scholarly journals Deciphering the structural and metamorphic history of the Balsfjord Series in the Upper Allochthon of the Scandinavian Caledonides in northern Norway 

2021 ◽  
Author(s):  
Stephan Höpfl ◽  
Jiří Konopásek ◽  
Holger Stünitz ◽  
Steffen G. Bergh
Keyword(s):  
The Arctic ◽  
Low Grade ◽  
Prograde Metamorphism ◽  
Northern Norway ◽  
Metamorphic History ◽  
Scandinavian Caledonides ◽  
Nappe Complex ◽  
History Of ◽  
Peak Metamorphism ◽  
Metamorphic Gradient

<p>Deciphering the structural and metamorphic history of the Balsfjord Series in the Upper Allochthon of the Scandinavian Caledonides in northern Norway</p><p>Höpfl Stephan<sup>1</sup>, Konopásek Jiří<sup>1</sup>, Stünitz Holger<sup>1,2</sup> Bergh G., Steffen<sup>1</sup></p><p>UiT Norges arktiske universitet, Institutt for geovitenskap, [email protected]</p><p> </p><p><sup>1</sup>Department of Geosciences, UiT The Arctic University of Norway, Tromsø 9037, Norway</p><p><sup>2</sup>Institut des Sciences de la Terre (ISTO), Université d’Orleans, Orleans 45100, France</p><p> </p><p>The Balsfjord Series is located in the central part of Troms–Finnmark County, northern Norway, and is part of the upper allochthon of the Scandinavian Caledonides. It consists of an Ordovician–Silurian metsedimentary sequence lying on top of the mostly gabbroic Lyngen Magmatic Complex (LMC). The unit exhibits an inverted metamorphic gradient, where the metamorphic conditions increase from the base to the top, from very low grade in the southeast to medium grade in the west and northwest. The Balsfjord Series is sandwiched between two high-grade units, the Nakkedal + Tromsø Nappe Complex in the hanging wall and the Nordmannvik Nappe as the top part of the Reisa Nappe Complex (RNC) in the footwall. The Nakkedal + Tromsø Nappe Complex features metamorphic peak ages of ca. 455–450 Ma and the Nordmannvik Nappe of ca. 430 Ma. The peak metamorphism of the Balsfjord Series has never been dated and the role of the inverted metamorphic gradient is not yet understood. One of the main motivations in this project is to resolve the Caledonian deformation history in the Balsfjord Series, ideally leading to a regional tectonic model explaining the tectonostratigraphic and metamorphic relationships between the abovementioned units.</p><p>The Balsfjord Series features two main discernible folding phases. The earlier phase displays tight to isoclinal folds with flat lying axial surfaces parallel to the penetrative foliation. Observed fold axes are parallel with the stretching lineation. These folds are best preserved in the northwestern, upper part of the unit and are syn-metamorphic in certain areas, as they fold original bedding (transposed foliation). A later folding phase is represented by mainly open folds with inclined to steep axial surfaces. Their fold axes are gently plunging with a predominant NE–SW orientation. We interpret these two folding events to be genetically related but slightly diachronous. The earlier folding phase with flat lying axial surfaces was likely generated during nappe thrusting and peak metamorphism of the Balsfjord Series. The subsequent open folding with inclined to steep axial surfaces is explained as a result of continued shearing and shortening of the weaker metapelitic Balsfjord Series against the more rigid gabbroic part of the LMC during the late stages of the Caledonian nappe thrusting.      </p><p>Observed thrust kinematics and penetrative retrogression at the bottom of the Nakkedal + Tromsø Nappe Complex suggest that its final exhumation took place during prograde metamorphism of the underlying Balsfjord Series. The ongoing dating of the prograde metamorphism in the Balsfjord series will provide important information about a possible continuity between the timing of peak metamorphism in the Nakkedal + Tromsø Nappe Complex, the Balsfjord series and the underlying RNC.</p>

The subduction, exhumation, and deformation history of the Vaimok Lens, Seve Nappe Complex, Scandinavian Caledonides

2021 ◽  
Author(s):  
Christopher Barnes ◽  
Jarosław Majka ◽  
David Schneider ◽  
Mattia Gilio ◽  
Matteo Alvaro ◽  
...  
Keyword(s):  
Weighted Average ◽  
White Mica ◽  
Garnet Growth ◽  
Prograde Metamorphism ◽  
Early Ordovician ◽  
Metasedimentary Rocks ◽  
Scandinavian Caledonides ◽  
Nappe Complex ◽  
History Of ◽  
Seve Nappe Complex

<p>            The Seve Nappe Complex (SNC) of the Scandinavian Caledonides represents portions of the Baltican margin that were subducted to mantle depths. Eclogite-bearing sub-units of the SNC provide a record of this important step in orogen development. One such sub-unit is the Vaimok Lens of the SNC in southern Norrbotten. The Vaimok Lens constitutes eclogites hosted within metasedimentary rocks that reached ultra-high pressure (UHP) conditions in the Cambrian/Early Ordovician period. The metasedimentary rocks are typically composed of quartz, white mica, garnet, plagioclase, biotite, clinozoisite, apatite and titanite, and show a pervasive ‘S2’ foliation that developed during exhumation. Garnet is recognized as a relic of prograde metamorphism during subduction, whereas the other minerals represent retrogressive metamorphism during exhumation. To resolve the timing of prograde metamorphism, Lu-Hf geochronology was conducted on metasediment-hosted garnet that preserves prograde, bell-shaped Mn-zoning with a chemical formula of Alm<sub>69-59</sub>Grs<sub>32-24</sub>Sps<sub>13-2</sub>Prp<sub>5-2</sub>. The results indicate garnet growth at 495.3 ± 2.6 Ma. Quartz-in-garnet (QuiG) elastic geobarometry was also conducted on garnet from the same sample, providing pressures of 0.9-1.3 GPa, calculated at 500-700°C. Six samples were obtained for in-situ <sup>40</sup>Ar/<sup>39</sup>Ar geochronology, targeting white mica defining the S2 foliation. Samples can be classified as: 1) low-strain (n: 3), with large (>400 µm width), undeformed micas that are chemically homogeneous (X<sub>Cel</sub>: 0.24-0.35), which yielded a weighted average <sup>40</sup>Ar/<sup>39</sup>Ar population of 470.5 ± 5.9 Ma; 2) high-strain (n: 3), with small (<300 µm width) mica fish with heterogeneous chemistry (X<sub>Cel</sub>: 0.03-0.27), which provided weighted average <sup>40</sup>Ar/<sup>39</sup>Ar populations of 447.6 ± 2.6 Ma and 431.1 ± 4.1 Ma. An additional sample from the basal thrust of the lens that contains large (>300 µm width), homogeneous (X<sub>Cel</sub>: 0.24-0.34) mica was also dated, yielding a population of 414.1 ± 5.8 Ma. Altogether, the data indicates that the Vaimok Lens was subducting by c. 495 Ma. The lens underwent post-decompression cooling at c. 470 Ma, possibly decompressing to 0.9-1.3 GPa by this time. This would equate to an exhumation rate of 3-9 mm/yr. Imbrication of the SNC in southern Norrbotten is taken to be c. 447 Ma. Scandian deformation was active by c. 431 Ma and led to overthrusting of the SNC onto subjacent nappes by latest c. 414 Ma. Both the timescale for subduction and the rates of exhumation for the Vaimok Lens reflect subduction-exhumation dynamics of large UHP terranes. Furthermore, the timing of imbrication and Scandian deformation in southern Norrbotten is similar to estimates along strike of the SNC. These results indicate that the SNC acted as a large UHP terrane that underwent a ~25 Myr cycle of subduction and exhumation during the late Cambrian/Early Ordovician, before being deformed and partially dismembered in subsequent accretionary and collisional events.</p><p> </p><p>Research funded by National Science Centre (Poland) project no. 2014/14/E/ST10/00321 to J. Majka.</p>

Quartz deformation in the Marquette and Republic troughs, Upper Peninsula of Michigan

1984 ◽  
Vol 21 (7) ◽  
pp. 793-801 ◽  
Author(s):  
Janet Kappmeyer ◽  
David V. Wiltschko
Keyword(s):  
Subgrain Size ◽  
Stress Regime ◽  
Upper Peninsula ◽  
Metamorphic History ◽  
Dislocation Densities ◽  
History Of ◽  
Peak Metamorphism ◽  
Quartz Fabrics ◽  
Upper Peninsula Of Michigan ◽  
Northern Michigan

Quartz fabrics and microstructures in quartzites of the Mesnard and Goodrich formations were examined to better define the deformation and metamorphic history of the Marquette Synclinorium, northern Michigan. Fabric development is very weak in the whole-rock samples and indicates that mica contamination, extensive annealing, and (or) low imposed strains prevented the formation of distinct c-axis fabrics. However, well defined fabrics are preserved in five quartzite pebbles from the Goodrich conglomerate. Double maxima of varying intensities among these pebbles suggest that the northwest section of the district experienced inhomogeneous shear strain. Measured grain sizes yielded differential stresses ranging from 44 to 548 bar (4.4 to 54.8 MPa). Subgrain size data indicate stresses ranging from 151 to 248 bar (15.1 to 24.8 MPa). Dislocation densities determined by observed etch-pit densities using scanning electron microscopy indicate a range of stresses from 330 to 730 bar (33 to 73 MPa). Stress values from dislocation density measurements vary inversely with metamorphic intensity. Cumulatively, these microstructural data indicate that a low-stress regime of deformation preceded a cooler, higher stress pulse. The data also imply that deformation of the Marquette Synclinorium continued after peak metamorphism, contrary to early hypotheses.

First in-situ Rb-Sr dating of metasedimentary rocks from the Pontiac subprovince, Superior Craton, Canada. Implications towards the regional metamorphic evolution of the sequence.

2020 ◽  
Author(s):  
Nicholas Leventis ◽  
Thomas Zack ◽  
Iain Pitcairn ◽  
Johan Högmalm
Keyword(s):  
Accretionary Prism ◽  
Metasedimentary Rocks ◽  
Metamorphic History ◽  
Accuracy And Precision ◽  
Icp Ms ◽  
Age Variations ◽  
History Of ◽  
Peak Metamorphism ◽  
Superior Craton

<p>The Pontiac subprovince consists of metaturbidites, plutons and thin ultramafic rock layers of Archean age and lies south of the Cadillac-Larder Lake (C-LL) fault zone which is the boundary between the Pontiac and the extensively mineralized Abitibi Greenstone Belt. The sediments show a Barrovian metamorphic gradient which increases southwards, away from the C-LL fault. The most likely tectonic provenance for the Pontiac sedimentary rocks is that they represent a relic accretionary prism with material derived from both the Abitibi and an older terrane. Zircon U-Pb dating shows that deposition occurred not later than 2685±3 Ma ago and recent, robust Lu-Hf dating of garnets bracketed Pontiac's peak metamorphic conditions at 2658±4 Ma. For this study we used a recently developed LA-ICP-MS/MS method for in-situ Rb-Sr dating of biotite and plagioclase in samples ranging in metamorphic grade (biotite to sillimanite zones) from the Pontiac subprovince. Calibration of the instrument was achieved by repeated ablations on several reference materials (see Hogmalm et al. 2017) which also provided the monitoring of accuracy and precision throughout the analyses. Results show a range in dates between 2550 Ma and 2200 Ma with an average of 2440±50 Ma (2σ). Samples from the staurolite and kyanite zones have a larger range with respect to the other zones, but no significant differences are observed in the data with any method of data handing. These dates are ≈300Ma younger than the peak metamorphism in the area and this is attributed to either overgrowth and re-setting of the Rb-Sr system by a second metamorphic/hydrothermal event, or diffusional resetting with core-rim age variations. Possible influence from the adjacent late syntectonic to post-tectonic monzodiorite-monzonite-granodiorite-syenite (MMGS) plutons dated 2671±4 Ma and the garnet-muscovite-granite series (GMG) dated ≈2650 Ma cannot be ruled out. This study provides insights about the metamorphic history of the sequence and supports previous findings regarding resetting of some isotopic systems with relatively low closure temperatures (≈350-400°C) by later thermal events.</p>

Indirect dating of tectonic events by Rb—Sr analysis of syntectonic garnets: an example from schists of the Seve Nappe, central Scandinavian Caledomdes

1982 ◽  
Vol 119 (6) ◽  
pp. 599-604 ◽  
Author(s):  
A. P. S. Reymer
Keyword(s):  
Single Crystal ◽  
The Other ◽  
Metamorphic History ◽  
Tectonic Events ◽  
Scandinavian Caledonides ◽  
Different Ages ◽  
History Of

SummaryRb-Sr analyses of syntectonic single-crystal garnets from the Svartsobacken and Dikanas schist units of the Seve Nappe, Scandinavian Caledonides, show systematic differences. One group yields a Precambrian age spectrum consistent with that given by whole-rock analyses; the other group gives Caledonian ages similar to those given by mica analyses. It follows that the tectonic events reflected in the garnet inclusion patterns are also of different ages and, subject to certain limitations, the method can be used to provide a clearer interpretation of the deformational and metamorphic history of the rock.

scholarly journals Approaches to the Low Grade Metamorphic History of the Karakaya Complex by Chlorite Mineralogy and Geochemistry

Minerals ◽  
2015 ◽  
Vol 5 (2) ◽  
pp. 221-246 ◽  
Author(s):  
Sema Tetiker ◽  
Hüseyin Yalçın ◽  
Ömer Bozkaya
Keyword(s):  
Low Grade ◽  
Metamorphic History ◽  
History Of

Polymetamorphism in the Archean Hemlo – Heron Bay greenstone belt, Superior Province: P–T variations and implications for tectonic evolution

1993 ◽  
Vol 30 (5) ◽  
pp. 985-996 ◽  
Author(s):  
Yuanming Pan ◽  
Michael E. Fleet
Keyword(s):  
Greenstone Belt ◽  
Regional Metamorphism ◽  
Mineral Chemistry ◽  
Superior Province ◽  
Low Grade ◽  
Garnet Porphyroblasts ◽  
Metamorphic History ◽  
Tectonic Environment ◽  
History Of ◽  
Archean Greenstone Belt

The tectono-metamorphic history of the late Archean (2800–2600 Ma) Hemlo – Heron Bay greenstone belt in the Superior Province has been delineated from textural relationships, mineral chemistry, and P–T paths in metapelites, cordierite–orthoamphibole rocks, and metabasites from the White River exploration property, Hemlo area, Ontario. An early low-temperature, medium-pressure metamorphism (about 500 °C and 6–6.5 kbar (1 kbar = 100 MPa)) is indicated by the occurrence of relict kyanite and staurolite porphyroblasts and zoned garnet porphyroblasts in metapelites and the presence of zoned calcic amphiboles in metabasites. This early metamorphism appears to have been coeval with the previously documented D1 deformation that is associated with, for example, low-angle thrusts. A second regional metamorphism predominates in the Hemlo – Heron Bay greenstone belt and is generally of relatively low grade, at about 510–530 °C and 3.2–3.5 kbar, over most of the study area and increases to medium grade (550–650 °C and 4–5 kbar) towards the southern margin with the Pukaskwa Gneissic Complex and along the central axis enclosing the Hemlo Shear Zone. The second regional metamorphism was contemporaneous with the D3 deformation and was probably related to plutonism. This type of polymetamorphism in the Hemlo – Heron Bay greenstone belt may be equivalent to those in Phanerozoic subduction complexes and therefore supports the arc–arc accretion model for the development of the southern Superior Province. Although the Hemlo – Heron Bay greenstone belt most likely represents a single tectonic environment (an oceanic island arc), the restricted occurrence of the relict kyanite and staurolite indicates that the central portion of this Archean greenstone belt probably was at a deeper crustal level at the time of the first metamorphic event.

The Revsegg and Kvitenut Allochthons, Scandinavian Caledonides: origins and evolutions in the Caledonian Wilson cycle

2021 ◽  
pp. jgs2021-062
Author(s):  
Kenneth Warvik ◽  
Håkon Blaker Ringstad ◽  
Lars E. Augland ◽  
Fernando Corfu ◽  
Roy H. Gabrielsen
Keyword(s):  
Final Stage ◽  
Active Margin ◽  
Content Type ◽  
Metasedimentary Rocks ◽  
Scandinavian Caledonides ◽  
Nappe Complex ◽  
Peak Metamorphism ◽  
Wilson Cycle ◽  
Intrusive Suite ◽  
Extensional Setting

The Caledonian Orogen preserves the record of a complete Wilson cycle from rifting to continent-continent collision and orogenic collapse. The Revsegg Allochthon, the uppermost tectonostratigraphic unit of the Hardangervidda-Ryfylke Nappe Complex of the southern Scandinavian Caledonides, is an understudied example illustrating key temporal and tectonic stages in a Wilson cycle. It overlies 1600-1500 Ma gneisses of the Kvitenut Allochthon that were deformed, metamorphosed and juxtaposed onto the Dyrskard Allochthon at 1000 Ma. The Revsegg Allochthon consists of leucosome-bearing mica-schists with meta-sandstone, and amphibolite and granitoids lenses. The timing of sedimentation of metasedimentary rocks is constrained to the period 780 - 495 Ma, but its association with a 495 Ma bimodal mafic and felsic intrusive suite suggests concurrent sedimentation in a Cambrian extensional setting. The Revsegg Allochthon underwent peak metamorphism at 480-470 Ma, followed by several metamorphic stages from 460 to 440 Ma, probably at an active margin outboard of Baltica, as postulated for the eclogite-bearing Jæren Nappe to the southeast. The Revsegg Allochthon was thrust onto the Kvitenut-Dyrskard duplex from 437 Ma to 434 Ma during an early Scandian phase also recognized in the Seve Nappe. Syn-deformational pegmatites, emplaced at 428 Ma represent the final stage in the nappe stack development. Thematic collection: This article is part of the Caledonian Wilson cycle collection available at: https://www.lyellcollection.org/cc/caledonian-wilson-cycle

Monazite behaviour during metamorphic evolution of a diamond-bearing gneiss: a case study from the Seve Nappe Complex, Scandinavian Caledonides

2019 ◽  
Author(s):  
I Petrík ◽  
M Janák ◽  
I Klonowska ◽  
J Majka ◽  
N Froitzheim ◽  
...  
Keyword(s):  
Granulite Facies ◽  
Age Dating ◽  
Prograde Metamorphism ◽  
Metamorphic Evolution ◽  
Heavy Rare Earth Element ◽  
Rock Composition ◽  
Scandinavian Caledonides ◽  
Nappe Complex ◽  
The Matrix ◽  
Seve Nappe Complex

Abstract Monazite is a common mineral in metapelitic rocks including those which underwent ultra-high pressure (UHP) metamorphism. During metamorphic evolution monazite adapts its composition to the changing mineral assemblage, especially in its heavy rare earth element contents. We studied this process in diamond-bearing gneiss containing monazite, from Saxnäs in the Seve Nappe Complex of the Scandinavian Caledonides. Although the rock has been re-equilibrated under granulite facies and partial melting conditions, it still preserves minerals from the UHP stage: garnet, kyanite, rutile, and especially diamond. Microdiamonds occur in situ as inclusions in garnet, kyanite and zircon, either as single-crystals or polyphase inclusions with Fe-Mg carbonates, rutile and CO2. Both monazite and diamond occur in the rims of garnet showing the highest pyrope content and a secondary peak of yttrium. Such a position indicates thermally activated diffusion under high temperature at the end of prograde metamorphism. Monazite compositions show negative Eu anomalies, which we interpret to be inherited from the source rock, not reflecting the coexistence with plagioclase and/or K-feldspar which are unstable at UHP conditions. Our results suggest that the effect of whole-rock composition may be more important than that of coexisting phases. The UHP monazite was most likely formed from allanite during subduction and prograde metamorphism. The monazites included in garnet and kyanite are mostly unaltered, whereas those in the matrix show breakdown coronas consisting of apatite, REE-epidote/allanite and REE carbonate, likely formed due to pressure decrease and cooling. U-Th-Pb chemical age dating of monazites yields an isochron centroid age of 472 ±3 Ma. We interpret this age as monazite growth under UHP conditions related to subduction of the Baltica continental margin in Early Ordovician time.

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