Fulltext

Tectonics of the Simplon massif and Lepontine gneiss dome: deformation structures due to collision between the underthrusting European plate and the Adriatic indenter

Steck, Albrecht

In: Swiss Journal of Geosciences, 2008, vol. 101, no. 2, p. 515-546

Ajouter à la liste personnelle
    Titre
    • Tectonics of the Simplon massif and Lepontine gneiss dome: deformation structures due to collision between the underthrusting European plate and the Adriatic indenter
    Auteur
    • Steck, Albrecht. Institute of mineralogy and geochemistry, Anthropole, University of Lausanne, CH-1015, Lausanne, Switzerland
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Swiss Journal of Geosciences, 2008, vol. 101, no. 2, p. 515-546. SP Birkhäuser Verlag Basel
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:316067
    Summary
    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 50Ma 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 (~50Ma); 2. W, SW and S-verging transverse folds; 3. transpressional movements on the dextral Simplon ductile shear zone since ~32Ma; 4. formation of the Bergell - Vanzone backfolds and of the southern steep belt during the Oligocene, emplacement of the mantle derived 31-29Ma Bergell and Biella granodiorites and porphyritic andesites as well as intrusions of 29-25Ma crustal aplites and pegmatites; 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. 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