Evidence for Cenozoic tectonic deformation in SE Ireland and near offshore

An integrated study of topography, bathymetry, high-resolution aeromagnetic data, and structural observations demonstrates significant Cenozoic fault activity in SE Ireland. Tectonically generated knickpoints and reddened fault breccias along topographic escarpments that are underlain by greywacke bedrock and trend oblique to the regional Caledonian strike provide evidence for fault displacement. Near-offshore faults with similar geometry produce present-day bathymetric scarps and localized tectonic topography in the inverted Kish Bank Basin. The integration of offshore high resolution aeromagnetic data and structural interpretation of the Kish Bank Basin provides evidence for dextral transtension on NNW trending faults and sinistral transpression on ENE trending faults bounding a lower Paleozoic to Carboniferous basement block. These faults correlate onshore with previously recognized Caledonian faults producing topographic offsets and surface uplift. To the north, offshore structures can be traced onshore and cut exposures of the Caledonian Leinster Granite. Structural analysis of these outcrops indicates post-Variscan deformation. A major fault on the NW margin of the batholith cuts a major erosion surface developed on Carboniferous carbonate rocks, and nonmarine Miocene deposits are preserved above this surface. Fault kinematics provide evidence of two paleostress systems: (1) NW-SE σ1, subvertical σ2 and NE-SW σ3 followed by (2) a clockwise swing of σ1 to NNW-SSE. Timing of deformation in both stress systems is probably post-Oligocene age. The mechanism driving this deformation is likely ridge-push. Much is already known about Cenozoic tectonics and exhumation from offshore basins. This study shows that onshore Ireland has also been affected by significant tectonic activity and exhumation during the Cenozoic

Structural, Remote Sensing and Multivariate Correlation Methods as Aids to Mineral Exploration, Central Ireland

This work discusses structural, remote sensing and multivariate correlation methods as aids to mineral exploration in West Central Ireland. The work was performed as part of the EU-funded CREST project

Evidence for post-early Eocene tectonic activity in southeastern Ireland

The role played by Cenozoic deformation in denudation and landscape development in Ireland has historically been difficult to assess because of the lack of widespread pre-glacial Cenozoic deposits onshore. Here we combine analysis of apatite fission-track data and geomorphic observations to place constraints on the timing, kinematics and magnitude of onshore deformation in southeastern Ireland. Relationships between apatite fission-track central age and elevation for samples from the Wicklow and Blackstairs Mountains and Tullow Lowland suggest that these rocks record an exhumed apatite partial annealing zone, which after cooling was dismembered by differential vertical displacements of up to several hundred metres. We use inverted models of sample thermal history to show that samples across the region experienced very similar thermal histories up to and including a cooling event in late Paleocene or early Eocene time. This effectively rules out strongly spatially heterogeneous denudation, and implies that differential rock uplift occurred in post-early Eocene time. The central age–elevation relationships define at least three spatial domains with internally consistent apatite fission-track data, separated by known faults or topographic escarpments. Geomorphic analysis of these structures shows that patterns of catchment incision and sinuosity, as well as the presence of antecedent drainage, are best explained by differential vertical displacements at or near the domain boundaries. The kinematics and magnitudes of these displacements are consistent with those implied by the apatite fission-track results, and are compatible with other examples of known Cenozoic deformation from Ireland and the adjacent continental margin

The post-Variscan thermal and denudational history of Ireland.

The thermal and denudational history of Ireland is evaluated using an extensive new apatite fission-track (AFT) dataset derived from surface samples. Modelled thermal histories are used to construct maps of denudation for a number of time slices from Triassic time to 10 Ma using a time-dependent palaeogeotherm. The maps illustrate the spatial variability of denudation and subsidence within each time slice. The patterns of denudation are complex, showing considerable variability at the length scale of 101–102 km, with especially high denudation rates found over known igneous centres such as the Mournes of County Down. Based on the onshore AFT data alone, there is no definitive signature of an Irish Sea Dome extending significantly across Ireland in Early Tertiary time. The cumulative amount of denudation during Tertiary time varies depending on the AFT annealing model used, but is generally in the region between 1 and 2 km and without clear spatial trends. High amounts of denudation have been mapped over the Tertiary intrusions in County Down, reflecting their unroofing since emplacement in Paleocene time. The cumulative denudation from Triassic time to 10 Ma shows relatively low amounts of denudation (<2 km) in the Irish Midlands and the extreme NE of the island, consistent with the observation that Mesozoic-Tertiary sediments and igneous products are preserved in the Ulster Basin. The western flank of Ireland and the region between Dublin and County Down show high cumulative amounts of denudation (<4 km), the latter being consistent with the high amounts of denudation interpreted for the Irish Sea region. This denudation pattern explains in part the outcrop of Precambrian and Lower Palaeozoic rocks in these areas. The spatial integration of the denudation over the entire landmass gives the average denudation rate and the sediment discharge from Ireland as a function of time. Average denudation rates are moderately high in Triassic time, falling to low values in Cretaceous time, and increasing substantially in Tertiary time. However, the total volumetric discharge of sediment in Tertiary time is an order of magnitude smaller than the preserved solid volume of Tertiary sediment in the basins offshore western Ireland