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The pre-Alpine tectonic history of the Austroalpine continental basement in the Valpelline Unit (western Italian Alps)

Paola Manzotti and Michele Zucali
The pre-Alpine tectonic history of the Austroalpine continental basement in the Valpelline Unit (western Italian Alps)
Geological Magazine (January 2013) 150 (1): 153-172

Abstract

The Valpelline unit is a large slice of continental crust constituting the Austroalpine Dent Blanche nappe (NW Italy). The pre-Alpine evolution of this unit holds important clues about the Palaeozoic crustal structure at the northern margin of the Adria continent, about the history of rifting in the Alpine region, and thus about the thermomechanical conditions that preceded the Alpine convergent evolution. Several stages of the deformation history and of partial re-equilibration were identified, combining meso- and micro-structural analyses with thermobarometry. Reconstructed pre-Alpine P-T-t-d paths demonstrate that the Valpelline unit experienced an early stage at pressures between 4.5 and 6.5 kbar followed by migmatite formation. A subsequent stage reached amphibolite to granulite facies conditions. This stage was associated with the development of the most penetrative fabrics affecting all of the Valpelline lithotypes. The pre-Alpine evolution ended with a weak deformation associated with a local mineral-chemical re-equilibration under greenschist facies conditions at nearly equal 4 kbar and T < 450 degrees C. A Permo-Mesozoic lithospheric extension is thought to be responsible for asthenosphere upwelling, thereby causing high temperature metamorphism at medium pressure and widespread partial melting, which led to upper crustal magmatic activity.


ISSN: 0016-7568
EISSN: 1469-5081
Coden: GEMGA4
Serial Title: Geological Magazine
Serial Volume: 150
Serial Issue: 1
Title: The pre-Alpine tectonic history of the Austroalpine continental basement in the Valpelline Unit (western Italian Alps)
Affiliation: Universitaet Bern, Institut fuer Geologie, Bern, Switzerland
Pages: 153-172
Published: 201301
Text Language: English
Publisher: Cambridge University Press, London, United Kingdom
References: 73
Accession Number: 2013-021020
Categories: Structural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, geol. sketch map
N44°49'60" - N46°40'00", E08°00'00" - E11°13'00"
Secondary Affiliation: Universita degli Studi di Milano, ITA, Italy
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Cambridge University Press. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201314
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