Further evidence for Devono-Carboniferous rifting in Central Ireland

Abstract

Based on the body of available data it is argued that the Irish midland Devono-Carboniferous developed as a graben structure of the type currently exhibited at the Red Sea/African and Rhine upwarp systems. Evidence, both data-based and inferential, is drawn from studies of basement framework, regional Devono-Carboniferous stratigraphy and inferred palaeogeography, igneous geology, geophysical (gravity) patterns and known Irish Devono-Carboniferous fault systems. Examples of two of the latter are presented. This Irish central graben is argued to have developed in Late Devonian times along the axìs of a crustal upwarp inferred to have resulted from plate collision during Late Ordivician to Early Devonian times. It is hypothesized that rifting may have been preceeded by possible deepseated carbonatite intrusion along the upwarp axis, possibly coeval with and/or following intrusion of the Late Caledonian Irish granites. Carbonatite evidence may have been subsequently destroyed by intrusion of 'embryonic spreading centre' magmas, so providing a possible explanation for present day regional Irish gravity values. For reasons presently unknown this 'foetal' spreading centre failed, the rift tilled and subsequent (Hercynian) overthrusting and crustal shortening has resulted in Irish regional geology as it is today.