Pre-critical wide-angle reflections from the Baltic shield: evidence for a 1.8 Ga subduction complex

Lindsey, G.; Snyder, David B.

doi:10.1016/0040-1951(94)90083-3

Cited by 8 publications

(11 citation statements)

References 22 publications

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“…Although observed S-wave reflections from depths greater than 15 km and P-S conversions at the top of the reflecting zone have simiiar arrival times to the modelled P-wave arrivals, modelling shows that their lower apparent velocity across the gather easily distinguishes them from primary P reflections. The reflections modelled beneath station 202 (Lindsey & Snyder 1994) are similar to those described here for station 602. Reflective zones within the crust of the Baltic shield appear to have numerous discrete layers of anomalous velocity and density: most reflectors within one part of the crust have similar dip with some cross-cutting relationships.…”

Section: Results Of Combined Stacksmentioning

confidence: 84%

“…Lindsey & Snyder 1994). By presenting such data sets as summed receiver gathers to increase the signal-to-noise ratio, or as interleaved receiver gathers to enhance lateral resolution, they can be used as the basis for very detailed crustal modelling.…”

Section: Discussion a N D Conclusionmentioning

confidence: 99%

“…This results in a very densely spaced single-fold receiver gather (Fig. 3c;Lindsey & Snyder 1994), with average trace spacing as little as 4 m and the elimination of gaps due to tape changes seen in the single-fold receiver gathers. With such a high degree of lateral resolution, confidence in tracing arrivals laterally is considerably increased and spatial aliasing reduced.…”

Section: Stacked and Interleaved Receiver Gathersmentioning

confidence: 93%

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Processing of pre-critical wide-angle seismic reflection data from the BABEL project

Dahl‐Jensen¹,

Lindsey²,

Law³

et al. 1995

Geophysical Journal International

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S U M M A R YIn addition to using the now widely recognised technique of simultaneously acquiring deep reflection profiles at sea and long-range refraction profiles using three-component land stations, the BABEL seismic experiment also recorded Pand S-wave energy from the large airgun array at four linear 38-component land spreads. The pioneering nature of this work led, in hindsight, to several deficiences in design, but also pointed the way towards substantial advances in analysis and interpretation of integrated seismic observations. The multifold nature of the recordings at offsets providing pre-critical reflections from Moho depths resulted in interleaved receiver gathers with trace spacings of 4-5 m, thus providing some of the most densely spaced deep-seismic wide-angle sections to date. With such a trace density, the signal-to-noise ratio was substantially increased by summation of adjacent traces, without degrading spatial resolution. Stacking the land array data using conventional common midpoint (CMP) gather techniques over sourcereceiver offsets of 7-78 km doubled the depth range constrained by numerically precise stacking velocity analysis. Offsets > 10 km provide normal moveouts > 1 s, although the 1.5 km of differential moveout available here limited velocity discrimination and required additional constraints to define zero-offset traveltimes. For one array, stacking velocity errors of *200ms-' imposed a resulting error in zero-offset time of up to k400ms without use of any marine data. With receiver response functions matched, stacked sections using data from geophone arrays exhibit similar features to stacks made using hydrophone arrays at 0-3 km offsets in the same area, but also significant differences. The differences in reflection amplitudes cannot be simply attributed to theoretical amplitude-offset variations and probably represent variation in the reflectivity of the crustal rocks of the Baltic shield.

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Section: Results Of Combined Stacksmentioning

confidence: 84%

Section: Discussion a N D Conclusionmentioning

confidence: 99%

Section: Stacked and Interleaved Receiver Gathersmentioning

confidence: 93%

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Processing of pre-critical wide-angle seismic reflection data from the BABEL project

Dahl‐Jensen¹,

Lindsey²,

Law³

et al. 1995

Geophysical Journal International

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“…4), occurs about 50 km to the south and may represent a layer within the subducted slab or possibly a second, younger subduction zone. Modelling of reflection data just southwest of this mantle reflection indicates thin (c. 100 m) layers of alternating high and low velocity rocks in the lower crust (Lindsey & Snyder 1994). These layers were interpreted as either underthrust oceanic crust and sediments within a subduction zone or as cumulate layering at the base of an arc.…”

Section: Archaean-proterozoic Crustal Boundarymentioning

confidence: 96%

Crustal and mantle reflectors from Palaeoproterozoic orogens and their relation to arc-continent collisions

Snyder¹,

Lucas

McBride³

1996

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“…Published interpretations of the BABEL surveys in the Bothnian Bay (BABEL Working Group 1990; Öhlander et al 1993; Lindsey & Snyder 1994; Gohl & Pedersen 1995) generally indicate reflective Archaean crust overlain by transparent crust. This transparent crust has been interpreted as reworked Archaean rocks (Fig.…”

Section: Introductionmentioning

confidence: 99%

Crustal reflectivity near the Archaean-Proterozoic boundary in northern Sweden and implications for the tectonic evolution of the area

Juhlin¹,

Elming

Mellqvist³

et al. 2002

Geophysical Journal International

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Summary Sm–Nd isotope ratios of 1.9–1.8 Ga granitoids delineate the Archaean–Proterozoic boundary in northern Sweden, an important feature in the Fennoscandian Shield. The boundary strikes approximately WNW–ESE and is defined as a c. 20 km wide zone with juvenile Palaeoproterozoic rocks to the SSW and Archaean and Proterozoic rocks, derived to a large extent from Archaean sources, to the NNE. It therefore constitutes the strongly reworked margin of the old Archaean craton. Extrapolation of the boundary offshore into the Bothnian Bay and correlation with the marine reflection seismic BABEL Lines 2 and 3/4 indicates that the boundary dips to the south‐southwest, consistent with interpretation of the Sm–Nd data. In order to tie the BABEL results with onshore surface geology and obtain detailed images of the uppermost crust a short (30 km of subsurface coverage) pilot profile was acquired in the Luleå area of northern Sweden during August 1999. The profile consisted of a high‐resolution shallow component (1 kg shots) and a lower‐resolution deep component (12 kg shots). Both components image most of the reflective crust, with the deep component providing a better image below 10 s. Comparison of signal penetration curves with data acquired over the Trans‐Scandinavian Igneous Belt (a large batholith) indicate the transparent nature of the crust there to be caused by geological factors, not acquisition parameters. Lower crustal reflectivity patterns on the Luleå test profile are similar to those observed on the BABEL lines, suggesting the same lower crust onshore as offshore. Interpreted Archaean reflective upper crust in the NE extends below more transparent Proterozoic crust in the SW. This transparent crust contains a number of high‐amplitude reflectors that may represent shear zones and/or mafic rock within granite intrusions. A marked boundary in the magnetic field in the SW has been interpreted as being the result of a gently west‐dipping contact zone between meta‐sediments and felsic volcanic rocks, however, the seismic data indicate a near‐vertical structure in this area. By correlating the onshore and offshore seismic data we have better defined the location of the Archaean–Proterozoic boundary on the BABEL profiles. Our new interpretation of the crustal structure along the northern part of the BABEL Line 2 shows a more bi‐vergent geometry than previous interpretations. Comparison of the re‐interpreted crustal structure in northern Sweden with that found in the Middle Urals shows several similarities, in particular the accretion of a series of arcs to a stable craton. Based on this similarity and geological data, we deduce that a continental arc accreted to the southwestern margin of the Archaean craton at c. 1.87 Ga. Shortly thereafter, the Skellefte island arc underthrust the continental arc owing to a collision further to the southwest resulting in the bi‐vergent crustal structure observed today.

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Pre-critical wide-angle reflections from the Baltic shield: evidence for a 1.8 Ga subduction complex

Cited by 8 publications

References 22 publications

Processing of pre-critical wide-angle seismic reflection data from the BABEL project

Processing of pre-critical wide-angle seismic reflection data from the BABEL project

Crustal and mantle reflectors from Palaeoproterozoic orogens and their relation to arc-continent collisions

Crustal reflectivity near the Archaean-Proterozoic boundary in northern Sweden and implications for the tectonic evolution of the area

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