Metamorphic Facies and Deformation Fabrics Diagnostic of Subduction: Insights From 2D Numerical Models

Regorda, Alessandro; Spalla, Maria Iole; Roda, Manuel; Lardeaux, Jean‐Marc; Marotta, Anna

doi:10.1029/2021gc009899

Cited by 11 publications

(19 citation statements)

References 129 publications

(266 reference statements)

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“…In the Southalpine domain, andalusite mostly occurs in high-temperature basement rocks that include sillimanite, cordierite, and/or spinel that reflect Permian-Triassic Buchan/Abukuma-type metamorphism. In the upper Val Camonica, andalusite is instead found in chloritoid-staurolite-garnet-bearing metapelites, which suggest higher P/T conditions as characteristic of Barrovian/Dalradian metamorphism [1,2]. This case study thus represents an excellent opportunity to improve our understanding of the Variscan basement exhumation path, from the Variscan convergence to the Permian-Triassic lithospheric thinning.…”

Section: Introductionmentioning

confidence: 88%

“…Andalusite is an indicator of high thermal regimes, such as those characterizing contact metamorphism or regional Buchan/Abukuma-type metamorphism in the metapelites of the continental crust [1,2]. High T/P ratios accountable for andalusite development are envisaged in various convergent and divergent settings, including late-orogenic thinning and lithospheric delamination in the mature stages of continental collision, as well as lithospheric thinning announcing continental rifting in post-orogenic settings [3,4].…”

Section: Introductionmentioning

confidence: 99%

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Cld-St-And-Bearing Assemblages in the Central Southalpine Basement: Markers of an Evolving Thermal Regime during Variscan Convergence

et al. 2021

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Multiscale structural analysis was carried out to explore the sequence of superposed pre-Alpine chloritoid–staurolite–andalusite metamorphic assemblages in the polydeformed Variscan basement of the upper Val Camonica, in the central Southalpine domain. The dominant fabric in the upper Val Camonica basement is the late-Variscan S2 foliation, marked by greenschist facies minerals and truncated by the base of Permian siliciclastic sequences. The intersection with the sedimentary strata defines a Permianage limit on the pre-Alpine tectonometamorphic evolution and exhumation of the Variscan basement. The detailed structural survey revealed that the older S1 foliation was locally preserved in low-strained domains. S1 is a composite fabric resulting from combining S1a and S1b: in the metapelites, S1a was supported by chloritoid, garnet, and biotite and developed before S1b, which was marked by staurolite, garnet, and biotite. S1a and S1b developed at intermediate pressure amphibolite facies conditions during the Variscan convergence, S1a at T = 520–550 °C and P ≃ 0.8 GPa, S1b at T = 550–650 °C and P = 0.4–0.7 GPa. The special feature of the upper Val Camonica metapelites is andalusite, which formed between the late D1b and early D2 tectonic events. Andalusite developed at T = 520–580 °C and P = 0.2–0.4 GPa in pre-Permian times, after the peak of the Variscan collision and before the exhumation of the Variscan basement and the subsequent deposition of the Permian covers. It follows that the upper Val Camonica andalusite has a different age and tectonic significance as compared to that of other pre-Alpine andalusite occurrences in the Alps, where andalusite mostly developed during exhumation of high-temperature basement rocks in Permian–Triassic times.

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Section: Introductionmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Cld-St-And-Bearing Assemblages in the Central Southalpine Basement: Markers of an Evolving Thermal Regime during Variscan Convergence

et al. 2021

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“…Metagranitoids (Apgr1) and metagabbros (Apg1) emplacement conditions are also reported (Table 1). Metamorphic facies modified after [111][112][113][114]. Black arrows represent geothermal gradients traditionally associated to arc regions (A) and plate interior (Pi), warm subduction complexes (WS), and cold subduction complexes (CS), as presented by [115].…”

Section: Thermobarometrymentioning

confidence: 99%

Quantitative X-ray Maps Analaysis of Composition and Microstructure of Permian High-Temperature Relicts in Acidic Rocks from the Sesia-Lanzo Zone Eclogitic Continental Crust, Western Alps

et al. 2021

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Three samples of meta-acidic rocks with pre-Alpine metamorphic relicts from the Sesia-Lanzo Zone eclogitic continental crust were investigated using stepwise controlled elemental maps by means of the Quantitative X-ray Maps Analyzer (Q-XRMA). Samples were chosen with the aim of analysing the reacting zones along the boundaries between the pre-Alpine and Alpine mineral phases, which developed in low chemically reactive systems. The quantitative data treatment of the X-ray images was based on a former multivariate statistical analytical stage followed by a sequential phase and sub-phase classification and permitted to isolate and to quantitatively investigate the local paragenetic equilibria. The parageneses thus observed were interpreted as related to the pre-Alpine metamorphic or magmatic stages as well as to local Alpine re-equilibrations. On the basis of electron microprobe analysis, specific compositional ranges were defined in micro-domains of the relict and new paragenetic equilibria. In this way calibrated compositional maps were obtained and used to contour different types of reacting boundaries between adjacent solid solution phases. The pre-Alpine and Alpine mineral parageneses thus obtained allowed to perform geothermobarometry on a statistically meaningful and reliable dataset. In general, metamorphic temperatures cluster at 600–700 ∘C and 450–550 ∘C, with lower temperatures referred to a retrograde metamorphic re-equilibration. In all the cases described, pre-Alpine parageneses were overprinted by an Alpine metamorphic mineral assemblage. Pressure-temperature estimates of the Alpine stage averagely range between 420 to 550 ∘C and 12 to 16.5 kbar. The PT constraints permitted to better define the pre-Alpine metamorphic scenario of the western Austroalpine sectors, as well as to better understand the influence of the pre-Alpine metamorphic inheritance on the forthcoming Alpine tectonic evolution.

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“…Such numerical models have been applied to investigate the mechanisms of exhumation of (U)HP rocks within Alpine‐type collisional belts (e.g., Burov et al., 2001; Butler et al., 2014; Gerya et al., 2002; Ruh et al., 2015; Stöckhert & Gerya, 2005; Warren et al., 2008; Yamato et al., 2008, 2007). Several of these studies trace individual numerical markers (e.g., Gerya & Yuen, 2003) in order to assess P ‐ T ‐ t trajectories during syn‐convergent exhumation (e.g., Butler et al., 2014; Gerya et al., 2002; Regorda et al., 2021; Ruh et al., 2015; Stöckhert & Gerya, 2005; Warren et al., 2008; Yamato et al., 2008, 2007). Although such numerical models successfully reproduce individual exhumation P ‐ T ‐ t trajectories that are comparable to the Alps (e.g., Butler et al., 2014; Gerya & Yuen, 2003; Ruh et al., 2015; Warren et al., 2008; Yamato et al., 2008, 2007), only few numerical modeling studies (e.g., Butler et al., 2014; Regorda et al., 2021) attempted to reproduce the spatially continuous distributions of metamorphic facies and the entire, regional‐scale metamorphic architecture of the Western Alps (Figure 2).…”

Section: Introductionmentioning

confidence: 99%

“…Such numerical models have been applied to investigate the mechanisms of exhumation of (U)HP rocks within Alpine-type collisional belts (e.g., Burov et al, 2001;Butler et al, 2014;Gerya et al, 2002;Ruh et al, 2015;Stöckhert & Gerya, 2005;Warren et al, 2008;Yamato et al, 2008Yamato et al, , 2007. Several of these studies trace individual numerical markers (e.g., Gerya & Yuen, 2003) in order to assess P-T-t trajectories during syn-convergent exhumation (e.g., Butler et al, 2014;Gerya et al, 2002;Regorda et al, 2021;Ruh et al, 2015;Stöckhert & Gerya, 2005;Warren et al, 2008;Yamato et al, 2008Yamato et al, , 2007. Although such numerical models successfully reproduce individual exhumation P-T-t trajectories that are comparable to the Alps (e.g., Butler et al, 2014;Gerya & Yuen, 2003;Ruh et al, 2015;Warren et al, 2008;Yamato et al, 2008Yamato et al, , 2007, (b) Approximate pressure-temperature metamorphic facies grid (modified after Philpotts & Ague, 2009) with representative P-T estimates for Western Alpine units (dashed and solid lines are used for clearer visualization), BIU = (Rubatto & Hermann, 2001), MR = (Luisier et al, 2019;Vaughan-Hammon et al, 2021b), SE = (Lardeaux et al, 1982;Vuichard & Ballevre, 1988), VA = (Bousquet et al, 2002;Goffé & Bousquet, 1997;Wiederkehr et al, 2007), GP = (Bousquet et al, 2008;Manzotti et al, 2018), LU = (Wiederkehr et al, 2008), DB = (Cortiana et al, 1998...…”

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confidence: 99%

Metamorphic Facies Distribution in the Western Alps Predicted by Petrological‐Thermomechanical Models of Syn‐Convergent Exhumation

Vaughan‐Hammon

Candioti

Duretz

et al. 2022

Geochem Geophys Geosyst

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The distribution of metamorphic rocks throughout the western European Alps indicates subduction‐related metamorphism. However, processes by which high‐grade metamorphic rocks exhume remain disputed. Here, we present two‐dimensional petrological‐thermomechanical numerical models to investigate the metamorphic facies evolution during orogenesis. We model closure of an oceanic basin with exhumed mantle bounded by passive margins. To ensure thermomechanical feasibility, we model also this basin configuration. Before convergence, we replace the uppermost portions of exhumed mantle with serpentinite. Location and orientation of subduction are not predefined and subduction initiates self‐consistently during convergence. A weak subduction interface develops if serpentinite is initially thick enough (here 6 km) and can distribute along the interface. Syn‐convergent exhumation of (ultra)high‐pressure rocks occurs with minor erosion, enabled by local upper‐plate extension and a crustal‐scale normal‐sense shear zone. We calculate metamorphic facies evolutions with peak P and T values of 10,000 markers. Results show (a) peak P and T values agreeing with estimates from natural rocks, (b) exhumed, structurally coherent regions with identical metamorphic facies, indicating absence of significant mixing (mélange), (c) facies distributions corresponding to that of the Western Alps, which is from eclogite to blueschist to greenschist facies when going from internal to external domains, and (d) exhumation velocities larger than burial velocities. Models with stronger subduction interface (3‐km serpentinite thickness) develop an orogenic wedge with vertical metamorphic gradient and minor exhumation. Syn‐convergent exhumation is feasible for the Western Alps and calculating metamorphic facies distribution is useful when testing the applicability of models to natural orogens.

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Metamorphic Facies and Deformation Fabrics Diagnostic of Subduction: Insights From 2D Numerical Models

Cited by 11 publications

References 129 publications

Cld-St-And-Bearing Assemblages in the Central Southalpine Basement: Markers of an Evolving Thermal Regime during Variscan Convergence

Cld-St-And-Bearing Assemblages in the Central Southalpine Basement: Markers of an Evolving Thermal Regime during Variscan Convergence

Quantitative X-ray Maps Analaysis of Composition and Microstructure of Permian High-Temperature Relicts in Acidic Rocks from the Sesia-Lanzo Zone Eclogitic Continental Crust, Western Alps

Metamorphic Facies Distribution in the Western Alps Predicted by Petrological‐Thermomechanical Models of Syn‐Convergent Exhumation

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