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Anne Chabert, DIAS/UCD (Ireland)
Celine Ravaut, DIAS (Ireland)
Brian M. O'Reilly, DIAS (Ireland)
Peter W. Readman, DIAS (Ireland)
Patrick M. Shannon, UCD (Ireland)
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The continental rifted margin in the North Atlantic, west of Ireland, contains a number of large Late Palaeozoic to Cenozoic sedimentary basins affected by several rifting episodes ultimately leading to continental break-up in Late Paleocene time. The Hatton Basin is located on the Irish volcanic continental passive margin and suffered extension, probably in the Late Jurassic followed by thermal effects during the Cenozoic. However, the Hatton Basin remains virtually unexplored and is poorly understood. The presence of Paleogene lavas and intrusive rocks acts as an acoustic layer masking the underlying geology, and severely limits the penetration of near-vertical seismic reflection energy.
To overcome the problem, in 2002 the HADES (HAtton DEep Seismic) experiment was carried out in the Hatton Region using Ocean Bottom Seismometers (OBS). The experiment was designed to yield sufficiently large source/receiver offsets to record waves travelling beneath or through the igneous layers. One hundred OBS were deployed with a spacing of about 3 km along a 350 km long profile in the basin providing an exceptionally large amount of wide-angle seismic data. A two-step tomographic approach was applied on these data. First, first-arrival traveltime inversion was used to define a background velocity model. This model was then used as an input model to define the Moho interface using a forward modelling method with pronounced PmP reflections.
Recently acquired seismic reflection data in the Hatton Basin have also been reprocessed and integrated with the results of the tomographic inversion in order to better constrain the sedimentary sequence in the basin.
The results show a 5 km thick two-layer sedimentary succession overlying an approximately 15 km thick three-layer crust. The sedimentary succession is interpreted as Jurassic to Recent syn- and post-rift sediments. The geometry and velocity structure suggests the presence of a major regional unconformity within the sedimentary succession, consistent with an episode of uplift and erosion during Early Cenozoic times when major volcanic activity during continental breakup occurred along the Hatton Continental Margin. This volcanic event had a great influence on the Hatton Basin with the presence of magmatic intrusions and several major central igneous complexes in the basin. Most of the crustal extension is interpreted to have occurred during two different time intervals, one during early Mesozoic (pre-Cretaceous) intracontinental rifting common to the rest of the Irish Margin, and the second during early Cenozoic extension connected with the continental breakup to the west along the margin before a return to deep marine condition in late Eocene time.
This project is funded by the Geological Survey of Ireland and the Irish Petroleum Infrastructure Programme.
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