenario has recently developed in the Caledonides of the British Isles concerning the ages of deposition and deformation of the Neoproterozoic Dalradian Supergroup. Isotopic evidence, although limited, suggests that the lower parts of the sequence may have been deposited and undergone Precambrian deformation (i.e. pre-600 Ma) prior to deposition of the upper parts of the sequence (i.e. post-600 Ma). Given these existing constraints, it is clear that a major break (or breaks) would be required in the intervening sequence to maintain a coherent tectonostratigraphy. We present evidence for such an unconformity preserved at the base of the Easdale Subgroup in NW Ireland. Reworked clasts that contain a pre-existing tectonometamophic history are identified within a conglomerate that lies along this regionally recognized boundary. The underlying sequence also exhibits pre-existing deformational fabrics that display erosional truncation at the base of the conglomerates. These relationships, together with significant erosion and excision of the footwall sequence, and extensive thickness and facies variations in the hanging-wall units, imply that a major tectonic unconformity exists within this succession. As the conglomerate lies stratigraphically below Precambrian (c. 600 Ma) lavas, the structural fabrics contained within the clasts and the underlying sequence must also be of Precambrian age and totally unrelated to the well-established Early Palaeozoic (Caledonian) orogenic deformation observed in the younger parts of the sequence. The Dalradian Supergroup, as defined, may actually comprise (at least) two distinct tectonostratigraphic sequences.

KEYWORDS: Caledonides, Dalradian, Ireland, orogeny, unconformity

This article has been cited by other articles:

				A. G. Leslie, M. Smith, and N.J. Soper Laurentian margin evolution and the Caledonian orogeny--A template for Scotland and East Greenland Geological Society of America Memoirs, January 1, 2008; 202(0): 307 - 343. [Abstract] [Full Text] [PDF]

				P. W. G. Tanner, P. W. G. Tanner, A. G. Leslie, and M. R. Gillespie Structural setting and petrogenesis of the Ben Vuirich Granite Pluton of the Grampian Highlands: a pre-orogenic, rift-related intrusion Scottish Journal of Geology, November 1, 2006; 42(2): 113 - 136. [Abstract] [PDF]

				A. G. Leslie, A. G. Leslie, M. Krabbendam, and R. A. Smith The Gaick Fold Complex: large-scale recumbent folds and their implications for Caledoniari structural architecture in the Central Grampian Highlands Scottish Journal of Geology, November 1, 2006; 42(2): 149 - 159. [Abstract] [PDF]

				G.A. McCay, A.R. Prave, G.I. Alsop, and A.E. Fallick Glacial trinity: Neoproterozoic Earth history within the British-Irish Caledonides Geology, November 1, 2006; 34(11): 909 - 912. [Abstract] [Full Text] [PDF]

				MichaelJ. Flowerdew, J.S. Daly, and MartinJ. Whitehouse 470 Ma granitoid magmatism associated with the Grampian Orogeny in the Slishwood Division, NW Ireland Journal of the Geological Society, May 1, 2005; 162(3): 563 - 575. [Abstract] [Full Text] [PDF]

				P.W.G. Tanner, G.I. Alsop, and D.H.W. Hutton Discussion on evidence for a major Neoproterozoic orogenic unconformity within the Dalradian Supergroup of NW Ireland Journal of the Geological Society, January 1, 2005; 162(1): 221 - 224. [Full Text] [PDF]