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Collision tectonics in the Swiss Alps: Insight from geodynamic modeling
Author(s) -
Pfiffner O. A.,
Ellis S.,
Beaumont C.
Publication year - 2000
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/2000tc900019
Subject(s) - geology , subduction , continental crust , crust , nappe , seismology , shear zone , plate tectonics , tectonics , shear (geology) , accretionary wedge , convergent boundary , continental margin , geophysics , petrology , oceanic crust
This paper compares results from two‐dimensional finite element dynamic modeling with the kinematic evolution of the Swiss Alps during the collision phase. In particular, we investigate the role of inherited lateral strength heterogeneities on orogenesis. A number of first‐order characteristics are directly comparable at crustal scales. In the models the entry of continental crust into the convergent margin marks the end of near‐perfect subduction. Accretion of material of the subducting plate to the upper plate creates an orogenic wedge on the incoming (pro)side and initiates a retroshear zone (or model backthrust). The addition of material to the upper plate builds a bivergent orogen. Heterogeneities in the pro‐crust focus shear and lead to the development of “nappe structures” The combined action of pro‐shear (nappe stacking) and retroshear (backthrusting) uplifts a plug between the two shear zones. Subsequent focusing of shear along the retroshear zone results in rotation of the plug and overlying units, leading to crustal‐scale backfolds as observed in the Swiss Alps. The model experiments predict features relevant to Alpine dynamics, including (1) similar crustal thicknesses and exhumation patterns to those observed in the Swiss Alps today for erosion rates comparable to natural ones (1 mm yr −1 ), (2) continued accretion and subduction of upper crustal fragments allowing high‐pressure metamorphic conditions, (3) tilting and exhumation of lower crust when a midcrustal weak zone is present, and (4) “shunting” of material across the strong lower crustal wedge of the upper plate.