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)
Page address... http://larecc.geoloweb.ch/fr/index.php?page=diplome_4 .......... Printed the 20.09.2021 at 16:25

3) Thermobarometry 4) Aluminosilicate-bearing quartz veins 5) Cartography

Distribution map of Knauern - Klein 1976
Distribution map of Knauern after Klein 1976
(Subpennic map modified after Spicher 1972)

An important part of this study focused on the kinematic and metamorphic significance of the aluminosilicates* veins within the framework of the alpine evolution. These veins are present in the metasediments* and are named Knauern* according to Keller (1968) [reference].

They have already been described by the works of Preiswerk (1918) [reference], Keller (1968) [reference] and Klein (1976) [reference].

As shown in the previous page, thermometry* by oxygen isotope* on quartz-kyanite pair in veins and surrounding metapelites* revealed concordant temperatures with those obtained by conventional thermobarometry* (620 to 720°C according to method and calibration of Sharp (1992, [reference], 1995 [reference])).

This confirms that these veins were formed during peak of metamorphism* (maximum of temperature) as suggested by our structural* study. The texture* analysis in veins demonstrate andalusite formation after retromorphosis of kyanite (see figures on the left and hereunder).

Retromorphosis of Ky in And
Centimetric cristal of kyanite partially retromorphosed in andalusite
, shape of andalusite crystal (on the right, rosa) conserve the tabluar form of kyanite (on the left, blue).

And blast with Ky inclusions
Monocristal of automorphic andalusite with inclusions of kyanite;
this last one can be sometimes deformed

Quartz-Andalusite pair in veins yielded temperatures comparable (640 to 760 °C) with those given by the pair quartz-kyanite in the same samples. Andalusite not being stable at these temperatures for the pressure conditions of metamorphic peak, the isotopic composition of this mineral may have been inherited from kyanite at the time of the polymorphic* transformation. Isotopic compositions of quartz and kyanite in the veins are comparable with those of the surrounding metapelites. It thus confirms that crystallization in these veins results from a local re-mobilisation of the material, shown by the mineralogical correlation between the aluminosilicate-bearing quartz veins and their surrounding* rock.
Clic here for more information on these veins

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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