Platta-Ophiolith

Representation and status

Color CMYK

(38%,0%,25%,37%)

Color RGB

R: 100 G: 160 B: 120

Rank

lithostratigraphic unit

Validity

Unit is in Use

Nomenclature

Deutsch

Platta-Ophiolith

Français

Ophiolite du (Piz) Platta

Italiano

Ofiolite del (Piz) Platta

English

Platta Ophiolite

Origin of the Name

Piz Platta (GR)

Historical Variants

Ophiolithe vom Typus der Platta-Decke (Büchi & Trümpy 1976), Platta-Ophiolithe (Spillmann 1993), Ophiolites [of the Platta nappe] (Manatschal & Nievergelt 1997), Ophiolites of the Piz Platta region

Hierarchy and sequence

Subordinate units

• Metabasalt der Platta-Decke
• Metagabbro der Platta-Decke
• Serpentinit der Platta-Decke

Age

Age at top

• Kimmeridgian

Age at base

• Callovian

Dating Method

161 +/-1 Ma (Schaltegger et al. 2002, Peters & Dietrich 2008)

Geography

Geographical extent

Serpentinit, Grabbro, Basalt und Grünschiefer, mit untergeorneten Sedimenten.

Palaenography and tectonic

Paleogeography

Piemont Basin

Tectonic unit (resp. main category)

• Platta

Kind of protolith

• ophiolitic

Metamorphism

monocyclic

Metamorphic facies

• greenschist facies (epizone)

Note on metamorphism

Ultrabasic rocks are represented by lizardite-chrysotile-serpentinite north of Bivio and antigorite bearing lizardite-chrysotile-serpentinite south of Bivio, indicating an increase in Alpine metamorphism from north to south (Trommsdorff & Evans 1974, Trommsdorff 1983).

References

Definition

Dietrich Volker (1969) : Die Ophiolithe des Oberhalbsteins (Graubünden) und das Ophiolithmaterial der ostschweizerischen Molasseablagerung ein petrographischer Vergleich. Diss. ETHZ Nr.4397, 179 S.

Definition

Manatschal Gianreto, Nievergelt Peter (1997) : A continent-ocean transition recorded in the Err and Platta nappes (Eastern Switzerland). Eclogae geol. Helv. 90/1, 3-27

p.8: Ophiolites [of the Platta nappe]

Massive basalts, pillow lava and breccia and hyaloclastites represent the extrusive part of the ophiolite suite of the Platta nappe (Steinmann 1905, Cornelius 1935. Dietrich 1969. 1970). With higher strain and grade of metamorphism towards the south, the primary extrusive structures are gradually obliterated (Dietrich 1969). Gabbro is rare and is intrusive together with basaltic dikes in serpentinite. Some gabbros are undeformed (e.g. Val Natons). whereas others are strongly foliated and exhibit a clear stretching lineation and asymmetric fabrics indicating non-coaxial shear under high-temperature conditions (at least 400 to 500 C). Plagioclase and pyroxene ribbons suggest crystal plastic deformation mechanisms, active during the deformation of these rocks. Since Alpine metamorphism in the area is only of greenschist facies (Trommsdorff 1983), a pre-Alpine age for these gabbroic mylonites is strongly suggested.

Ultrabasic rocks are represented by lizardite-chrysotile-serpentinite north of Bivio and antigorite bearing lizardite-chrysotile-serpentinite south of Bivio, indicating an increase in Alpine metamorphism from north to south (Trommsdorff & Evans 1974, Trommsdorff 1983). Unaltered relics of péridotites were not described, but from microscopic as well as from geochemical data spinel lherzolites and harzburgites are presumed to be the protoliths of the serpentinites (Dietrich 1969, Trommsdorff & Evans 1974. Burkhard & O'Neil 1988).