scholarly journals Diachronous collision in the Seve Nappe Complex: Evidence from Lu‐Hf geochronology of eclogites (Norrbotten, North Sweden)

2021 ◽  
Author(s):  
Kathrin Fassmer ◽  
Nikolaus Froitzheim ◽  
Marian Janák ◽  
Merle Strohmeyer ◽  
Michał Bukała ◽  
...  
Keyword(s):  
Nappe Complex ◽  
Seve Nappe Complex ◽  
North Sweden

NEW AGES CONSTRAIN TIMING OF CALEDONIAN METAMORPHISM ACROSS VÄSTERBOTTEN, SEVE NAPPE COMPLEX, SWEDEN

2020 ◽  
Author(s):  
Emily O. Walsh ◽  
◽  
Michael W. McRivette ◽  
Morgan Casarez ◽  
Jillian Shew ◽  
...  
Keyword(s):  
Nappe Complex ◽  
Seve Nappe Complex

Regional study of orogenic ultramafics of the Seve Nappe Complex, Scandinavian Caledonides - preliminary results from northern and central Jämtland, Sweden

2021 ◽  
Author(s):  
Daniel Buczko ◽  
Magdalena Matusiak-Małek ◽  
Jarosław Majka ◽  
Iwona Klonowska ◽  
Grzegorz Ziemniak
Keyword(s):  
Preliminary Data ◽  
Regional Study ◽  
Scandinavian Caledonides ◽  
Nappe Complex ◽  
Science Centre ◽  
Seve Nappe Complex ◽  
End Members ◽  
Very High ◽  
Different Levels ◽  
High Range

<p>The Scandinavian Caledonides comprise numerous ultramafic bodies emplaced within metamorphic nappe complexes. A hypothetical suture between the most distal crustal units representing Baltican margin (Seve Nappe Complex, SNC) with the oceanic Iapetian terranes (Köli Nappe Complex) is abundant in such occurrences. Here we present preliminary data on garnet/spinel peridotites/pyroxenites from SNC in central and northern parts of Swedish Jämtland county. The presented results are a part of a project involving regional study focused on orogenic peridotites (mostly spinel-bearing) of Seve and Köli nappe complexes. </p><p>The ultramafic bodies in the study area range from a meters to kilometer scale and comprise: 1) garnet peridotites, 2) spinel peridotites, 3) spinel pyroxenites and 4) garnet pyroxenites. Individual outcrops often record different levels of serpentinisation. </p><p>The Grt-peridotites are usually harzburgites (sparsely dunites/lherzolites) with an assemblage of Ol+Opx+Cpx+Amph+Grt+Spl.  Minerals within the Grt-peridotites are characterised by Ol Fo=~90-91 and Mg# in pyroxenes 90-92 and 92-96 (enstatite and diopside/Cr-diopside, respectively). Garnet is pyrope with end-members Prp=60-69%, Usp=0-4% and Cr#=0.5-4. Amphibole (pargasite; Mg#=88-92) typically occurs as patches or rims around Grt and often host significant amounts of Spl. The spinel has an intermediate composition between hercynite-spinel and magnesiochromite-chromite (Cr#=41-55, Mg#=40-57). </p><p>The spinel peridotites are formed of Ol+Opx+Amph+Chl+Spl and classify mostly as harzburgites/dunites. Olivine and Opx (enstatite, rarely Cr-enstatite; often as porphyrocrysts) show a high range of Fo/Mg# values (90-95 and 90-94, respectively). Amphibole (tremolite; Mg#=91-96) is usually evenly distributed within the rock, while Chl is often associated with grain boundaries. Spinel has a chromite composition (Cr#=82-100, Mg#=5-10). Within single large (~0.5mm) spinel grains, cores with higher Mg# (~23) and lower Cr# (~82) can be observed.</p><p>The garnet pyroxenites are websterites characterised by lower Mg# (88-90) in enstatite, presence of Al-diopside and lower Cr# (<0.5) in pyrope than in peridotites. The Spl-pyroxenites are orthopyroxenites with Mg# in enstatite (86-88) lower than in peridotitic orthopyroxene.</p><p>The presented preliminary data suggest that lithologies formed under different pressures (i.e. Grt and Spl facies) and must have recorded different evolution paths. Garnet ultramafics mineralogy resembles typical “mantle” assemblage with Prg suggesting possible metamorphic input also for other consisting phases (similarly to M2 paragenesis described in [1]). While the Grt ultramafic rocks and their evolution has been a subject of several studies before, the Spl ultramafics are relatively understudied and can shed new light on the evolution of SNC. The composition of Spl peridotites represents a mixture of typical “magmatic” mantle phases with metamorphic minerals (Amph+Chl). Very high Mg# values and occurrence of 120° triple point junctions in Ol (also described in [2]) suggest complex genesis, which probably includes serpentinisation (+exhumation?) followed by deserpentinisation. This indicates that the Spl ultramafics of SNC might have been subducted after their primary serpentinisation, which can be related either to emplacement and exhumation of ultramafics during Rodinia breakup or derivation from shallow, serpentinised “wet” mantle wedge in the subduction zone. </p><p>Research founded by Polish National Science Centre grant no. 2019/35/N/ST10/00519.</p><p>[1] Gilio et al. (2015). Lithos 230, 1-16.<br>[2] Clos et al. (2014). Lithos 192-195, 8-20.</p>

scholarly journals Anisotropic Kirchhoff pre-stack depth migration at the COSC-1 borehole, central Sweden

2019 ◽  
Vol 219 (1) ◽  
pp. 66-79 ◽  
Author(s):  
H Simon ◽  
S Buske ◽  
P Hedin ◽  
C Juhlin ◽  
F Krauß ◽  
...  
Keyword(s):  
Regional Scale ◽  
Seismic Profile ◽  
Black Shales ◽  
Data Sets ◽  
Data Set ◽  
Depth Migration ◽  
Scandinavian Caledonides ◽  
Long Offset ◽  
Nappe Complex ◽  
Seve Nappe Complex

SUMMARYA remarkably well preserved representation of a deeply eroded Palaeozoic orogen is found in the Scandinavian Caledonides, formed by the collision of the two palaeocontinents Baltica and Laurentia. Today, after 400 Ma of erosion along with uplift and extension during the opening of the North Atlantic Ocean, the geological structures in central western Sweden comprise far transported allochthonous units, the underlying Precambrian crystalline basement, and a shallow west-dipping décollement that separates the two and is associated with a thin layer of Cambrian black shales. These structures, in particular the Seve Nappes (upper part of the Middle Allochthons), the Lower Allochthons and the highly reflective basement are the target of the two approximately 2.5 km deep fully cored scientific boreholes in central Sweden that are part of the project COSC (Collisional Orogeny in the Scandinavian Caledonides). Thus, a continuous 5 km tectonostratigraphic profile through the Caledonian nappes into Baltica’s basement will be recovered. The first borehole, COSC-1, was successfully drilled in 2014 and revealed a thick section of the seismically highly reflective Lower Seve Nappe. The Seve Nappe Complex, mainly consisting of felsic gneisses and mafic amphibolites, appears to be highly anisotropic. To allow for extrapolation of findings from core analysis and downhole logging to the structures around the borehole, several surface and borehole seismic experiments were conducted. Here, we use three long offset surface seismic profiles that are centred on the borehole COSC-1 to image the structures in the vicinity of the borehole and below it. We applied Kirchhoff pre-stack depth migration, taking into account the seismic anisotropy in the Seve Nappe Complex. We calculated Green’s functions using an anisotropic eikonal solver for a VTI (transversely isotropic with vertical axis of symmetry) velocity model, which was previously derived by the analysis of VSP (Vertical Seismic Profile) and surface seismic data. We show, that the anisotropic results are superior to the corresponding isotropic depth migration. The reflections appear significantly more continuous and better focused. The depth imaging of the long offset profiles provides a link between a high-resolution 3-D data set and the regional scale 2-D COSC Seismic Profile and complements these data sets, especially in the deeper parts below the borehole. However, many of the reflective structures can be observed in the different data sets. Most of the dominant reflections imaged originate below the bottom of the borehole and are situated within the Precambrian basement or at the transition zones between Middle and Lower Allochthons and the basement. The origin of the deeper reflections remains enigmatic, possibly representing dolerite intrusions or deformation zones of Caledonian or pre-Caledonian age.

Microdiamond on Åreskutan confirms regional UHP metamorphism in the Seve Nappe Complex of the Scandinavian Caledonides

2017 ◽  
Vol 35 (5) ◽  
pp. 541-564 ◽  
Author(s):  
I. Klonowska ◽  
M. Janák ◽  
J. Majka ◽  
I. Petrík ◽  
N. Froitzheim ◽  
...  
Keyword(s):  
Uhp Metamorphism ◽  
Scandinavian Caledonides ◽  
Nappe Complex ◽  
Seve Nappe Complex

scholarly journals Seismic imaging in the eastern Scandinavian Caledonides: siting the 2.5 km deep COSC-2 borehole, central Sweden

2016 ◽  
Author(s):  
C. Juhlin ◽  
P. Hedin ◽  
D. G. Gee ◽  
H. Lorenz ◽  
T. Kalscheuer ◽  
...  
Keyword(s):  
Surface Structure ◽  
High Pressures ◽  
Hydrological Cycle ◽  
Magnetic Data ◽  
Lower Grade ◽  
Seismic Profiles ◽  
Scientific Drilling ◽  
Scandinavian Caledonides ◽  
Nappe Complex ◽  
Seve Nappe Complex

Abstract. The Collisional Orogeny in the Scandinavian Caledonides (COSC) project, a contribution to the International Continental Scientific Drilling Program (ICDP), aims to provide a deeper understanding of mountain belt dynamics. Scientific investigations include a range of topics, from subduction-related tectonics to the present-day hydrological cycle. COSC investigations and drilling activities are focused in central Scandinavia where rocks from the mid to lower crust of the orogen are exposed near the Swedish-Norwegian border. Here, rock units of particular interest occur in the Seve Nappe Complex (SNC) of the so-called Middle Allochthon and include granulite facies migmatites (locally with evidence of ultra-high pressures) and amphibolite facies gneisses and mafic rocks. This complex overlies greenschist facies metasedimentary rocks of the dolerite-intruded Särv Nappes and underlying, lower grade Jämtlandian Nappes (Lower Allochthon). Reflection seismic profiles have been an important component in the activities to image the sub-surface structure in the area. Sub-horizontal reflections in the upper 1–2 km are underlain and interlayered with strong west- to northwest-dipping reflections, suggesting significant east-vergent thrusting. Two 2.5 km deep fully cored boreholes are a major component of the project which will improve our understanding of the sub-surface structure and tectonic history of the area. Borehole COSC-1, drilled in the summer of 2014, targeted the subduction-related Seve Nappe Complex and the contact with the underlying allochthon. The COSC-2 borehole will be located further east and investigate the lower grade, mainly Cambro-Silurian rocks of the Lower Allochthon, the main Jämtlandian décollement and penetrate into the crystalline basement rocks to identify the source of some of the northwest-dipping reflections. A series of high resolution seismic profiles have been acquired along a composite ca. 55 km long profile to help locate the COSC drillholes. We present here the results from this COSC-related composite seismic profile (CSP), including new interpretations based on previously unpublished data acquired between 2011 and 2014. These seismic data, along with shallow drillholes in the Caledonian thrust front and previously acquired seismic, magnetotelluric, and magnetic data, are used to identify two potential drill sites for the COSC-2 borehole.

scholarly journals Ba- and Ti-enriched dark mica from the UHP metasediments of the Seve Nappe Complex, Swedish Caledonides

Mineralogia ◽  
2015 ◽  
Vol 46 (1-2) ◽  
pp. 41-50
Author(s):  
Jarosław Majka ◽  
Łukasz Kruszewski ◽  
Åke Rosén ◽  
Iwona Klonowska
Keyword(s):  
Granulite Facies ◽  
Stability Field ◽  
Metasedimentary Rocks ◽  
High Pressure Metamorphism ◽  
Nappe Complex ◽  
Crystallochemical Formula ◽  
Seve Nappe Complex ◽  
The Mean ◽  
End Members ◽  
Parental Rock

AbstractWe report on the occurrence of peculiar Ba- and Ti-enriched dark mica in metasedimentary rocks that underwent high-pressure metamorphism in the diamond stability field followed by decompression to granulite facies conditions. The mica occurs as well-developed preserved laths in a quartzofeldspathic matrix. The mean concentrations of BaO and TiO2in the mica are 11.54 and 7.80wt%, respectively. The maximum amounts of these components are 13.38wt% BaO and 8.45wt% TiO2. The mean crystallochemical formula can be expressed as (K0.54Ba0.39Na0.02Ca0.01)Σ0.96(Fe1.37Mg0.85Ti0.50Al0.29Mn0.01Cr0.01)Σ3.03(Si2.59Al1.41)Σ4.00O10(OH1.30O0.66F0.02S0.01)Σ1.99, withoxyannite,oxy-ferrokinoshitaliteand siderophyllite as dominating end-members. Based on the petrographical observations, it is proposed that the dark mica was formed at a rather late stage in the evolution of the parental rock, i.e. under granulite facies conditions.

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