2. Mineralogy – Petrology – Geochemistry - SWISS GEOSCIENCE ...

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Symposium 1: Structural Geology, Tectonics and Geodynamics
1.13
Structure of the Helvetic nappe system of the Swiss Alps and adjoining
France and Austria.
Pfiffner O. Adrian
Institut für Geologie, Universität Bern, Baltzerstr. 1+3, Bern (adrian.pfiffner@geo.unibe.ch)
A new structural map of the Helvetic nappe system at the scale 1:100’000 has been prepared in the course of the past
years based on a project initiated by John Ramsay in 1978. After revisions and expansion of the map area a digital version
is now available (Pfiffner et al. 2009). The map consists of 7 individual sheets, each with a cross section and its own legend
and . Considerable overlay between the map sheets help to facilitate lateral correlations. The map contains the traces of
faults as well as the axial surfaces of large-scale folds. Lithologic units have been kept simple and adapted to the scale of
the map.
The aim of the structural map series of the Helvetic zone is to show the lateral continuity of folds and thrusts, their spatial
orientations and mutual interference as well as to highlight the characteristics of the fold-and-thrust structures in
individual regions and units. The Helvetic zone, or nappe system, is subdivided into two zones with rather different structural
style, the Helvetic nappes proper and the underlying Infrahelvetic complex. The Helvetic nappes comprise allochthonous
sediments that were dislocated along a basal thrust fault over distances of several tens of kilometers. The Infrahelvetic
complex encompasses all units beneath the basal thrust of the Helvetic nappes. It consists of pre-Triassic crystalline
basement rocks and their autochthonous Mesozoic and Cenozoic sedimentary cover. The simplified map in Fig. 1 gives an
overview of the nappe systems and foreland basins of the Central Alps. The major basal thrusts of the Helvetic nappes as
well as the major transverse faults are also included along with the orientations of the fold axes of large-scale folds. As
example a cross section of the Helvetic nappe system in central Switzerland ranging from the Molasse Basin to the rear of
the Gotthard massif is shown in Fig. 2.
Fig. 1
Swiss Geoscience Meeting 2011
Platform Geosciences, Swiss Academy of Science, SCNAT