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Mountain building processes: a combined field and experimental approach

English title Mountain building processes: a combined field and experimental approach
Applicant Pfiffner Adrian
Number 137530
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 01.10.2011 - 30.09.2012
Approved amount 56'692.00
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Keywords (5)

Alpine geology; Mountain building; Penninic nappes; Structural geology; Nappe stacking

Lay Summary (English)

Lead
Lay summary

The geological processes leading to the formation of mountain chains include processes going on at depths of up to 30 km beneath the Earth's surface and process shaping the surface of the mountain chain. In this project we study these processes studying the rocks within the Alpine chain and comparing the evolving model to sandbox experiments we performed in the laboratory and numerical modeling.

Mountain building processes at depth involve the deformation of rock units in the contact zone of the collision of two continents. In this process packages of rocks , 1 - 5 km thick and 10 - 50 km long, are placed on top of each other. These packages, called nappes, are intensively deformed during the stacking. This stacking results in a direct uplift of the rocks above and thus the land surface. But thickening the crust of the mountain chain also leads to buoyant rise of the entire chain because of the low density of the crust in comparison to the denser mantle beneath. In the Alps the nappe stacks that formed at depth are now directly observable at the surface because many kilometers of rock layers were removed by erosion. This allows us to study the deformations going on during nappe stacking. Structural analysis will allow to unravel the sequence of deformation events. At critical places we wish to date the deformation features by dating minerals that formed during the event. Previous work on these nappe stacks did not separate between structures due to folding from those caused by faulting. Our analysis includes both and involves a quantitative assessment of the strains accumulated.

By studying the Suretta nappe (Graubünden) and the Bernhard nappe complex (Valais) we compare two units that had much in common regarding their geological history and are key units in regard to deep crustal nappe stacking. Our early results suggest that the geometry of the nappes is strongly controlled by pre-existing heterogeneities (Permo-Carboniferous graben fills). Their lateral discontinuity explains differences in cross-sectional geometry that hitherto had been overlooked because of simple projections along strike of the Alpine chain.

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Strain accumulation during basal accretion in continental collision – a case study from the Suretta nappe (eastern Swiss Alps).
Scheiber T. Pfiffner O.A. Schreurs G., Strain accumulation during basal accretion in continental collision – a case study from the Suretta nappe (eastern Swiss Alps)., in Tectonophysics.

Collaboration

Group / person Country
Types of collaboration
Isotope geology group/Institut für Geologie, Prof. K. Mezger Switzerland (Europe)
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Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved


Communication with the public

Communication Title Media Place Year
Media relations: print media, online media From the Ground up Research Media, Special issue of International Innovation: Disseminating science, research and techn International 01.10.2012

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)

Abstract

In the question of building a mountain belt we intend to study the processes governing the (rock and surface) uplift responsible for the build-up of a mountain range. This will include the growth of large-scale antiformal structures (basement uplifts) and imbricate thrusting of crystalline basement nappes as observed in collisional orogens. In this study we concentrate on the Penninic basement nappes in the Swiss Alps and intend to better understand the stacking of crustal units during continent-continent collision. To do so we analyse the strain state in the nappes and study the relation between folding and faulting in cross sections. Retrodeformation of the cross sections will highlight aspects of the evolution of these structures.
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