Sedimentary provenance of the Upper Devonian Old Red Sandstone of southern Ireland: An integrated multi-proxy detrital geochronology study

Abstract

The Devonian Old Red Sandstone (ORS) magnafacies of southern Ireland is hosted in the Lower Devonian Dingle Basin and the Upper Devonian Munster Basin. Following the closure of the Iapetus Ocean during the Caledonian Orogeny, the Dingle Basin developed as a pull-apart structure before being deformed by Acadian tectonic activity. The Munster Basin developed as a half-graben structure in response to post-Acadian N-S extension in the region. Thus, the Irish ORS provides insights into the region's tectonic history due to its temporal and spatial proximity to the Caledonian (∼475-425 Ma), Acadian (∼400-390 Ma) and Variscan orogenic events (∼390-290 Ma). This study presents the first detrital zircon and apatite U-Pb geochronological data for the UORS in southern Ireland in addition to detrital white mica 40 Ar/ 39 Ar geochronological data to help unravel the depositional history of the Irish UORS and to assess the possible role of sedimentary recycling in Upper Devonian basin development.  Most Upper ORS (UORS) samples contain few late Neoproterozoic detrital zircon grains and are instead dominated by early Palaeozoic and ca. 1.1 Ga zircons. These populations represent recycling of northerly-derived Ordovician to Silurian strata of the Southern-Uplands-Longford-Down terrane which are of Laurentian affinity, and not recycling of Lower ORS (which contain a significant number of late Neoproterozoic detrital zircons) as previously thought. Similar detrital zircon dates have been observed in Givetian-Frasnian quartzites of the Pulo do Lobo Zone on the Iberian Peninsula, providing a possible Rheic Ocean link with the UORS.