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Structural and Metamorphic Evolutions of the Pre-Alpine Lithosphere of the Alps

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A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Deposits".

Deadline for manuscript submissions: closed (22 October 2021) | Viewed by 9383

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Special Issue Editors

Dr. Manuel Roda

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Guest Editor

Università degli Studi di Milano, Milan, Italy
Interests: geodynamics; structural geology; numerical modeling

Prof. Dr. Jean-Marc Lardeaux

E-Mail Website
Guest Editor

Géoazur-Université Côte d’Azur, Nice, France
Interests: variscan and alpine orogens; metamorphic petrology; geochronology

Special Issue Information

Dear Colleagues,

The Alps represent a unique natural laboratory for studying the effect of superposed Wilson cycles. Although the Alpine collision has deeply affected the lithosphere of European and Adria plates, signatures of pre-Alpine evolution can be found in the Alps, from the periphery to the axial part of the chain. Magmatic, sedimentary, and metamorphic remnants diffusely preserved in the Alpine lithosphere have been repeatedly involved in active margin scenery since Cambro-Ordovician times. These remnants indicate a long-lasting history characterized by subduction and collision, post-collisional events, lithosphere extension, and rifting, allowing the formation and destruction of supercontinents and oceans.

The challenge is reconstructing the tectonic evolution at plate scale, starting from the small-scale structural, igneous, metamorphic, and sedimentary imprints preserved in the pre-Alpine relicts. Given the complexity of this trial, fundamental tools are the production of detailed structural maps, meso- and microstructural analysis, thermobarometric estimates, geochronology, and numerical modeling.

In this Special Volume of Minerals, we encourage the submission of contributions aimed at reconstructing the pre-Alpine history of the lithosphere of the Alps. Works at different scales of investigation and concerning structural and geological mapping, meso- and microstructural analyses, petrologic and metamorphic evolution, geochronologic interpretation, and numerical modeling are welcome.

Dr. Manuel Roda
Prof. Dr. Jean-Marc Lardeaux
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Minerals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

alpine lithosphere
metamorphic evolutions
numerical modeling
pre-alpine history
structural geology
variscan cycle
variscan–alpine transition

Published Papers (4 papers)

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Research

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17 pages, 16961 KiB

Open AccessArticle

Metasomatism by Boron-Rich Fluids along Permian Low-Angle Normal Faults (Central Southern Alps, N Italy)

by Stefano Zanchetta, Sofia Locchi, Gregorio Carminati, Manuel Mancuso, Chiara Montemagni and Andrea Zanchi

Minerals 2022, 12(4), 404; https://0-doi-org.brum.beds.ac.uk/10.3390/min12040404 - 25 Mar 2022

Cited by 3 | Viewed by 2030

Abstract

Low-Angle Normal Faults (LANFs) represent in the central Southern Alps area (N Italy) the main structures along which the Variscan basement is in contact with the Upper Carboniferous-Permian volcanic-sedimentary succession. Tourmalinites frequently occur along LANFs, usually replacing former cataclasites. The mineralogy and chemical composition of tourmalinites point to a metasomatic origin. LANFs, together with high-angle faults, controlled the opening of the Permian Orobic Basin and likely acted as a preferred pathway for hydrothermal fluids that triggered the Boron-metasomatism. Along the Aga-Vedello LANF, tourmalinites appear to have formed after the cessation of fault activity, as no brittle post-metasomatism deformation overprint has been observed. These relationships suggest that the circulation of B-rich fluids occurred after the opening of the Orobic Basin that is broadly constrained to the Early Permian. At the same time, ca. 285–270 Ma, a strong magmatic activity affected all the Southern Alps, ranging in composition from mafic to acidic rocks and from intrusions at deep crustal levels to effusive volcanic products. The Early Permian magmatism was likely the source of the late-stage hydrothermal fluids that formed the tourmalinites. The same fluids could also have played a significant role in the formation of the Uranium ore deposit of the Novazza-Vedello mining district, as the ore bodies in the Vedello valley are concentrated along the basement-cover contact. Full article

(This article belongs to the Special Issue Structural and Metamorphic Evolutions of the Pre-Alpine Lithosphere of the Alps)

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30 pages, 19881 KiB

Open AccessArticle

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

by Michele Zucali, Luca Corti, Manuel Roda, Gaetano Ortolano, Roberto Visalli and Davide Zanoni

Minerals 2021, 11(12), 1421; https://0-doi-org.brum.beds.ac.uk/10.3390/min11121421 - 15 Dec 2021

Cited by 6 | Viewed by 2293

Abstract

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. Full article

(This article belongs to the Special Issue Structural and Metamorphic Evolutions of the Pre-Alpine Lithosphere of the Alps)

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20 pages, 6184 KiB

Open AccessArticle

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

by Marco Filippi, Maria Iole Spalla, Nicola Pigazzini, Valeria Diella, Jean-Marc Lardeaux and Davide Zanoni

Minerals 2021, 11(10), 1124; https://0-doi-org.brum.beds.ac.uk/10.3390/min11101124 - 13 Oct 2021

Cited by 6 | Viewed by 2357

Abstract

Multiscale structural analysis is 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 Permian age limit on the pre-Alpine tectono–metamorphic 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. Full article

(This article belongs to the Special Issue Structural and Metamorphic Evolutions of the Pre-Alpine Lithosphere of the Alps)

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Review

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29 pages, 9196 KiB

Open AccessReview

Petrochronology of Monazite-Bearing Garnet Micaschists as a Tool to Decipher the Metamorphic Evolution of the Alpine Basement

by Bernhard Schulz

Minerals 2021, 11(9), 981; https://0-doi-org.brum.beds.ac.uk/10.3390/min11090981 - 09 Sep 2021

Cited by 4 | Viewed by 2001

Abstract

Garnet-bearing metapelites in the Helvetic and Austroalpine pre-Mesozoic polymetamorphic basement are characterised by pressure-temperature path segments reconstructed by microstructurally controlled geothermobarometry, and the Th-U-Pb monazite age distribution pattern revealed by the electron probe microanalyser (EPMA). In the Helvetic Aiguilles Rouges Massif and the Austroalpine Oetztal-Stubai basement to the NW an Ordovician-to-Silurian high temperature event preceded a pressure-dominated Carboniferous metamorphism. In the Austroalpine basement units to the south of the Tauern Window, the maximal pressures of the Carboniferous amphibolite-facies metamorphism range from 12 to 6 kbar. The decompressional P-T path segments signal a transition to low pressure conditions. A subsequent high pressure overprint is restricted to the Prijakt Subgroup unit in the Schobergruppe and documented by Cretaceous monazite crystallisation at 88 ± 6 Ma. In the Austroalpine Saualpe basement to the SE, a distinct early Permian metamorphism which started at low pressures of ~4 kbar/500 °C and reached maximal 6 kbar/600–650 °C predated the intrusion of Permian pegmatites. Permian monazite crystallised in line with the intrusion of pegmatites. Corona microstructures around the Permian monazites indicate retrogression previous to a Cretaceous high pressure metamorphism. That way, pressure-temperature-time paths resolve the spatial and temporal evolution in the polymetamorphic Alpine basement prior to the Tertiary collision. Full article

(This article belongs to the Special Issue Structural and Metamorphic Evolutions of the Pre-Alpine Lithosphere of the Alps)

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