Structural and metamorphic inheritance controls strain partitioning during orogenic shortening (Kalak Nappe Complex, Norwegian Caledonides)

Ceccato, Alberto; Menegon, Luca; Warren, Clare J.; Halton, Alison M.

doi:10.1016/j.jsg.2020.104057

Cited by 8 publications

(4 citation statements)

References 69 publications

(141 reference statements)

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“…From top to bottom, these are the KNC and Laksefjord Nappe Complex (LNC; both Middle Allochthon), several units of the Window Allochthon (Komagfjord Antiformal Stack [KAS], Kunes Nappe, and the unexposed Hatteras and Revsbotn Basement Horses; Gayer et al (1987)), and the Gaissa Nappe Complex (GNC; Lower Allochthon). Metamorphic grade decreases down the nappe pile, with Barrovian‐type sillimanite‐zone metapelites in the upper nappes of the KNC to rocks of the Barrovian‐type garnet to biotite zones in the lower nappes (e.g., Ceccato et al, 2020; Rice, 1984, 1985). Whereas epizone grade has been reported for the LNC and the cover sediments around the KAS, the GNC reached upper anchizone grade (Rice et al, 1989).…”

Section: Regional Geologymentioning

confidence: 99%

Testing the equilibrium model: An example from the Caledonian Kalak Nappe Complex (Finnmark, Arctic Norway)

Gaidies

Heldwein

Yogi

et al. 2021

Journal Metamorphic Geology

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The equilibrium model has been tested using Barrovian garnet-zone micaschists of the Kalak Nappe Complex. In our model, equilibrium in the MnNCKFMASHT system was established across the entire rock volume during prograde metamorphism except for garnet, which developed growth zoning preserved at levels controlled by the kinetics of intracrystalline diffusion. The preservation potential of the disequilibrium fluctuations required for nucleation of garnet has been considered in our simulations, using a moving boundary multicomponent diffusion and growth model. Results indicate that the core of garnet that crystallizes during regional metamorphism does not retain the major element composition of the nucleus but reflects the compositional signature of the immediate overgrowth. The differences between the metamorphic conditions of successive garnet growth steps of the samples indicate characteristic trends in their pressure-temperature evolutions that can be predicted with the equilibrium model. There is some latitude with regard to the absolute metamorphic conditions due to the inherent uncertainty of the thermodynamic data and the approximation of the reactive volume composition. However, the slopes of the pressure-temperature paths together with systematic trends in the lithological, geochemical, and Lu-Hf garnet whole-rock isotopic properties of the rocks, as well as their garnet crystal size frequency distributions, enable the identification of the Veidnes, Bekkarfjord, and Kolvik Nappes involved in the Caledonian Orogeny and provide new insight into their metamorphic evolutions. According to our findings, the base of the Kalak Nappe Complex experienced wide-spread Barrovian-type metamorphism at c. 420 Ma with a gradient of $40 bar/ C and peak conditions of $560 C and 6.7 kbar in the Bekkarfjord and Veidnes Nappes, whereas the hinterland-placed Kolvik Nappe was metamorphosed at peak conditions of $590 C and 7.5 kbar. This event was preceded by moderate-pressure metamorphism at c. 423 Ma resulting in garnet crystallization exclusively in the Bekkarfjord Nappe, along a gradient of $20 bar/ C and peak conditions of $570 C and 6.0 kbar. We consider both of these metamorphic and deformational episodes to be different

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Section: Regional Geologymentioning

confidence: 99%

Testing the equilibrium model: An example from the Caledonian Kalak Nappe Complex (Finnmark, Arctic Norway)

Gaidies

Heldwein

Yogi

et al. 2021

Journal Metamorphic Geology

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“…The KNC crops out as nappe stacks with SE–ESE vergence, positioned structurally above the Laksefjord nappe (Rice, 2001; Roberts & Gromet, 2009) and the Gaissa (Gayer et al, 1987) nappe complex (Figure 1). These nappes are separated from each other by thrusts that accommodated SE‐directed tectonic transport during the collision between Baltica and Laurentia (e.g., Ceccato et al, 2020; Gayer et al, 1987; Giuntoli et al, 2020; Roberts, 2003).…”

Section: Regional Geologymentioning

confidence: 99%

Mechanisms and durations of metamorphic garnet crystallization in the lower nappes of the Caledonian Kalak Nappe Complex, Arctic Norway

Yogi,

Gaidies,

Heldwein

et al. 2024

Journal Metamorphic Geology

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The 3D microstructure and compositional zoning of garnet populations in micaschists from the Kolvik and Bekkarfjord nappes indicate the quasi‐equilibration of their major components across the rock matrices during interface‐controlled, size‐independent garnet growth. There is microstructural evidence for foliation‐parallel, small‐scale resorption of garnet rims in the Kolvik Nappe, influencing the metamorphic peak conditions obtained from thermodynamic modelling. The local chemical compositions of rims less affected by resorption indicate a peak temperature of ~630°C, which is ~40°C higher than the temperature obtained from resorbed rims of the largest garnet crystal. Using a diffusion geospeedometry approach that considers the geometry of the compositional zoning of the garnet population, as well as the higher, more realistic peak temperature, a duration of 1 to 4.9 Myr is obtained for garnet growth in the Kolvik Nappe. This is approximately 1 order of magnitude faster than duration estimates obtained when using the apparent, lower temperature estimated from the resorbed garnet rims. Concomitantly to garnet growth in the Kolvik Nappe, garnet overgrowths formed in the Bekkarfjord Nappe for circa 2.5 Myr at metamorphic peak temperatures of ~560°C. The garnet growth durations obtained here are comparable with the uncertainty on the Lu–Hf garnet–whole rock isochron ages of 419.9 ± 2.4 Ma and 423.0 ± 1.9 Ma, previously obtained for these rocks. These results provide new insight into the timescales of repeated Barrovian‐type metamorphic events experienced by the lower nappes of the Kalak Nappe Complex during the Caledonian Orogeny in Arctic Norway. This study emphasizes the importance of microstructural and chemical characterization of garnet populations in assessing metamorphic crystallization mechanisms and the extent of equilibration of garnet‐forming components during prograde metamorphism. Moreover, our results provide means for reducing the uncertainty on metamorphic durations obtained via diffusion geospeedometry and, so, contributing to our understanding of geological timescales and processes.

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“…For example, depending on the composition and the fluid content, lithospheric plates may present different mechanical behavior (brittle vs. viscous deformation) and strength at the same depth and temperature conditions during collision (Behr & Platt, 2014; Bürgmann & Dresen, 2008; Jamtveit et al., 2019; Menegon et al., 2011). Furthermore, the occurrence of anisotropic structural fabrics (foliations and fractures), strictly related to the geological history of crustal sections, may promote or hinder deformation depending on their suitability to be reactivated, and/or their ability to promote or hinder fluid infiltration (Ceccato, Menegon, et al., 2020; Zertani et al., 2023). Pressure, temperature, fluid, and structural fabrics evolve with the tectono‐metamorphic evolution of a collisional orogen, and so do their effects on the rheological contrast between colliding plates (Behr & Platt, 2013; Bellanger et al., 2014; Ceccato, Menegon, et al., 2020; Groome et al., 2008).…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, the occurrence of anisotropic structural fabrics (foliations and fractures), strictly related to the geological history of crustal sections, may promote or hinder deformation depending on their suitability to be reactivated, and/or their ability to promote or hinder fluid infiltration (Ceccato, Menegon, et al., 2020; Zertani et al., 2023). Pressure, temperature, fluid, and structural fabrics evolve with the tectono‐metamorphic evolution of a collisional orogen, and so do their effects on the rheological contrast between colliding plates (Behr & Platt, 2013; Bellanger et al., 2014; Ceccato, Menegon, et al., 2020; Groome et al., 2008).…”

Section: Introductionmentioning

confidence: 99%

Structural Evolution, Exhumation Rates, and Rheology of the European Crust During Alpine Collision: Constraints From the Rotondo Granite—Gotthard Nappe

Ceccato,

Behr,

Zappone

et al. 2024

Tectonics

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The rheology of crystalline units controls the large‐scale deformation geometry and dynamics of collisional orogens. Defining a time‐constrained rheological evolution of such units may help unravel the details of collisional dynamics. Here, we integrate field analysis, pseudosection calculations and in situ garnet U–Pb and mica Rb–Sr geochronology to define the structural and rheological evolution of the Rotondo granite (Gotthard nappe, Central Alps). We identify a sequence of four (D1–D4) deformation stages. Pre‐collisional D1 brittle faults developed before Alpine peak metamorphism, which occurred at 34–20 Ma (U–Pb garnet ages) at 590 ± 25°C and 0.9 ± 0.1 GPa. The reactivation of D1 structures controlled the rheological evolution, from D2 reverse mylonitic shearing at amphibolite facies (520 ± 40°C and 0.8 ± 0.1 GPa) at 18–20 Ma (white mica Rb–Sr ages), to strike‐slip, brittle‐ductile shearing at greenschist‐facies D3 (395 ± 25°C and 0.4 ± 0.1 GPa) at 14–15 Ma (white mica and biotite Rb–Sr ages), and then to D4 strike‐slip faulting at shallow conditions. Although highly misoriented for the Alpine collisional stress orientation, D1 brittle structures controlled the localization of D2 ductile mylonites accommodating fast (∼3 mm/yr) exhumation rates due to their weak shear strength (<10 MPa). This structural and rheological evolution is common across External Crystalline Massifs (e.g., Aar, Mont Blanc), suggesting that the European upper crust was extremely weak during Alpine collision, its strength controlled by weak ductile shear zones localized on pre‐collisional deformation structures, that in turn controlled localized exhumation at the scale of the orogen.

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Structural and metamorphic inheritance controls strain partitioning during orogenic shortening (Kalak Nappe Complex, Norwegian Caledonides)

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Cited by 8 publications

References 69 publications

Testing the equilibrium model: An example from the Caledonian Kalak Nappe Complex (Finnmark, Arctic Norway)

Testing the equilibrium model: An example from the Caledonian Kalak Nappe Complex (Finnmark, Arctic Norway)

Mechanisms and durations of metamorphic garnet crystallization in the lower nappes of the Caledonian Kalak Nappe Complex, Arctic Norway

Structural Evolution, Exhumation Rates, and Rheology of the European Crust During Alpine Collision: Constraints From the Rotondo Granite—Gotthard Nappe

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