Skip to Main Content
Book Chapter

Exhumation and deformation history of the lower crustal section of the Valstrona di Omegna in the Ivrea Zone, southern Alps

By
S. Siegesmund
S. Siegesmund
1
Gottinger Zentrum Geowissenschaften, University of Göttingen
,
Goldschmidtstrasse 03, D–37077, Göttingen
(e-mail: ssieges@gwdg.de)
Search for other works by this author on:
P. Layer
P. Layer
2
Geophysical Institute, University of Alaska Fairbanks
,
Fairbanks, Alaska 99775
,
USA
Search for other works by this author on:
I. Dunkl
I. Dunkl
1
Gottinger Zentrum Geowissenschaften, University of Göttingen
,
Goldschmidtstrasse 03, D–37077, Göttingen
(e-mail: ssieges@gwdg.de)
Search for other works by this author on:
A. Vollbrecht
A. Vollbrecht
1
Gottinger Zentrum Geowissenschaften, University of Göttingen
,
Goldschmidtstrasse 03, D–37077, Göttingen
(e-mail: ssieges@gwdg.de)
Search for other works by this author on:
A. Steenken
A. Steenken
3
Instituto de Geociências, Universidade de São Paulo
,
Rua do Lago 562, Cidade Universitária, 05508-080 - São Paulo, SP-
Brazil
Search for other works by this author on:
K. Wemmer
K. Wemmer
1
Gottinger Zentrum Geowissenschaften, University of Göttingen
,
Goldschmidtstrasse 03, D–37077, Göttingen
(e-mail: ssieges@gwdg.de)
Search for other works by this author on:
H. Ahrendt
H. Ahrendt
1
Gottinger Zentrum Geowissenschaften, University of Göttingen
,
Goldschmidtstrasse 03, D–37077, Göttingen
(e-mail: ssieges@gwdg.de)
Search for other works by this author on:
Published:
January 01, 2008

Abstract

The Ivrea Zone (southern Alps) is one of the key regions interpreted as exposing a section of the lower continental crust and was the subject of several review-type articles. The Ivrea–Verbano Zone was rotated into an upright position along the Insubric mylonite belt. In the southeast, this unit is in contact with the Strona Ceneri Zone, which is interpreted as upper continental crust crossing the Permian Cossato–Mergozzo–Brissagio Line (CMB Line). The CMB mylonites are locally overprinted by the mylonites and cataclasites of the Pogallo Line, which was active during the Jurassic. In addition, the sinistral, steeply inclined Rosarolo shear zone was active over a long time span from the ductile into the brittle field, i.e. from the Early Permian (high-temperature ultra-mylonites) to the Neo-Alpine basic dykes and pseudotachylites. The high-temperature mylonites accommodated crustal extension and may be related to normal faults generated by magmatic underplating. The reactivation at different crustal levels during exhumation and tilting is documented by strain increments at decreasing P/T conditions. Its present subvertical orientation was attained during the Neo-Alpine deformation. Constraints on its exhumation history are based on new 40Ar/39Ar hornblende ages, K–Ar biotite ages and zircon fission-track data along the NE–SW trending Valstrona section. A re-interpretation of existing U–Pb monazite ages is included, based on a higher closure temperature for monazite. The oldest monazite ages are observed in proximity to the Pogallo Line (c. 292 Ma). Heat input by mafic intrusions was sufficient to reset the U–Pb monazite system, as is evidenced by the youngest ages in the vicinity of the Insubric Line. The re-interpretation favours the hypothesis that the oldest monazite ages are the result of complete resetting by a Permian thermal event. The 40Ar/39Ar hornblende ages and K–Ar biotite ages document the cooling after Permian heating. Roughly parallel age progressions decrease from the Pogallo Line (hornblende: 271 Ma vs. biotite: 227 Ma) towards the Insubric Line (hornblende: 201 Ma vs. biotite: 156 Ma). Zircon fission-track ages run parallel to the biotite ages in the upper part of the profile, whereas towards the Insubric Line a significant deviation from the biotite age progression is attributed to tilting of the basement during the Oligocene. Zircon fission-track ages around 38 Ma are found close to the Insubric Line. No age offset, neither at the CMB nor at the Pogallo Line, is observed. This confirms the hypothesis that the Pogallo Line is an oblique normal fault, and that the CMB Line has accommodated only minor vertical displacement. The capture of the different cooling ages confirms the tilting of the Ivrea–Verbano Zone during the Neo-Alpine deformation and contradicts the tilting of the Ivrea–Verbano Zone during the Permian.

You do not currently have access to this article.

Figures & Tables

Contents

Geological Society, London, Special Publications

Tectonic Aspects of the Alpine-Dinaride-Carpathian System

S. Siegesmund
S. Siegesmund
University of Göttingen, Germany
Search for other works by this author on:
B. Fügenschuh
B. Fügenschuh
University of Innsbruck, Austria
Search for other works by this author on:
N. Froitzheim
N. Froitzheim
University of Bonn, Germany
Search for other works by this author on:
Geological Society of London
Volume
298
ISBN electronic:
9781862395466
Publication date:
January 01, 2008

GeoRef

References

Related

Citing Books via

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal