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Illite (KI) and chlorite (AI) "crystallinity" indices as a constraint for the evolution of the external Brianconnais Front in western Ligurian Alps (NW Italy)

Fabrizio Piana, Stefano Battaglia, Carlo Bertok, Anna D'Atri, Alessandro Ellero, Leonardo Leoni, Luca Martire and Elena Perotti
Illite (KI) and chlorite (AI) "crystallinity" indices as a constraint for the evolution of the external Brianconnais Front in western Ligurian Alps (NW Italy)
Italian Journal of Geosciences (October 2014) 133 (3): 445-454

Abstract

Analyses of illite (KI) and chlorite (AI) "crystallinity" indices, mainly from Cretaceous to upper Eocene-lower Oligocene clay-rich formations, have been performed to constrain the metamorphic history of Brianconnais, Dauphinois/Provencal, and Western Ligurian flysch tectonic units at the Ligurian-Maritime Alps junction. The illite and chlorite mineralogical parameters point to very low-grade conditions for both the Brianconnais and Dauphinois/Provencal units, characteristic of the middle anchizonal grade. Also some tectonic slices of Western Ligurian flysch involved in the major transpressive shear zones developed along the External Brianconnais front share the same metamorphic grade as the Brianconnais and Dauphinois/Provencal units. Conversely the S. Remo-M. Saccarello unit, another Western Ligurian flysch unit overthrust at the top of the tectonic stack of the Western Ligurian Alps, underwent only diagenetic conditions. This shows that: a) in Western Ligurian Alps no significative change of metamorphic grade occurs across the External Brianconnais Front and thus the Brianconnais and Dauphinois/Provencal units were parts of a single foreland fold-and-thust-belt; b) Western Ligurian flysch units, although referable to a common palaeogeographic Ligurian domain, occur in two different tectonic settings: some units were placed along the European continental margin since before the beginning of Alpine tectonics and later on, from the Oligocene onwards, were involved and intensively sheared within transpressive shear zones along the External Brianconnais front; other units, such as the S. Remo-M. Saccarello unit, show a very different thermal history consistent with a shallower crustal path and an emplacement at the top of the tectonic stack in a final stage of the contractional regime.


ISSN: 2038-1719
EISSN: 2038-1727
Coden: BOGIAT
Serial Title: Italian Journal of Geosciences
Serial Volume: 133
Serial Issue: 3
Title: Illite (KI) and chlorite (AI) "crystallinity" indices as a constraint for the evolution of the external Brianconnais Front in western Ligurian Alps (NW Italy)
Affiliation: CNR, Istituto di Geoscienze e Georisorse, Turin, Italy
Pages: 445-454
Published: 201410
Text Language: English
Publisher: Societa Geologica Italiana, Rome, Italy
References: 38
Accession Number: 2014-105280
Categories: Igneous and metamorphic petrologyStructural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, geol. sketch maps
N44°15'00" - N44°40'00", E07°45'00" - E08°45'00"
Secondary Affiliation: Universita di Torino, ITA, ItalyUniversita di Pisa, ITA, Italy
Country of Publication: Italy
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Societa Geologica Italiana. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201452
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