Abstract:Summary
VARNET, an international multidisciplinary project, was designed to examine the ‘Variscan Front’ in the southwest of Ireland. As part of the seismic experiment a 200 km long wide‐angle seismic profile (Line A) was recorded from the Old Head of Kinsale in the south of Ireland to Galway Bay on the west coast. Along Line A, 170 seismic stations were deployed at approximately 1 km intervals.
Results from ray trace modelling indicate a multilayered crust. The upper crust, extending to a depth of about 14 km… Show more
“…The Irish continental shelf and many of the basins therein have been the focus of seismic reflection, seismic refraction and potential field investigations for several decades (Holder & Bott 1971;Whitmarsh et al 1974;Bunch 1979;Jacob et al 1985;Makris et al 1988;Roberts et al 1988;Lowe & Jacob 1989;O'Reilly et al 1991O'Reilly et al , 1995O'Reilly et al , 2010Vogt et al 1998;Landes et al 2000Landes et al , 2003Morewood et al 2005;Hauser et al 2008). Coupled with sparse well control, the resulting studies have allowed for the piecing together of the detailed tectonostratigraphic basin evolution of the margin (Shannon 1991;Naylor & Shannon 2009.…”
Regionally constrained 3D gravity inversion results on the Orphan Basin-Flemish Cap and the Irish Atlantic conjugate continental margins are compared to investigate crustal structure, early rifting history and geological evolution of this part of the North Atlantic. The full-crustal density anomaly distributions provide some of the first depth images of how rifted structures compare along and across these conjugate margins. Broad similarities in crustal structure are identified with some noticeable differences, linked to rifting and crustal stretching processes. Extreme crustal thinning (stretching factors >3.5) is indicated beneath much of the southern Porcupine Basin, the western half of West Orphan Basin, the eastern half of Jeanne d'Arc Basin, the southeastern half of East Orphan Basin and in pockets beneath Rockall Basin. This appears to have resulted in the serpentinization (and possible exhumation) of mantle lithosphere on the Irish Atlantic and Flemish Cap margins but not beneath Orphan Basin. A simple evolution model is proposed for the early stages of rifting between the margins. It is suggested that ancient orogenic sutures played an important role in controlling the northward migration of rifting and the rotation and displacement of Flemish Cap out of Orphan Basin.Supplementary material: Enlarged maps from this paper are available at www.geolsoc.org.uk/SUP18527.
“…The Irish continental shelf and many of the basins therein have been the focus of seismic reflection, seismic refraction and potential field investigations for several decades (Holder & Bott 1971;Whitmarsh et al 1974;Bunch 1979;Jacob et al 1985;Makris et al 1988;Roberts et al 1988;Lowe & Jacob 1989;O'Reilly et al 1991O'Reilly et al , 1995O'Reilly et al , 2010Vogt et al 1998;Landes et al 2000Landes et al , 2003Morewood et al 2005;Hauser et al 2008). Coupled with sparse well control, the resulting studies have allowed for the piecing together of the detailed tectonostratigraphic basin evolution of the margin (Shannon 1991;Naylor & Shannon 2009.…”
Regionally constrained 3D gravity inversion results on the Orphan Basin-Flemish Cap and the Irish Atlantic conjugate continental margins are compared to investigate crustal structure, early rifting history and geological evolution of this part of the North Atlantic. The full-crustal density anomaly distributions provide some of the first depth images of how rifted structures compare along and across these conjugate margins. Broad similarities in crustal structure are identified with some noticeable differences, linked to rifting and crustal stretching processes. Extreme crustal thinning (stretching factors >3.5) is indicated beneath much of the southern Porcupine Basin, the western half of West Orphan Basin, the eastern half of Jeanne d'Arc Basin, the southeastern half of East Orphan Basin and in pockets beneath Rockall Basin. This appears to have resulted in the serpentinization (and possible exhumation) of mantle lithosphere on the Irish Atlantic and Flemish Cap margins but not beneath Orphan Basin. A simple evolution model is proposed for the early stages of rifting between the margins. It is suggested that ancient orogenic sutures played an important role in controlling the northward migration of rifting and the rotation and displacement of Flemish Cap out of Orphan Basin.Supplementary material: Enlarged maps from this paper are available at www.geolsoc.org.uk/SUP18527.
“…Also, very little is known about the deep structure of this fault zone. A northward dipping reflector on the BIRPS seismic profile due west of the Shannon Estuary has been interpreted as the structural trace of the ISZ [Klemperer, 1989], while Lowe and Jacob [1989] and Landes et al [2000] Abramovitz et al [1999] concluded that, based on seismic evidence, the ISZ formed due to anti-clockwise rotation of the Eastern Avalonian continent, and subsequent drift and subduction of Laurentia under Eastern Avalonia, with a south-dipping reflector in the upper mantle [Landes et al, 2000].…”
Section: Pages 337340-341mentioning
confidence: 99%
“…During theVARNET-96 controlled source exper iment in southern Ireland [Masson et al, 1999;Landes et al, 2000], teleseismic P-waves from distant earthquakes and nuclear test explosions were also recorded. A significant anomaly in the variation of P-wave travel time residuals of magnitude about 1.0 s co-incide with the pos tulated surface trace of the Caledonian ISZ.…”
The Irish Seismological Lithospheric Experiment (ISLE 2002) has been designed to investigate the deep lithospheric and asthenospheric structure across the late‐Caledonian Iapetus Suture Zone in southern Ireland. The project is a collaboration between the Dublin Institute for Advanced Studies (DIAS), Ireland, and the Geophysical Institute (GPI) of the University of Karlsruhe, Germany. This is the first passive teleseismic experiment conducted in Ireland, building upon a large body of earlier work on the crustal structure offshore and onshore Ireland, based on controlled source seismics and potential field studies.
“…The Munster Basin is generally considered to have evolved as an E–W‐orientated half‐graben comprised of thick Devonian sediments (Husain 1957; Todd 1989; Williams et al 1989). The presence of outcropping sediments to the south of the Killarney–Mallow Fault Zone indicates that down‐to‐the‐south displacement occurred on the fault and a southerly dip is inferred for this structure (Landes et al 2000; Vermeulen et al 2000). Variscan inversion may explain the presence of shallow upper crust in the hangingwall of the Killarney–Mallow Fault Zone.…”
Section: Geological and Tectonic Settingmentioning
confidence: 99%
“… Fence diagram of the crust and upper mantle structure of the southwest of Ireland using available onshore and offshore seismic refraction/wide‐angle reflection data recorded in the period of 1982–1996. The VARNET‐96 profiles (Masson et al 1998; Landes et al 2000), COOLE85‐P1 (Lowe & Jacob 1989) and COOLE85‐P6 (O'Reilly et al 1991) were deployed perpendicular to the E–W Variscan trend while the ICSSP82 (Jacob et al 1985), COOLE85‐P7 (along the axis of the North Celtic Sea Basin; O'Reilly et al 1991) and COOLE85‐P3a (Makris et al 1988) profiles run approximately parallel to strike of the predominant NE–SW Caledonian trend. ICSSP82 intersects both line A and COOLE85‐P1.…”
SUMMARY
During the VARNET‐96 seismic experiment three seismic refraction/wide‐angle reflection profiles were acquired in order to examine the crustal structure in the southwest of Ireland. A total of 170 seismic stations were used on 300 recording sites. The shotpoint geometry was designed to allow for inline and offline fan shot recordings on the three profiles, using a total of 34 shots. Results from 3‐D ray‐trace and inversion modelling illustrate the pervasive lateral heterogeneity of the crust south of the Shannon Estuary. About 5 km of interpreted Palaeozoic sediment at the south coast was associated with the sedimentary infill of the Munster and South Munster Basins. This sedimentary layer, which thins to approximately 2 km in the northern Munster Basin, is significantly thinner than previously estimated from geological field studies. High‐velocity zones beneath Dingle Bay and the Kenmare River region may be associated with the deep traces of the Killarney–Mallow Fault Zone and the Cork–Kenmare line. A zone of high‐velocity upper crust (6.4–6.6 km s−1) beneath the South Munster Basin is found in the area between the Kenmare–Killarney and the Leinster Granite gravity lows. The depth to the Moho varies from approximately 28–29 km at the south coast to approximately 32–33 km in the Dingle–Shannon Basin. The interpretation of the 2‐D and 3‐D velocity models suggests that Variscan deformation is confined to sedimentary and upper crustal structures in the southwest of Ireland.
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