Deep crustal reflectors under Reydarfjördur, eastern Iceland:crustal accretion above the Iceland mantle plume

Smallwood, John R.; White, R. S.; Staples, Robert K.

doi:10.1046/j.1365-246x.1998.00593.x

Cited by 34 publications

(15 citation statements)

References 42 publications

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“…However, synthetic seismograms indicate that the seismic response of a thin lava flow package depends on interference between reflections within multiple flow units. Packages of compositionally similar lava flows tend to be of similar thickness and these generate strong reflections similar to those from single, thick beds [ Smallwood et al , 1998]. The major velocity intervals recovered by the waveform inversion are therefore probably best interpreted as averages for the compositionally similar packages of lava flows concerned.…”

Section: Wavefield Inversion Of Field Datamentioning

confidence: 99%

Imaging of intrabasalt and subbasalt structure with full wavefield seismic tomography

2006

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[1] The imaging of subsurface structure using conventional seismic reflection methods is problematic across areas where high-velocity basaltic rocks are intercalated with sedimentary layers of low velocity. In this study we use an approach that combines wavefield inversion of both normal-incidence and wide-aperture seismic data to constrain velocity structure within and beneath the basalt. Our field data are a two-ship long-offset profile acquired in the Faeroe Basin. A conventional traveltime inversion of the wideangle data is performed to obtain a starting model for the wavefield inversion. Synthetic tests are used to explore resolution and to determine a strategy for inversion of the field data. Our final velocity model shows a high-velocity basaltic layer underlain by an intermediate-velocity layer that is presumably sedimentary. The basalts appear highly heterogeneous in velocity, and the degree of heterogeneity increases significantly with depth within the layer. A prestack depth migration, using the final velocity model, reveals a number of new features. Despite the velocity heterogeneity within the basalts, strong reflections are seen within and immediately beneath the basaltic section, and these reflectors are more clearly imaged on the final depth-migrated section than hitherto. The transition from sediments to basalt does not appear to be sharp, uniquely defined, or locally subhorizontal. The data suggest that velocity heterogeneity, and the complexity of the transition from basalt to sediment, may explain the difficulties of imaging beneath basalts west of Britain. Wavefield tomography can resolve this complexity and hence improve both imaging and confidence of interpretation within and beneath basalts.

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Section: Wavefield Inversion Of Field Datamentioning

confidence: 99%

Imaging of intrabasalt and subbasalt structure with full wavefield seismic tomography

2006

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“…A seismic upper crustal layer can be mapped regionally based on its relatively high velocity gradient, but the base of this layer probably represents an alteration front rather than the base of the extrusive layer [ Flovenz and Gunnarsson , 1991; Darbyshire et al , 2000a]. Smallwood et al [1998] noted a sequence of dipping reflections down to 15 km on a deep seismic reflection profile shot along Reydarfjödur on the eastern Iceland Shelf. It is unclear how much of this reflective sequence is composed of lava flows.…”

Section: Observationsmentioning

confidence: 99%

“…Onshore region is based on data compilation of Darbyshire et al [2000a]. Eastern and western offshore shelves are constrained by refraction profiles of Smallwood et al [1998] and Holbrook et al [2001]. Northern and southern shelf regions are determined by calculating crustal thickness required to counteract plate cooling and maintain a shelf top as a plateau assuming Airy isostasy.…”

Section: Introductionmentioning

confidence: 99%

Crustal flow beneath Iceland

Jones

Maclennan

2005

J. Geophys. Res.

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[1] Theoretical and experimental studies indicate that when oceanic crust is hotter than about 800°C, variations in crustal thickness drive lower crustal flow. We investigate the nature of crustal flow beneath Iceland, where zero-age crust varies in thickness from under 20 km to over 40 km over a distance of 100 km and temperatures exceed 1000°C below depths of a few kilometers. We model the regional characteristics of crustal flow using the two-dimensional channel flow equation with depth-dependent viscosity. The model predicts the observed decay in crustal thickness contrasts between zero-age and off-axis crust on shore Iceland and development of a sharp Moho step as the plate moves away from the rift axis. These features become locked in place as plate cooling increases the viscosity. Observations are best matched by model predictions when the solidus viscosity is of order 10 18 Pa s, in agreement with viscosity estimates from deformation rates associated with deglaciation and plate boundary processes. Crustal flow acts to erase the crustal thickness memory of ridge-plume interaction, so that maps of Icelandic crustal thickness can be used neither to derive a detailed plume flux history nor to test in detail whether the Iceland Plume center is fixed relative to other hot spots. Crustal flow beneath Iceland is an unusually clear example of the kind of flow postulated to explain continental phenomena including exhumation of metamorphic core complexes and associated development of low-angle detachments within extensional terrains and sharp-edged plateau topography in major collisional belts.

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“…Planke and Eldholm 1994;Smallwood, White and Staples 1998). Planke and Eldholm 1994;Smallwood, White and Staples 1998).…”

Section: P R O B L E M S I N I M a G I N G T H R O U G H B A S A Lt Smentioning

confidence: 99%

Imaging and regional distribution of basalt flows in the Faeroe‐Shetland Basin

White

Smallwood²,

Fliedner

et al. 2003

Geophysical Prospecting

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We demonstrate that the use of long‐offset seismic data allows wide‐angle reflections and diving waves to be recorded, and that these can be used in conjunction with prestack depth migrations to constrain and to image the base of the basalt flows and the underlying structure in the Faeroe‐Shetland Basin. Crustal velocity models are built first by inverting the traveltimes of the recorded reflections and diving waves using ray‐tracing methods. Finer details of the velocity structure can then be refined by analysis of the amplitudes and waveforms of the arrivals. We show that prestack depth migration of selected wide‐angle arrivals of known origin, such as the base‐basalt reflection, using the crustal velocity model, allows us to build a composite image of the structure down to the pre‐rift basement. This has the advantage that the wide‐angle first‐arriving energy must be primary, and not from one of the many multiples or mode‐converted phases that plague near‐offset seismic data. This allows us to ‘tag’ these primary arrivals with confidence and then to identify the same arrivals on higher‐resolution prestack migrations that include data from all offsets. Examples are drawn from the Faeroe‐Shetland Basin, with a series of regional maps of the entire area showing the basalt depths and the thickness of the basalt flows and underlying sediment down to the top of the pre‐rift basement. The maps show how the basalts thin to the southeast away from their presumed source west of the present Faeroe Islands, and also show the extent to which the structure of the pre‐rift basement controls the considerable variations in sediment thickness between the basement and the cap formed by the overlying basalt flows.

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Deep crustal reflectors under Reydarfjördur, eastern Iceland:crustal accretion above the Iceland mantle plume

Cited by 34 publications

References 42 publications

Imaging of intrabasalt and subbasalt structure with full wavefield seismic tomography

Imaging of intrabasalt and subbasalt structure with full wavefield seismic tomography

Crustal flow beneath Iceland

Imaging and regional distribution of basalt flows in the Faeroe‐Shetland Basin

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