Diploma Thesis (M.Sc. equivalent) of Xavier MAEDER and Julien ALLAZ:
Tectonic and metamorphic evolution of Simano nappe at Alpe Larecc (Tessin, CH) © 2003-2007, Uni. Lausanne (Switzerland).
Contacts: Xavier MAEDER (maederx@uni-mainz.de) or Julien ALLAZ (jallaz@geo.unibe.ch)
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Back to entry 1) Introduction 2) Structural Study

This diploma thesis focused on tectonic* and metamorphism* of the Alpe Larecc (Val Lavizzara, North of Ticino, Switzerland) around the main Lareccio anticline* (= Verzasca anticline), at the limit between pre-Mesozoic* metasediments* of the Campo Tencia unit and the Verzasca gneiss* complex on Simano nappe.

Metasediments are mainly micaschists* (figure on the left) and paragneiss*. Besides both micas (biotite and muscovite), plagioclase (5-25% anorthite) and quartz (ubiquist in those lithologies), garnet, kyanite and staurolite are also often associated. In some particular lithologies*, garnet and/or staurolite can form centimetric porphyroblasts*. The metasediment layers with porphyroblasts are irregular from millimeter- to decameter-size thickness. The sediment are composed of an alternation of argilous (micas-rich) and detritics (rich in quartzo-feldspathic material) deposits.

Thin section of micaschist Thin section of an amphibolite with associated paragneiss
Photographies of typical thin section of...
Micaschist with Garnet + Staurolite + Kyanite Amphibolite and paragneiss associated

Amphibolites* (in its broad sens, figure on the right) are composed of alternation of massive amphibolites (in the strict sens with often more than 75% amphibole) and paragneiss with amphibole (right figure). The amphibolite (strict sens) shows a mineral assemblage* with green hornblend (tschermakite), garnet, plagioclase (15-45% anorthite) and biotite. The local retromorphosis* of those rocks lead to the formation of epidote-calcite-chlorite assemblage.

Finally, augen gneiss* (figure below) are formed of feldspars porphyroblasts (plagioclases [8-25% anorthite] and K-feldspars), quartz and two micas (muscovite and biotite). In the border, porphyroblasts tend to disappear, leaving place to a leucocratic* facies, called border facies (light rose in the geological map). This facies is formed by a top to the North shearing* linked to the nappes* emplacement (see next page).
Augen gneiss with quartz, plagioclases and potash feldspars

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

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