Abstract

Lothar Ratschbacher writes: I would like to discuss three questions raised by Fry (1989a) concerning the kinematic evolution of the Alpine arc on the basis of recent structural data from the Eastern Alps.

(i) Is there a continuous sweep in the direction of orogenic displacements around the Alpine arc (the ‘radial outward’ hypothesis)? Overall motion directions of nappes in the Eastern Alps have been derived mainly from the analysis of Mesozoic facies troughs. Because these troughs were assumed to strike E–W (but see Weissert & Bernoulli 1985) and because they are partly superposed today, a top to the north motion was derived (e.g. Tollmann 1987). For a kinematic structural analysis of intraplate displacements, Choukroune et al. (1986) showed the necessity to split the total displacement pattern into a time sequence. In Fig. 1 displacements in the Eastern Alps are factorized into stages of orogenic wedge evolution: stacking-imbrication, unroofing and tectonic escape (for use of the term 'tectonic escape' see Burke & Sengör 1986; Ratschbacher et al. 1989). Displacement directions are generally orientated E-W, subparallel to the strike of the orogen, regardless of their mode of formation. These data invalidate the radial outward hypothesis for motions in the Eastern Alps and stress the importance of detailed kinematic structural analysis.

(ii) Do stretching and displacement lineations in an intraplate region reflect plate motions? We (Ring et al. 1988) assumed the following in the work in the Eastern Alps: stretching and displacement lineations reflect plate motions if acquired during the stage when a

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