Xav & Jul

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Photos - serie 1

1) Introduction 2) Structural Study 3) Thermobarometry

The tectonic* evolution of the area is divided into five successive deformation phases (see 3D sketch on the right and table at the bottom of the page).

Geological cross section
E-W profile of the studied field
Low resolution || High resolution

3D structural bloc
Bloc diagram representing various deformation phases
Low resolution || High resolution

Fissure de tension à AlSi (Knauern)
Example of Knauern, tension gashes with kyanite and/or andalusite

The first two observed phases D1 and D2 form isoclinal* folds and are related to overthrusting movement* towards the N-NW as part of the emplacement of the Simano nappe*. D2 is responsible for the main schistosity* and N-S main lineation* in all lithologies*.

D3 causes the opening of tension gashes* and the crystallization of the tension gashes (also known as "Knauern*"), and is related to top-North shearing. This phase is contemporary of the Tertiary* Barrovian* peak of metamorphism* (peak of temperature, see next page) in amphibolites facies*, which is marked by the assemblage* kyanite, garnet and staurolite in metapelites* and hornblende (tschermakite), plagioclase and garnet or biotite in amphibolites*.

The D4 phase of West vergent* transverse folding* give rise to the dominant fold structures in the studied area, including the great Lareccio anticline*. This fourth phase is at the origin of a new coarse schistosity S4, which develops in the hinges* of the great fold structures.

This D4 phase occurs always in amphibolite facies and shows a deflection of the major lower Pennine* unities towards W during the tectonic exhumation* event.

The last D5 phase causes a coarse vertical crenulation* due to vertical shortening during last stage of the ductile deformation history.

Postschistosity folding P4
Example of P4 (Larecc's folding, "similar" type)

Metamorphic isograds - Frey & Mählmann 1999
Metamorphism isograds in the Lepontine Alps
(from Frey & Mählmann 1999 [reference]) showing a regular increase of metamorphic* grad from N to S in the
Lepontine Alps*. The studied field is marked by a black star

Tab. cristallisation-deformation
Tabel of different deformations observed at Alpe Larecc. Aluminosilicate-bearing quartz veins (veins "AbQ") belong to the third deformation phase, which precedes transversal folding phase of Larecc-Maggia. Click here or on table to get more details on the relations between deformation and crystallisation of minerals. Sn = schistosity of n-th order. Fn = fold, Ln = lineation. N,W,S = North, West, South.

1) Introduction | 2) STRUCTURAL | 3) Thermobarometry | 4) Tension gashes | 5) Cartography | Bibliography | Thanks
Aluminosilicate-bearing veines: 4.1) Mineralogy | 4.2) Structure | 4.3) Examples | 4.4) Formation

Info on copyright || Download the abstract | the publication (PDF)

Photo - serie 2

Uni Lausanne || Geology 2003-2005 © Xavier Maeder & Julien Allaz
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Created: 10th May 2003
Last update: 3rd March 2012