In addition to the remarks of Rob Twiss:
When we studied nappe stacking in relation to subduction in the Aegean
region, we came to a scenario quite comparable to Pfiffner's. We
haven't studied the internal structure of the nappes in this paper,
but it may be of relevance to this interesting discussion that Maarten
kick-started:
van Hinsbergen, D.J.J., Hafkenscheid, E., Spakman, W., Meulenkamp,
J.E., and Wortel, M.J.R., 2005, Nappe stacking resulting from
subduction of oceanic and continental lithosphere below Greece:
Geology v. 33 (4), p. 325-328. (see www.geologist.nl for pdf)
Cheers
Douwe
--
http://www.geologist.nl
Dr. Douwe J.J. van Hinsbergen
Geological Survey of Norway, NGU
Center of Geodynamics
Leiv Eirikssons vei 39
7491 Trondheim
+47 73904273
Norway
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On Tue, Mar 3, 2009 at 11:16 PM, <[log in to unmask]> wrote:
>
> As to the emplacement mechanism of nappes, an eye-opening (for me) paper
> that I recommend to anyone trying to understand this process is
>
> Pfiffner, O.A., S.Ellis, and C.Beaumont. 2000. Collision tectonics in the
> Swiss Alps: Insight from geodynamic modeling. Tectonics 19(6): 1065-1094.
>
> The model for the emplacement of the Alpine nappes is that they originate
> within the subduction zone as long imbricated slices off the down-going
> Eurpoean foreland, and that they get stacked up in the orogen and uplifted
> through a combination of underplating of the nappe slices and erosion off
> the top. The numerical model, while is cannot reproduce the details of
> this process, shows quite clearly how material gets sheared off the
> down-going plate and piled up in, and uplifted through the orogen. It
> even gives suggestions of how large fold nappes could develop, although
> again, the model is coarser in scale than the details that we can now
> observe of the uplifted nappes. Thus the major displacement at the base
> of the nappes occurs at the subduction interface, although subsequent
> deformation occurs within the orogenic pile during uplift due to
> underplating of new nappes, and presumably due to some extent to
> gravitational collapse of the orogenic pile.
>
> Such a sequence can account for either thrust or fold nappes, presumably
> depending on the rheology of the material when it is transferred from the
> down-going to the over-riding plate; it can account for the large extent
> of nappes both parallel and perpendicular to the shear direction; it can
> account for the large displacements at the base of the nappes; and it can
> account for subsequent deformation of the nappes that has been mentioned
> by several contributors to this discussion.
>
> I think this is a very insightful paper and highly recommend it if readers
> have not already seen it.
>
> Dr. Pfiffner was kind enough to let us reproduce a couple of figures from
> that paper in the 2nd edition of our Structural Geology text (Twiss &
> Moores, 2007, W.H.Freeman & Co; Figures 20.20 A&B, 20.34).
>
> Cheers,
>
> rob twiss
--
http://www.geologist.nl
Dr. Douwe J.J. van Hinsbergen
Geological Survey of Norway, NGU
Center of Geodynamics
Leiv Eirikssons vei 39
7491 Trondheim
+47 73904273
Norway
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