Lateral variations in supracrustal geology within the swedish part of the southern svecokarelian volcanic belt

Lundström, Ingmar

doi:10.1016/0301-9268(87)90063-5

Cited by 31 publications

(10 citation statements)

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“…Variable proportions of Early Proterozoic and Archaean detrital zircons have been recorded in these sedimentary successions (Claesson et al 1993) indicating a proximity to a pre-Svecofennian continental provenance area. The meta-sediments are relatively rare in the interior parts of Bergslagen but are more abundant when approaching the Baltic Sea (Lundstr6m 1987). The crustal maturity of the volcanic and sedimentary components in Bergslagen have been evaluated by Sm-Nd systematics (Patchett et al 1987;Valbracht 1991;Bj6rklund and Claesson 1992;Sundblad et al 1993a).…”

Section: Svecofennian and Post-svecofennian Crustal Evolutionmentioning

confidence: 99%

A genetic reinterpretation of the Falun and �mmeberg ore types, Bergslagen, Sweden

Sundblad

1994

Mineral. Deposita

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The stratiform sulphide and oxide ores of Bergslagen, south-central Sweden, constitute the largest concentration of base metal and iron ores in northern Europe. They are hosted by Early Proterozoic metamorphosed volcanic and sedimentary successions, which (together with later granitoids) belong to the Svecofennian Domain. An earlier genetic model suggested that two principal PeS of sulphide ores existed in Bergslagen (Falun and meberg), which had been formed through two contrasting granitoid-related processes, whereas the iron oxide ores were considered exhalative-volcanogenic. The prevailing view for the Bergslagen ores is that all stratiform sulphide (and oxide) ores were formed by exhalative-volcanogenic processes from one homogenous metal source. In this paper are presented new high-precision determinations of the ore lead isotopic composition of twentytwo stratiform sulphide and oxide ores in Bergslagen (among them Falun, Zinkgruvan-/~mmeberg and Dannemora), in order to provide an improved base for their genesis. The results show that significant variations in metal sources existed in Bergslagen for the volcanogenic ores. Most ores (including the Falun Cu-Zn-Pb deposit) were formed from a major isotopic reservoir that occurs in the interior parts of Bergslagen. This source is defined as the Falun reservoir and is dominated by calcalkaline felsic volcanic rocks. A variable input from a more evolved source component (recycled pre-Svecofennian crustal components) is locally important in sedimentdominated areas, particularly the Stockholm archipelago. A third source, representing relatively primitive meta-

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Section: Svecofennian and Post-svecofennian Crustal Evolutionmentioning

confidence: 99%

A genetic reinterpretation of the Falun and �mmeberg ore types, Bergslagen, Sweden

Sundblad

1994

Mineral. Deposita

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“…layers of basal greywackes suggest an original continental margin (Lundstrom 1987). Archaean components found in Proterozoic granites of the NSP suggest an underlying Archaean crust (Patchett, Todt & Gorbatshev 1987;Park 1991).…”

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confidence: 99%

Collisional tectonics of the Baltic Shield in the northern Gulf of Bothnia from seismic data of the BABEL project

Gohl

Pedersen

1995

Geophysical Journal International

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SUMMARY Densely spaced wide‐angle data from stations recording airgun shots along BABEL profile 2 in the northern Gulf of Bothnia were analysed, modelled, and compared with the normal‐incidence recordings. Profile 2 extends from the metasedimentary and metavolcanic Proterozoic Central Svecofennian Province into the volcanic Northern Svecofennian Province of magmatic arc affinity and crosses the Proterozoic‐Archaean boundary of the northern Baltic Shield as defined from isotope studies. We used a 2‐D traveltime inversion to derive P‐ and S‐wave velocity‐depth models and a distribution of Poisson's ratios along the profile. A series of north‐dipping wide‐angle reflectors characterize the middle and lower crust in the southern part of the model, coinciding with similar events in previous multichannel wide‐angle data and the CMP recordings. Several subhorizontal upper to mid‐crustal wide‐angle reflectors and a well‐resolved Moho boundary at 42 to 45 km depth coincide with reflective zones or changes in reflectivity patterns of the CMP data. P‐wave velocities increase from 5.7 km s‐1 at the near‐surface to 6.4 and 6.6 km s‐1 in the mid‐crust and up to 7.6 km‐1 in the lowermost crust. Pn velocities reach 8.0 to 8.2 km s‐1 below the Moho in the northern part of the model but are less than 8.0 km s‐1 in the southern part. Poisson's ratios, calculated from the P‐ and S‐wave models, range from 0.21 to 0.25 in the uppermost crust to about 0.30 in the lower crust and upper mantle. Our velocity and Poisson's ratio models indicate that the upper crust contains predominantly felsic, quartz‐rich rocks. The increase of P‐wave velocity and Poisson's ratio in the mid‐ to lower crust is explained by increasingly mafic composition. We propose a geological model across the northern Gulf of Bothnia that combines our velocity‐depth model with results from the seismic normal‐incidence experiment, previous geophysical information, and geological surface observations. The model consists of a possibly multiple Proterozoic north‐dipping subduction zone with remnants of oceanic crust and zones of imbricated metasediments and mafics on top. There is evidence for a metasedimentary fore‐arc basin in the middle crust and a layer of mafic to ultramafic cumulates at the base or below parts of the lower crust. South‐dipping mid‐ and lower crustal zones of high reflectivity in the northern part of profile 2 indicate that Archaean crust underlies the Northern Svecofennian Province. The major features of this Proterozoic collision zone, such as the suggested subduction slab, zones of crustal reflectors dipping parallel to the slab, a metasedimentary basin, and mafic to ultramafic cumulates between the subduction slab and overlaying Moho, are well‐preserved analogues of recent oceaniccontinental collision and subduction zones.

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“…The volcanic 1358 succession is 1.5 km thick and overlies turbiditic 1359 metasediments in the east, and is over 7 km thick 1360 with no exposed base in the west (Lundströ m, 1987;1361Allen et al, 1996a. The basement is interpreted to be 1362 older, unexposed, continental crust.…”

mentioning

confidence: 99%

8: Precambrian geodynamics and ore formation: The Fennoscandian Shield

Weihed

Arndt

Billström

et al. 2005

Ore Geology Reviews

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15Compared with present-day global plate tectonics, Archaean and Palaeoproterozoic plate tectonics may have involved faster 16 moving, hotter plates that accumulated less sediment and contained a thinner section of lithospheric mantle. This scenario also 17 fits with the complex geodynamic evolution of the Fennoscandian Shield from 2.06 to 1.78 Ga when rapid accretion of island 18 arcs and several microcontinent-continent collisions in a complex array of orogens was manifested in short-lived but intense 19 orogenies involving voluminous magmatism. With a few exceptions, all major ore deposits formed in specific tectonic settings 20 between 2.06 and 1.78 Ga and thus a strong geodynamic control on ore deposit formation is suggested. 21All orogenic gold deposits formed syn-to post-peak metamorphism and their timing reflects the orogenic younging of the 22 shield towards the SW and west. Most orogenic gold deposits formed during periods of crustal shortening with peaks at 2.72 to 23 2.67, 1.90 to 1.86 and 1.85 to 1.79 Ga. 24The ca. 2.5 to 2.4 Ga Ni-Cu F PGE deposits formed both as part of layered igneous complexes and associated with mafic 25 volcanism, in basins formed during rifting of the Archaean craton at ca. 2.5 to 2.4 Ga. Svecokarelian ca. 1.89 to 1.88 Ga Ni-Cu 26 deposits are related to mafic-ultramafic rocks intruded along linear belts at the accretionary margins of microcratons. 27All major VMS deposits in the Fennoscandian Shield formed between 1.97 and 1.88 Ga, in extensional settings, prior to 28 basin inversion and accretion. The oldest bCyprus-typeQ deposits were obducted onto the Archaean continent during the onset of 29 convergence. The Pyhäsalmi VMS deposits formed at 1.93 to 1.91 Ga in primitive, bimodal arc complexes during extension of 30 the arc. In contrast, the Skellefte VMS deposits are 20 to 30 million years younger and formed in a strongly extensional intra-arc 31 region that developed on continental or mature arc crust. Deposits in the Bergslagen-Uusimaa belt are similar in age to the 32 Skellefte deposits and formed in a microcraton that collided with the Karelian craton at ca. 1.88 to 1.87 Ga. The Bergslagen- ARTICLE IN PRESS33 Uusimaa belt is interpreted as an intra-continental, or continental margin back-arc, extensional region developed on older 34 continental crust. 35Iron oxide-copper-gold (IOCG) deposits are diverse in style. At least the oldest mineralizing stages, at ca. 1.88 Ga, are 36 coeval with calc-alkaline to monzonitic magmatism and coeval and possibly cogenetic subaerial volcanism more akin to 37 continental arcs or to magmatic arcs inboard of the active subduction zone. Younger mineralization of similar style took place 38 when S-type magmatism occurred at ca. 1.80 to 1.77 Ga during cratonization distal to the active N-S-trending subduction zone 39 in the west. Possibly, interaction of magmatic fluids with evaporitic sequences in older rift sequences was important for ore 40 formation. 41Finally, the large volumes of anorthositic magmas that characterize the S...

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Lateral variations in supracrustal geology within the swedish part of the southern svecokarelian volcanic belt

Cited by 31 publications

References 20 publications

A genetic reinterpretation of the Falun and �mmeberg ore types, Bergslagen, Sweden

A genetic reinterpretation of the Falun and �mmeberg ore types, Bergslagen, Sweden

Collisional tectonics of the Baltic Shield in the northern Gulf of Bothnia from seismic data of the BABEL project

8: Precambrian geodynamics and ore formation: The Fennoscandian Shield

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