Delineation and character of the Archaean-Proterozoic boundary in northern Sweden

Öhlander, Björn; Skiöld, Torbjörn; Elming, Sten-åke; Claesson, Stefan; Nisca, Dan H.

doi:10.1016/0301-9268(93)90069-e

Cited by 71 publications

(28 citation statements)

References 33 publications

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“…the Alps and the Pyrenees) and Palaeozoic (the Caledonides and the Appalachians) orogens, these mantle reflectors are interpreted as relics of Proterozoic (0.9-1.2 Ga and 1.8-1.9 Ga) tectonic processes related to Svecofennian and Sveconorwegian plate convergence, subduction and accretion of terranes onto the Archaean nucleus of the Baltic Shield (BABEL Working Group 1990Group , 1993b. This tectonic interpretation is supported by Sm-Nd isotopic data from the exposed volcanic arc complex in the Baltic Shield (Ohlander et al 1993). Recent analysis of lithospheric-scale seismic data from 1.90-1.85 Ga subduction zones at the Slave and Baltic cratonic margins (Snyder 2002) reveals strong similarity between them and modern tectonic analogues.…”

Section: Baltic Shieldmentioning

confidence: 86%

Deep Europe today: geophysical synthesis of the upper mantle structure and lithospheric processes over 3.5 Ga

Artemieva

Thybo

Kaban

2006

Memoirs

103

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We present a summary of geophysical models of the subcrustal lithosphere of Europe. This includes the results from seismic (reflection and refraction profiles, P-and S-wave tomography, mantle anisotropy), gravity, thermal, electromagnetic, elastic and petrological studies of the lithospheric mantle. We discuss major tectonic processes as reflected in the lithospheric structure of Europe, from Precambrian terrane accretion and subduction to Phanerozoic rifting, volcanism, subduction and continent-continent collision. The differences in the lithospheric structure of Precambrian and Phanerozoic Europe, as illustrated by a comparative analysis of different geophysical data, are shown to have both a compositional and a thermal origin. We propose an integrated model of physical properties of the European subcrustal lithosphere, with emphasis on the depth intervals around 150 and 250 km. At these depths, seismic velocity models, constrained by body-and surface-wave continent-scale tomography, are compared with mantle temperatures and mantle gravity anomalies. This comparison provides a framework for discussion of the physical or chemical origin of the major lithospheric anomalies and their relation to large-scale tectonic processes, which have formed the present lithosphere of Europe.

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Section: Baltic Shieldmentioning

confidence: 86%

Deep Europe today: geophysical synthesis of the upper mantle structure and lithospheric processes over 3.5 Ga

Artemieva

Thybo

Kaban

2006

Memoirs

103

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“…To the SW of this inferred border line there is no Archean basement present, only juvenile Proterozoic material, which was thus added to an older crust at an active continental margin (Huhma 1986;Vaasjoki and Sakko 1988). The more precise site of this border is, however, not well known, but on the basis of Sm-Nd and geophysical data it is possible to show that the Archean paleoboundary is situated ca 100 km north of the Skellefte district running WNW between Lulegt and Jokkmokk (Ski61d and Ohlander 1989;Ohlander et al 1993).…”

Section: Sulphur Isotopes and Metaliogenetic Evolution Of Northern Fementioning

confidence: 98%

Sulphur isotopes in Lower Proterozoic iron and sulphide ores in northern Sweden

1995

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Abstract. The present investigation deals with sulphur isotope distribution in Lower Proterozoic iron and sulphide mineralizations in northern Sweden. The contrastmg sulphur isotope patterns are indicative of different genesis. Some 267 sulphur isotope analyses of pyrite, pyrrhotite, chalcopyrite, sphalerite, galena and bornite from 23 occurrences have been performed. Some deposits exhibit uniform compositions, although the mean 634S values are clearly different, while other mineralizations have widely fluctuating values.The 634S values in syngenetic, exhalative sedimentary skarn iron ores, quartz-banded iron ores and sulphide mineralizations of the 2.0-2.5 Ga old (Lapponian) Greenstone group show a large spread, supporting the existence of bacteriogenic sulphate reduction processes. The spread of the sulphur isotope values (&34S = -8 to + 25%o), and the non-equilibrium conditions, point to a biogenic rather than to an inorganic reduction of seawater sulphate.The isotopic composition of the sulphides in the epigenetic Lannavaara iron ores which were formed by a hydrothermal scapolite-tourmaline-related process, indicates a sulphur source similar to that of the Greenstone group. The &34S values of Cu-(Au) sulphide mineralizations in the Malmberget region (e.g. Aitik), which were formed by a similar process and hosted by the volcanicsvolcanoclastics of the 1.9Ga old Porphyry group, are slightly below zero %0, indicating a magmatic origin. The existence of different sulphur compositions for these mineralization types formed by a similar hydrothermal process, probably reflects the influence of the host rock, the solutions leaching pre-existing sulphides.In southern Norrbotten, epigenetic, Cu-Zn-Pb veintype mineralizations in metavolcanics and metasediments have 634S values close to zero %0 indicating a magmatic origin. The sulphur isotope data of the volcanogenic, massive sulphide ores of the Skellefte district, in particular the ores of the Adak dome, are close to zero %0.The lead and sulphur isotopic features of the sulphides in northern Sweden show that the ore-forming processes were of a different nature on both sides of the ArcheanProterozoic border, implying differences in the crustal development. Lead isotopes show that lead was mobilized from specific sources on each side of the border. The sulphur of the sulphides in the Greenstone group in NE Sweden and Finland was introduced by sedimentary processes, whereas the sulphur of the sulphide occurrences towards the SW, mainly in the Porphyry group, is dominated by a magmatic sulphur component.

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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%

“… Interpretation of BABEL Line 3/4 seismic data in the Bothnian Bay based on Öhlander et al (1993) and BABEL Working Group (1993). The distance scale refers to the distance along the profile as shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

“…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. Finally, the seismic test profile would also cross a major break in the magnetic anomaly pattern that may represent a Proterozoic southwest‐dipping thrust zone (Lilljequist 1980; Öhlander et al 1993). In order to image both upper crustal and lower crustal features the seismic test profile consisted of a small‐charge higher‐resolution shallow component and a larger‐charge lower‐resolution deep component.…”

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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Delineation and character of the Archaean-Proterozoic boundary in northern Sweden

Cited by 71 publications

References 33 publications

Deep Europe today: geophysical synthesis of the upper mantle structure and lithospheric processes over 3.5 Ga

Deep Europe today: geophysical synthesis of the upper mantle structure and lithospheric processes over 3.5 Ga

Sulphur isotopes in Lower Proterozoic iron and sulphide ores in northern Sweden

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

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