Structural evolution of the contact between two Penninic nappes (Zermatt-Saas zone and Combin zone, Western Alps) and implications for the exhumation mechanism and palaeogeography

• Published in: International journal of earth sciences : Geologische Rundschau Vol. 96; no. 2; pp. 229 - 252
• Main Authors: Pleuger, Jan, Roller, Sybille, Walter, Jens M., Jansen, Ekkehard, Froitzheim, Nikolaus
• Format: Journal Article
• Language: English
• Published: Berlin Springer Nature B.V 01.04.2007
• Subjects: Geology; Ocean basins; Paleoceanography; Plate tectonics
• ISSN: 1437-3254; 1437-3262
• DOI: 10.1007/s00531-006-0106-6

The boundary zone between two Penninic nappes, the eclogite-facies to ultrahigh-pressure Zermatt-Saas zone in the footwall and the blueschist-facies Combin zone in the hanging wall, has been interpreted previously as a major normal fault reflecting synorogenic crustal extension. Quartz textures of mylonites from this fault were measured using neutron diffraction. Together with structural field observations, the data allow a refined reconstruction of the kinematic evolution of the Pennine nappes. The main results are: (1) the contact is not a normal fault but a major thrust towards northwest which was only later overprinted by southeast-directed normal faulting; (2) exhumation of the footwall rocks did not occur during crustal extension but during crustal shortening; (3) the Sesia-Dent Blanche nappe system originated from a continental fragment (Cervinia) in the Alpine Tethys ocean, and the Combin zone ophiolites from the ocean basin southeast of Cervinia; (4) out-of-sequence thrusting played a major role in the tectonic evolution of the Penninic nappes.[PUBLICATION ABSTRACT] Erratum DOI: 10.1007/s00531-007-0197-8