Deep crustal seismic reflection profiling across two major tectonic zones in southern Sweden

Dahl‐Jensen, Trine; Dyrelius, Dan; Palm, Hans

doi:10.1016/0040-1951(91)90211-a

Cited by 19 publications

(8 citation statements)

References 23 publications

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“…This indicates that environmental noise may have affected the small‐charge data from southwestern Sweden. Comparison of the deep component Luleå data with 25–50 kg charges in southwestern Sweden (Dahl‐Jensen et al 1991) shows the amplitude curves to be quite similar, except for the increased values at 12–14 s in the Luleå data that correspond to lower crustal reflectivity. This is a strong indication that the weak or absent lower crustal reflectivity in the TIB rocks is a result of geological factors (when the charge size is over 10 kg) as suggested by other authors (Hurich 1996; Juhojuntti et al 2001).…”

Section: Discussionmentioning

confidence: 93%

“…Previously acquired deep seismic onshore profiles in Sweden generally show only weak reflectivity in the lower crust (Dahl‐Jensen et al 1991; Juhojuntti & Juhlin 1998; Juhojuntti et al 2001). The lack of strong reflectivity has been attributed to the fact that the profiles were mainly acquired over the Trans‐Scandinavian Igneous Belt, a large batholith, that has undergone only minor deformation since emplacement (Hurich 1996; Juhojuntti et al 2001).…”

Section: Discussionmentioning

confidence: 99%

“…Average background noise level from the shallow component data is shown as a horizontal very thin black line. Shown also are the amplitude decay curves from studies in southwestern Sweden for charges of 0.5–1 kg (Juhlin et al 2000) and charges of 25–50 kg (Dahl‐Jensen et al 1991). The 0.5–1 kg curve (thin black line) was amplitude normalized prior to the first arrival and shifted 8 dB for the peak to coincide with the small‐charge Luleå data.…”

Section: Discussionmentioning

confidence: 99%

“…Imaging of the reflective lower crust was another important component of the project since many of the deep seismic profiles acquired on land in Sweden show poor lower crustal reflectivity (e.g. Dahl‐Jensen et al 1991; Juhojuntti & Juhlin 1998; Juhojuntti et al 2001). If the well‐defined lower crustal reflectivity below the Bothnian Bay was also observed on the test profile then the lack of lower crustal reflectivity elsewhere could possibly be attributed to geological factors and not necessarily to acquisition methods.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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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“…Residual statics were found to be minimal for P-wave arrivals, but significant for S-wave events. Earlier work revealed residual statics to be a common problem when surveying Precambrian shield areas using on-land deep-seismic methods (Juhlin 1990;Dahl-Jensen, Dyrelius & Palm 1991). due to large lateral variation in near-surface velocities.…”

Section: P R O C E S S I N G T H E Pre-critical D a T Amentioning

confidence: 99%

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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Kinematics of a major fan-like structure in the eastern part of the Sveconorwegian orogen, Baltic Shield, south-central Sweden

Wahlgren

Cruden

Stephens

1994

Precambrian Research

116

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Deep crustal seismic reflection profiling across two major tectonic zones in southern Sweden

Cited by 19 publications

References 23 publications

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

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

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

Kinematics of a major fan-like structure in the eastern part of the Sveconorwegian orogen, Baltic Shield, south-central Sweden

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