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Structure and evolution of an antiformal nappe stack (Aar massif, Central Alps): Formation of mechanical anisotropies and their bearing on natural risks

English title Structure and evolution of an antiformal nappe stack (Aar massif, Central Alps): Formation of mechanical anisotropies and their bearing on natural risks
Applicant Herwegh-Züger Marco
Number 132196
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geologie Universität Bern
Institution of higher education University of Berne - BE
Main discipline Geology
Start/End 01.10.2010 - 30.09.2013
Approved amount 249'301.00
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Keywords (5)

deformation; crystalline rocks; exhumation; shear zones; natural risks

Lay Summary (English)

Lead
Lay summary
The Aar massif and its sedimentary cover form an antiformal nappe stack, which evolved during a late stage of the Alpine orogeny. Particularly the crystalline rocks were affected by multistage deformation events, where initial structures formed already during the emplacement of magmatic rocks (Zentraler Aaregranit). These initial mechanical anisotropies, mainly shear zones, were reused and activated over and over again during the Alpine orogeny. Based on a combination of remote sensing and detailed fieldwork, this study will develop a 3D model of the shear zone geometry. In combination with microstructural analyses and age determination, the deformation processes involved in strain localization and their contribution to the formation of the large-scale structures will be unraveled.Based on these extensive investigations, we expect to gain new important knowledge on the deformation sequence, mechanical behavior and the resulting effect on strain localization during the evolution of an antiformal nappe stack. Besides these aspects of fundamental research, the project will also give new insights into socially relevant questions like the geometry of fluid pathways (geothermal energy), the role of the exposed meachanical anisotropies in terms of natural risks (rock falls, landslides) and the potential of seismic activity during the formation of the shear zones.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
How is strain localized in a meta-granitoid, mid-crustal basement section? Spatial distribution of deformation in the central Aar massif (Switzerland)
Wehrens P., Baumberger R., Berger A., Herwegh M. (2017), How is strain localized in a meta-granitoid, mid-crustal basement section? Spatial distribution of deformation in the central Aar massif (Switzerland), in Journal of Structural Geology, 94, 47-67.
Deformation at the frictional-viscous transition: Evidence for cycles of fluid-assisted embrittlement and ductile deformation in the granitoid crust
Wehrens Philip, Berger Alfons, Peters Max, Spillmann Thomas, Herwegh Marco (2016), Deformation at the frictional-viscous transition: Evidence for cycles of fluid-assisted embrittlement and ductile deformation in the granitoid crust, in Tectonophysics, 693, 66-84.

Collaboration

Group / person Country
Types of collaboration
CSIRO Australia (Oceania)
- Research Infrastructure
Universität Kopenhagen Denmark (Europe)
- in-depth/constructive exchanges on approaches, methods or results
CSIRO & Curtin University Australia (Oceania)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
EGU2013 Poster Handling and quantifying uncertainty in geological 3D models: A methodological approach based on remote-sensing and field work (Roland Baumberger was first author) 07.11.2013 Vienna, Austria Wehrens Philip Chaim; Herwegh-Züger Marco;
Deformation, Rheology and Tectonics (DRT 2013) Poster Alpine re-activation of pre-existing anisotropies: details from a large-scale shear zone in the Aar massif (Central Alps) 16.09.2013 Leuven, Belgium Wehrens Philip Chaim; Herwegh-Züger Marco;
EGU 2013 Talk given at a conference Alpine re-activation of pre-Alpine structures: details from a large-scale shear zone in the Aar massif (Central Alps) 07.05.2013 Vienna, Austria Herwegh-Züger Marco; Wehrens Philip Chaim;
SGM 2012 Talk given at a conference Deformational evolution of the Aar Massif (Central Alps): From macro- to micro-scale 17.11.2012 Bern, Switzerland Wehrens Philip Chaim; Herwegh-Züger Marco;
EGU 2012 Poster Spatial distribution of quartz recrystallization microstructures across the Aar massif (MSc Max Peters was first author) 27.04.2012 Vienna, Switzerland Wehrens Philip Chaim; Herwegh-Züger Marco;
EGU 2012 Poster Large scale 3D geometry of deformation structures in the Aar massif and overlying Helvetic nappes (Central Alps, Switzerland) – A combined remote sensing and field work approach (Baumberger Roland was first author) 26.04.2012 Wien, Austria Herwegh-Züger Marco; Wehrens Philip Chaim;
EGU 2012 Poster Structural Evolution in the Aar Massif (Central Alps): First attempts of linking the micron- to the kilometer-scale 25.04.2012 Wien, A, Austria Wehrens Philip Chaim; Herwegh-Züger Marco;
Tektonik-Struktur- und Kristallingeologie (TSK) 2012 Poster Large scale 3D geometry of deformation structures in the Aar massif and overlying Helvetic nappes (Central Alps, Switzerland) – A combined remote sensing and field work approach; Baumberger Roland war Erstautor 30.03.2012 Kiel, Germany Herwegh-Züger Marco; Wehrens Philip Chaim;
Konferenz für Tektonik-Struktur- und Kristallingeologie (TSK) 2012 Poster Large scale 3D geometry of deformation structures in the Aar massif and overlying Helvetic nappes (Central Alps, Switzerland) – A combined remote sensing and field work approach (Roland Baumberger was first author) 30.03.2012 Kiel, D, Germany Herwegh-Züger Marco; Wehrens Philip Chaim;
Swiss Geoscience Meeting 2011 Zurich Talk given at a conference Spatial distribution of quartz recrystallization microstructures across the Aar massif (MSc Max Peters was first author) 12.11.2011 Zürich, Switzerland Wehrens Philip Chaim; Herwegh-Züger Marco;


Associated projects

Number Title Start Funding scheme
122143 Mountain building and basin formation processes: a combined experimental and field approach 01.10.2008 Project funding (Div. I-III)
126560 The role of Polymineralic Rocks in the Evolution of Shear Zones 01.12.2009 Project funding (Div. I-III)
144381 The role of sheet silicate-rich rocks during mountain building processes 01.01.2013 Project funding (Div. I-III)
66889 Grain growth in polyphase rocks under static and deformational conditions in nature and experiment 01.04.2002 Project funding (Div. I-III)
149385 Structure and evolution of an antiformal nappe stack (Aar massif, Central Alps): Formation of mechanical anisotropies and their bearing on natural risks 01.10.2013 Project funding (Div. I-III)
121578 A 4D Model of Neogene Exhumation in the Central Helvetic Alps 01.10.2008 Project funding (Div. I-III)
119878 Deformation mechanisms in naturally and experimentally deformed minerals and rocks (8) 01.04.2008 Project funding (Div. I-III)
109369 Rasterelektronenmikroskop Geologie Bern 01.02.2006 Project funding (Div. I-III)
169055 Structure and evolution of an antiformal nappe stack (Aar massif, Central Alps): Formation of mechanical anisotropies and their bearing on natural risks 01.10.2016 Project funding (Div. I-III)

Abstract

In the case of foreland fold and thrust belts, strain is strongly localized in thrust zones that are only active over certain time intervals before new thrusts are activated inducing a passive deformation of the older parts. In this way, nappes pile up in front of an orogen and nappe stacks evolve. Continued compression induces an up-doming of the entire tectonic sequence resulting in the formation of an antiformal nappe stack (e.g. Aar massif, central Alps; Tauern window, eastern Alps). Such deformation sequences encompass a heterogeneous strain distribution resulting in complex 3D pattern of high strain domains like shear and fault zones. Such a tectonic evolution often is characterized by the transition from thin- to thick-skinned tectonics involving the entire range from ductile (e.g., ‘soft’ rocks like sediments) to brittle (e.g. ‘hard’ rocks like low T deformation in crystalline rocks) deformation. Owing to the long lasting evolution of an antiformal nappe stack, the rocks undergo deformation at different crustal levels, provoking the reactivation of former mechanical anisotropies (brittle or ductile faults) as zones of weakness, which are re-used in a ductile or brittle manner (prograde vs retrograde metamorphic conditions) during subsequent deformation events. In this study, we will explore the geodynamic 3D evolution of the Aar massif and Helvetic nappe system as a prominent and very well exposed example of an antiformal nappe stack. As a great advantage, deformation occurred in both crystalline and sedimentary rocks allowing to evaluate the geometric, kinematic and mechanical evolution of deformation in these different rock types at a broad variety of scales (nm-kilometers). For this purpose, we plan to carry out three major project parts, each of them to be investigated by an individual PhD student:Part A: Quantitative investigation of the large- to meso-scale (km-m) strain localization pattern, its evolution in 3D and the resulting consequences for today’s geomorphology and natural risk potential.Part B: Unraveling of the deformation processes/mechanisms, their changes in time and their role on strain localization in the case of the deformed crystalline rocks of the Aar massif. Part C: Analysis of the interplay between deformation and fluid during the late stages of Alpine compression in the sedimentary rocks of the Helvetic nappe system. In a second step, the role of late mechanical anisotropies (faults, joints) in terms of the natural risk potential (rock fall, landslides) will be evaluated. The suggested proposal as a whole represents an integrated and interdisciplinary project, which links the deformation/microphysical processes at different former crustal levels with the large-scale situation. Besides new insights on the aforementioned topics, the entire project provides the great opportunity to study the role of spontaneous and short lived versus continuous long-lasting deformation particularly in light of potential indicators for aseismic versus seismic events. In this way, the study area will give new information on the deformation processes and associated structures as they may be active in the recent seismogenic zone inside the Aar massif and the Northalpine foreland.
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