The crustal structure and regional development of the Irish Atlantic margin region

Abstract

Duringthe past decade, asuiteofwide-angleseismic reflection/refraction profileshasbeens hot in the Porcupine, Rockall andH atton basins,a sw ell asacross the Hatton continentalm argin. Integration ofthe wide-angleseismic datawithnormal-incidence reflection profilesandwithgravity andmagnetic datareveals a clearpictureofthe regionalcrustalanduppermantlestructure, andofthe large-scalesedimentary geometry ofthe LatePalaeozoic-Cenozoic basins inthe area.The region contains asetoflarge sedimentary basins restingupon variably thinned continentalcrust. The crust beneaththe basin-boundingstructuralhighsist ypically around 25kmthick, withthe crust beneaththe basins beingasthinas6km. The PorcupineBasincontains up to 10 kmof sediments. Upt o7kmo fsedimentary strataa rei ndicated int he Rockall Basin,with4kmo fsediment int he Hatton Basin. Severalseismicallydistinctlayers,withP-wavevelocitiesof1.8-5.3 kms 2 1 ,wereidentified above the basement inthe sedimentary basins. Asignificant variability inthickness ofthe sedimentary layers isseenon the wide-angledata.Thesereflectthe presence ofanumberofolderMesozoic riftsedimentary basins. The wideangledatarevealmarked topographicirregularity atthe baseofthe sedimentary succession inthe Rockall Basin, interpreted asthe result ofextensivemulti-phaseMesozoic rifting.The Mohobeneaththe Rockall Basinshows a clearasymmetry,withasteepergradient alongthe eastern marginofthe basin. The continent-oceanboundary west ofthe Hatton High hasasignificant underplated andvolcanic component,whilethatatthe southern margin ofthe Rockall Basinshows evidence ofagreatertranspressivecomponent. The natureofthe lowercrust appears to exert acontrollinginfluence on the location ofcrustalseparation. Inareaswherethinningisaccommodated by upperandmiddlecrustalattenuation,the strengthofthe uppercrust (andunderlyingbrittlemantle)hasserved to preservethe integrity ofthe continentalcrust andinhibitseafloor spreading.However,wherethe lowercrust is thinned significantly,asbeneaththe Hatton continentalmargin,crustalseparation hastakenplace eventhough the upperandmiddlecrust remains relatively thick.

Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

“…In general, seismic studies have identified two crustal layers with low seismic velocity values representative of their continental affinity. However, the rifting processes that led to the formation of continental fragments and microcontinents most likely affect their layers and entire thicknesses (Morewood et al, 2005), as well as adding mafic intrusions to the crust. From 36 geophysical studies of continental fragments we determine an average crustal thickness of ∼ 24.8 ± 5.7 km (Table 5).…”

“…In this region, continental fragments are accreting and colliding with arcs and (2003), (6) Klingelhoefer et al (2007), (7) Funck (2003), (8) Gerlings et al (2011), (9) Fowler et al (1989), (10) Breivik et al (2012), (11) Lebedeva-Ivanova et al (2006), (12) Morewood et al (2005), (13) Vogt et al (1998), and (14) Collier et al (2009). other continental fragments. The North Palawan block is the best example of a passive margin fragment currently impinging on an island arc (the Philippine Mobile Belt).…”

“…Bulk densities are also reported from studies where the authors combined gravity and seismic data to determine crustal density. References are (1) Funck et al (2008), (2) Grobys et al (2007), (3) Cooper et al (1981), (4) Grobys et al (2009), (5) Borissova et al (2003), (6) Klingelhoefer et al (2007), (7) Funck (2003), (8) Gerlings et al (2011), (9) Fowler et al (1989), (10) Breivik et al (2012), (11) Lebedeva-Ivanova et al (2006), (12) Morewood et al (2005), (13) Vogt et al (1998), and (14) Collier et al (2009 In the geological record, large volumes of crustal accretion are carried out by the collision of composite terranes or continental fragments onto continents (Vink et al, 1984). In North America, the amalgamation of the Wrangellia and Stikinia terranes resulted in a ribbon continent (SABIYA) that was ∼ 8000 km long and ∼ 500 km wide (Johnston, 2001).…”

Comparison of lithosphere structure across the Orphan Basin–Flemish Cap and Irish Atlantic conjugate continental margins from constrained 3D gravity inversions

“…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.…”

Controls on the location of compressional deformation on the NW European margin

“…Seismic refraction data indicate that the crystalline crust beneath the southern part of the Rockall Basin is typically 5-7 km thick Morewood et al 2005). This is underlain by a 3-10 km-thick zone with P-wave velocities of 7.5-7.8 km s 21 , which was interpreted as a partially serpentinized upper mantle by O'Reilly et al (1996).…”