Hostname: page-component-7c8c6479df-7qhmt Total loading time: 0 Render date: 2024-03-29T11:43:41.327Z Has data issue: false hasContentIssue false

Structural and stratigraphic relationships across the continuation of the Highland Boundary Fault in western Ireland

Published online by Cambridge University Press:  17 March 2003

D. M. CHEW
Affiliation:
Department of Geology, University College Dublin, Belfield, Dublin 4, Ireland Present address: Department of Geology, Trinity College Dublin, Dublin 2, Ireland; email: chewd@tcd.ie

Abstract

The relationship between the Dalradian Supergroup and the Highland Border Complex in Scotland has remained contentious for over a century. In western Ireland, the contact between the Dalradian Supergroup and the Clew Bay Complex (a correlative of the Highland Border Complex) is superbly exposed on the island of Achill Beg on the North Mayo coast. The unfossiliferous South Achill Beg succession has been traditionally assigned to the Clew Bay Complex, and this interpretation is supported by a combination of Sm–Nd model age data, heavy mineral analysis and lithostratigraphic correlation. TDM ages range from 1.99–2.66 Ga (mean=2.28 Ga, n=6). Detailed structural mapping shows that both the Dalradian and the Clew Bay Complex share the same structural history. A D1 high strain event is common to both units, and is associated with the development of tectonic slides. The D2 event is responsible for the formation of crustal-scale nappes. In both units, beds are consistently downward facing on the S2 foliation. Later dextral shearing (D3) resulted in the tilting of the originally recumbent, S-facing D2 nappes into this downward-facing orientation. Rb–Sr and 40Ar–39Ar radiometric dating of muscovite confirms that both units were deformed contemporaneously as the S2 nappe fabric in each is dated at c. 460 Ma. This Middle Ordovician age for deformation of the Clew Bay Complex is highly significant, not least because published microfossil data suggest a Silurian age.

Type
Research Article
Copyright
© 2003 Cambridge University Press

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.)