Tectonics of the Simplon massif and Lepontine gneiss dome: deformation structures due to collision between the underthrusting European plate and the Adriatic indenter |
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| Authors: | Albrecht Steck |
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| Institution: | (1) Institute of mineralogy and geochemistry, Anthropole, University of Lausanne, CH-1015 Lausanne, Switzerland |
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| Abstract: | This study presents a review of published geological data, combined with original observations on the tectonics of the Simplon
massif and the Lepontine gneiss dome in the Western Alps. New observations concern the geometry of the Oligocene Vanzone back
fold, formed under amphibolite facies conditions, and of its root between Domodossola and Locarno, which is cut at an acute
angle by the Miocene, epi- to anchizonal, dextral Centovalli strike-slip fault. The structures of the Simplon massif result
from collision over 50 Ma between two plate boundaries with a different geometry: the underthrusted European plate and the
Adriatic indenter. Detailed mapping and analysis of a complex structural interference pattern, combined with observations
on the metamorphic grade of the superimposed structures and radiometric data, allow a kinematic model to be developed for
this zone of oblique continental collision. The following main Alpine tectonic phases and structures may be distinguished:
| 1. |
NW-directed nappe emplacement, starting in the Early Eocene (~50 Ma); |
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W, SW and S-verging transverse folds; |
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transpressional movements on the dextral Simplon ductile shear zone since ~32 Ma; |
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formation of the Bergell – Vanzone backfolds and of the southern steep belt during the Oligocene, emplacement of the mantle
derived 31–29 Ma Bergell and Biella granodiorites and porphyritic andesites as well as intrusions of 29–25 Ma crustal aplites
and pegmatites;
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| 5. |
formation of the dextral discrete Rhone-Simplon line and the Centovalli line during the Miocene, accompanied by the pull-apart
development of the Lepontine gneiss dome – Dent Blanche (Valpelline) depression.
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It is suggested that movements of shortening in fan shaped NW, W and SW directions accompanied the more regular NW- to WNW-directed
displacement of the Adriatic indenter during continental collision.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Editorial Handling: Stefan Bucher |
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| Keywords: | :" target="_blank">: Alpine tectonics Simplon massif nappe tectonics transpression continental collision |
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