Initiation and early development of the Dingle Basin, SW Ireland, in the context of the closure of the Iapetus Ocean

Abstract

Abstract The Dingle Basin of southwest Ireland lies within 40 km of the present-day trace of the Iapetus Suture. Its late Silurian fill (Dunquin Group and lower Dingle Group) is an important and, in many aspects, unique record of late Caledonian development in the Irish and British sector of the orogen. The upper Wenlock-upper Ludlow Dunquin Group comprises shallow-marine to non-marine siliciclastic and volcanic rocks (acid pyroclastic deposits and predominantly andesitic lavas) deposited on and around a volcanic island(s), whereas the lower, upper Ludlow-Přídolí, part of the overlying Dingle Group comprises sandstones, mudstones and minor conglomerates deposited in lacustrine, lake margin and succeeding fluvival systems. The change from marine Dunquin Group to non-marine Dingle Group (Old Red Sandstone) sedimentation is interpreted to have been tectonically driven. The succession is interpreted in terms of four phases of basin evolution: (1) a phase related to active subduction; (2) a phase related to subduction termination; (3) a post-subduction thermal subsidence phase; (4) a phase of strike-slip fault-controlled subsidence. In the broader, late-Caledonian context, the Dunquin Group volcanic rocks and associated sediments are interpreted as representing localized subduction of a final vestigial portion of Iapetus oceanic crust. The later, inferred, strike-slip influence in the basin is believed to be part of the well-documented regional strike-slip regime affecting this sector of the Caledonides.