Migratory tectonic switching, western Svecofennian orogen, central Sweden: Constraints from U/Pb zircon and titanite geochronology

Hermansson, Tobias; Stephens, Michael B.; Corfú, Fernando; Page, Laurence; Andersson, Jenny

doi:10.1016/j.precamres.2007.08.008

Cited by 85 publications

(75 citation statements)

References 48 publications

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“…This is in accordance with microstructural results suggesting periods of metamorphic mineral growth temporally close to the D 2 transpressive deformational event in the hydrothermally altered zone at Falun (Kampmann et al, 2016). In contrast to the results of this study, U-Pb (zircon and titanite) and 40 Ar-39 Ar (hornblende) geochronology indicate the greater significance of the earlier M 1 event around 1.86 Ga in at least the north-eastern part of the Bergslagen lithotectonic unit, involving penetrative ductile deformation and peak metamorphism under amphibolite facies conditions (Hermansson et al, 2007(Hermansson et al, , 2008a. More work is required to shed more light on the variation in the timing of peak metamorphism inside the Bergslagen lithotectonic unit.…”

Section: Timing Of Monazite Growth In a Regional Metamorphic Contextcontrasting

confidence: 85%

“…1) in the Fennoscandian Shield, Sweden. Orogenic activity in this lithotectonic unit was dominated by separate tectonic cycles, the more significant ones occurring during the time intervals 1.91-1.86 Ga and 1.86-1.82 Ga (Hermansson et al, 2008a;Stephens et al, 2009;Stephens and Andersson, 2015). The tectonic setting during each cycle involved a shift between retreating and advancing arc modes along a convergent active continental margin, transtension occurred in the retreating mode throughout the larger part of each cycle.…”

Section: Regional Geological Settingmentioning

confidence: 91%

“…The tectonic setting during each cycle involved a shift between retreating and advancing arc modes along a convergent active continental margin, transtension occurred in the retreating mode throughout the larger part of each cycle. Each transtensional stage was followed by shorter periods of transpression (D 1 and D 2 , respectively) in the advancing mode, around 1.87-1.86 Ga and 1.84-1.82 Ga (Hermansson et al, 2007(Hermansson et al, , 2008aStephens et al, 2009;Beunk and Kuipers, 2012;Stephens and Andersson, 2015). This orogenic development resulted in polyphase deformation and metamorphism under low-P, greenschist-to amphiboliteand locally granulite-facies conditions (Stephens et al, 2009).…”

Section: Regional Geological Settingmentioning

confidence: 99%

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Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U–Pb geochronology on zircon and monazite

Kampmann

Stephens

Ripa

et al. 2016

Precambrian Research

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a b s t r a c t U-Th-Pb (zircon and monazite) ion probe data have provided constraints on the timing of emplacement and metamorphism of magmatic rocks close to the Palaeoproterozoic, Falun base metal sulphide deposit in the Bergslagen lithotectonic unit, Fennoscandian Shield, Sweden, and, thereby the timing of mineralisation. Hydrothermal alteration and mineralisation at Falun are constrained to a short interval of several million years between a 207 Pb/ 206 Pb weighted average age of 1894 ± 3 Ma for a rhyolitic sub-volcanic rock in the felsic volcanic to sub-volcanic host rock suite, and a 207 Pb/ 206 Pb weighted average age of 1891 ± 3 Ma for a post-sulphide, porphyritic dacite dyke. Magmatism also included the emplacement of granite plutons with igneous crystallization ages of 1894 ± 3, 1894 ± 2 Ma and 1893 ± 3 Ma. The felsic sub-volcanic to volcanic activity and the emplacement of dacite dykes and granite plutons overlap in age within their respective analytical uncertainties, indicating hydrothermal alteration and sulphide mineralisation inside a narrow time span of intense magmatic activity, and burial of the supracrustal rocks. Two distinct patchy and homogeneous metamorphic monazite types in a felsic volcanic rock around and hydrothermally altered rocks at the Falun deposit yield 207 Pb/ 206 Pb weighted average ages of 1831 ± 8 Ma and 1822 ± 5 Ma, respectively. These ages fall well within the temporal range of a younger 1.84-1.81 Ga (M 2 ) metamorphic episode during the 2.0-1.8 Ga Svecokarelian orogeny, with the older episode (M 1 ) inside the Bergslagen lithotectonic unit at around 1.86 Ga. This shows the major influence of the M 2 event in the north-western part of this unit, leading to a complete resetting of the U-Th-Pb isotope system in monazite.

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Section: Timing Of Monazite Growth In a Regional Metamorphic Contextcontrasting

confidence: 85%

Section: Regional Geological Settingmentioning

confidence: 91%

Section: Regional Geological Settingmentioning

confidence: 99%

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Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U–Pb geochronology on zircon and monazite

Kampmann

Stephens

Ripa

et al. 2016

Precambrian Research

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“…Triassic and Jurassic extension and formation of a back-arc basin in the North American Cordilleran was followed by basin inversion and thrusting, leading to island arc accretion through Nevada and California (Dickinson, 2006). Tectonic switching and back-arc basin closure has been used to explain the accretion of terranes in the Lachlan orogen in Australia (Collins, 2002) and the Svecofennian orogen in Sweden (Hermansson et al, 2008).…”

Section: J L Tetreault and S J H Buiter: Future Accreted Terranesmentioning

confidence: 99%

Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

Tetreault

Buiter

2014

Solid Earth

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Abstract. Allochthonous accreted terranes are exotic geologic units that originated from anomalous crustal regions on a subducting oceanic plate and were transferred to the overriding plate by accretionary processes during subduction. The geographical regions that eventually become accreted allochthonous terranes include island arcs, oceanic plateaus, submarine ridges, seamounts, continental fragments, and microcontinents. These future allochthonous terranes (FATs) contribute to continental crustal growth, subduction dynamics, and crustal recycling in the mantle. We present a review of modern FATs and their accreted counterparts based on available geological, seismic, and gravity studies and discuss their crustal structure, geological origin, and bulk crustal density. Island arcs have an average crustal thickness of 26 km, average bulk crustal density of 2.79 g cm −3 , and three distinct crustal units overlying a crust-mantle transition zone. Oceanic plateaus and submarine ridges have an average crustal thickness of 21 km and average bulk crustal density of 2.84 g cm −3 . Continental fragments presently on the ocean floor have an average crustal thickness of 25 km and bulk crustal density of 2.81 g cm −3 . Accreted allochthonous terranes can be compared to these crustal compilations to better understand which units of crust are accreted or subducted. In general, most accreted terranes are thin crustal units sheared off of FATs and added onto the accretionary prism, with thicknesses on the order of hundreds of meters to a few kilometers. However, many island arcs, oceanic plateaus, and submarine ridges were sheared off in the subduction interface and underplated onto the overlying continent. Other times we find evidence of terrane-continent collision leaving behind accreted terranes 25-40 km thick. We posit that rheologically weak crustal layers or shear zones that were formed when the FATs were produced can be activated as detachments during subduction, allowing parts of the FAT crust to accrete and others to subduct. In many modern FATs on the ocean floor, a sub-crustal layer of high seismic velocities, interpreted as ultramafic material, could serve as a detachment or delaminate during subduction.

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“…In the first semi-continuous, protracted accretion of island arcs to the Archean craton led to southwestward growth of the orogenic belt (Gorbatchev and Bogdanova 1993); in a refinement of this model continuous long-lived subduction occurred with repeated retreating and advancing stages (Hermansson et al, 2008;Stephens and Andersson, 2015). The second model involves accretion of microcontinents (Nironen, 1997), and the orogeny consisted of separate orogenic stages, including microcontinent accretion (1.92-1.87 Ga), continental extension (1.86-1.84 Ga), continental collision (1.84-1.79 Ga), and finally orogenic collapse and stabilization (1.79-1.77 Ga: Lahtinen et al, 2005).…”

Section: Geological Settingmentioning

confidence: 99%

The Salittu Formation in southwestern Finland, part I: Structure, age and stratigraphy

Nironen¹,

Mänttäri²,

Väisänen³

2016

Bull Geol Soc Finland

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Because of the relatively low metamorphic grade, low strain and well-preserved early structures in volcanic and volcaniclastic rocks, the Orijärvi triangle (in the center of the larger Orijärvi area) is one of the few locations in the Svecofennian orogen of southern Finland where lithostratigraphy has been determined. The geochemistry of the picriticbasaltic metavolcanic rocks of the Salittu Formation, located in the northeastern part of the Orijärvi area, has been characterized but otherwise the bedrock and structures have been barely touched. After remapping we give an interpretation of structural evolution, provide new age data to constrain duration of volcanism at Salittu, and refine the stratigraphy in the Orijärvi area.The original stratigraphy is visible at Salittu: metabasalt overlies migmatitic gneisses, and metapicrite is on top. The rocks were folded during early Svecofennian D 1 -D 2 deformations, and the large synformal structures developed as D 2 -D 5 interference structures formed during late Svecofennian D 5 deformation. The structural pattern at Salittu is much the same as in the Orijärvi triangle.The new age data, combined with earlier published data, constrains the Salittu volcanism at ca. 1875 Ma. The stratigraphy in the Orijärvi area consists of the early (1.90-1.89 Ga) volcanic Orijärvi Formation, overlain by the sedimentary Vetio Formation, the volcanic Kisko Formation, the volcanic-sedimentary Ahdisto Formation, the volcanic Toija Formation, and on top the Salittu Formation, all emplaced at 1.88-1.87 Ga. We propose a model in which the Orijärvi Formation represents magmatism at the margin of a microcontinent, and the overlying package represents sedimentation and magmatism above a subduction zone during an initial stage of microcontinental accretion. D 1 deformation occurred in an advanced stage of accretion, after emplacement of the volcanic rocks of the Salittu Formation.

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Migratory tectonic switching, western Svecofennian orogen, central Sweden: Constraints from U/Pb zircon and titanite geochronology

Cited by 85 publications

References 48 publications

Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U–Pb geochronology on zircon and monazite

Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U–Pb geochronology on zircon and monazite

Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

The Salittu Formation in southwestern Finland, part I: Structure, age and stratigraphy

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