On the "root zone" of the Alpine nappes in the Ticino area (Ivrea Zone, Insubric line and gneisses of the Southern Steep

Belt): Geometry and kinematics

Stefan M. Schmid

84th CONVENTION 2017 Ascona, Switzerland, Monte Verità, June 17–19, 2017

Livo gorge near Lake Como View from Losone towards Arcegno

S N S N

OROGEN-SCALE

Austroalpine

Southern Alps

The Insubric line; part of the Periadriatic line

Main activity of the Insubric Line: 32-20 Ma. The eastern segments (Pustertal- Gailtal- and Balaton-lines) are also active after 20 Ma, when the

Periadriatic line became offset by the Giudiarie line the Eastern Alps became laterally extruded to the east.

200 km

140 km

103 km 45 Ma 35 Ma

25 Ma 0 Ma

reconstruction for the last 45 Ma after Schmid et al. (2017), Europe fixed

estimate of the amount of dextral strike slip, based on the reconstruction of the movement of the Ivrea mantle wedge (green) for the last 35 Ma: 140 km

Estimate of the amount of dextral strike slip

Schmid et al. 2017

Estimate of backthrusting along the Insubric Line

22 km

Schmid et al. 2004

Large amounts of exhumation by retro-thrusting and Subsequent erosion restricted to the Lepontine dome

Oberhänsli et al. 2004

The Lepontine dome in map view

Simano & Leventina- Lucomagno

M. Rosa Bellinzona- Dascio

Zermatt- Saas Fee

Gotthard nappe

Schmid et al. 2017

limit amphibolite

grade

The Lepontine dome in profile view

Schmid et al. 2017

Ivrea Zone

Ticino & Lombardian S. Alps

S. Alps preserve a passive margin

Granulite facies mafics Granulite facies metapelites

Passive margin formation exhumed Ivrea zone

Age of peak-T: Permian!!!!

Schmid et al. 1989

LOCAL GEOLOGY, OUTCROPS, THIN SECTIONS

Canavese Line (eastern branch of Insubric line) in Valle d’Ossola

NW SE

Ivrea Zone Sesia Zone

Zingg et al. 1990

SE NW

SE NW

SOUTHERN ALPS CENTRAL ALPS

CENTRAL ALPS SOUTHERN ALPS

Insubric line near Ascona

N S

Arcegno

Losone

Ivrea Zone Sesia-derived

mylonites

Canavese Mesozoic

Sesia Zone P.-L. Ocean Zerm.-Saas

Zone

Monte Rosa nappe

N S Ivrea-derived mylonites

2 km

Schmid et al. 1987 & 1989

The northern part of the mylonite belt records steep lineations, indicating back- thrusting. The southern part of the mylonite belt records sub- horizontal lineations, Indicating dextral strike slip

subhorizontal lineations = strike slip

down-dip lineations = back-thrusting

backthrusting and strike slip displacements

Fault rocks at the Insubric line 1

mafic rocks Ivrea Zone paragneisses Ivrea Zone

pseudotachylite

cataclasite pre-Alpine fabric

Ivrea-derived mylonite

Fault rocks at the Insubric line 2

mylonitized Mesozoic limestone Sesia-derived mylonites

lineations

sheath fold

sigma clasts

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2

3$

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our hotel

Grotto Zelinda

tectonic map of the Arcecno area and excursion day 2

unpublished

Monte Rosa

Insubric mylonites

Sesia

Ivrea

Onsermone zone

(Antigorio)

Belinzona-Dascio zone (Valaisan?)

Maggia

Belinzona-Dascio zone

Cima Lunga (Adula)

Maggia (Vogorno)

Maggia (Cocco gneiss)

Strona Ceneri

Simano (490Ma granite gneiss)

Lavertezzo  

Zerm.-Saas Fee

southern part of the Lepontine dome

Berger & Merolli 2005

foliations and lineations

mostly Eduard Wenk unpublished compiled by S. Schmid

lineations foliations

foliations, lineations & tectonic map

Simano  nappe  

Bellinzona-­‐Dascio  Zone  

Insubric  line  

Profile across the southernmost Lepontine dome

Geology of Switzerland Guide Book 1980

2.  stop   1.  stop  

Polyphase folding in the Lepontine dome at Lavertezzo