thrusts have been proposed by Brandon and Ring of the Helvetic nappes. We regard this option as (1998), who summarized five quantitative studies of unrealistic because of the regionally low strains and ductile deformation from deeply exhumed he lack of evidence for pronounced non-coaxial accretionary wedges. They concluded that flow there deformation in large parts of the Verrucano. We is almost always coaxial because the subduction thrust propose that the flat-lying foliation in the verrucano is was too weak transmit a significant shear tractio basically a result of pronounced vertical shortening These findings bring up the question of how intra that accompanied nappe translation. This would imply nappe deformation relates to nappe translation in that early Calanda-phase nappe stacking in the Glarus orogens. In general, there are two different ideas in Alps was not by simple shear. It also implies that the thrust belts. The first is that ductile strain in nappes is exhumation of the Glarus thrust was not solely due to distinctly non-coaxial with stretching lineations erosion but has also been aided by coaxial vertical parallel to thrust transport at the base of the nappes. A shortening. Assuming an initial depth of 12-15 km and certain amount of coupling at faults is needed to a residence time within the ductile crust of about 25 internally shear adjacent thrust nappes. In the western Myr, we calculate, using the one-dimensional Helvetic nappes for example, Ramsay and Huber numerical model of Feehan and Brandon(1999), that (1983)showed that carbonates of the Morcles nappe vertical ductile shortening contributed about 1.5 km supply strong evidence for shear. Studies in the (at rates of 0. 2 km/Myr) to the exhumation of the strongly ductilely deformed Penninic nappes also Glarus thrust. i. e. about 10% appear to support such a view(e.g. Merle et al., 1989; Ring, 1992). The second idea is that faults are weak Acknowledgements as suggested for the Lochseitenkalk at the glarus This study was funded by the deutsche thrust(Hsu, 1969, Schmid, 1975). The two different Forschungsgemeinschaft through the concepts may, at least in part, depend on the strengt Graduiertenkolleg" Stoffbestand von Kruste und contrast between the mylonite between nappes and the Mantel at Mainz University and a us/German interior of the nappe. The viscosities of the carbonates exchange program funded by the National Science of the Morcles nappe and the Lochseitenkalk are Foundation and the deutscher Akademischer different. In the Morcles nappe, limestones are Austauschdienst. We thank meinert rahn bas den deformed by dislocation creep(ramsay and Huber Brok and Oliver Jagoutz for numerous discussions and 1983). For the Lochseiten mylonite, Schmid (1982) Stefan Schmid and Kyuichi Kanagawa for careful proposed deformation by superplastic flow. We have reviews and Richard Lisle for editorial handling shown that deformation in the Glarus nappe and the North Helvetic flysch is approximately coaxial, as expected for a weak thrust. Therefore, the Lochseitenkalk was probably considerably weaker than the limestone in the Morcles nappe and this rheologic contrast might have controlled the different structural styles in the Helvetic nappes of western and eastern switzerland caused vertical thinning of the overlying wedge a g) We propose that deep accretion(ie. underpl recorded by the formation of a subhorizontal clear in the hanging wall of the glarus thrust. Vertical shortening of 30% appears to be balanced by mass loss Our rotation data show that the foliation formed during a weakly non-coaxial deformation within large parts of the Glarus nappe. In a typical foreland fold- and-thrust belt, one would expect the foliation in a thrust sheet to be at a high angle to the underlying thrust and then curving asymptotically into subparallelism with the thrust plane theoretically the flat-lying foliation in the Verrucano could be due to rotation as a result of large non-coaxial strains, i.e. that the Verrucano represents a huge shear zone at the base10 thrusts have been proposed by Brandon and Ring (1998), who summarized five quantitative studies of ductile deformation from deeply exhumed accretionary wedges. They concluded that flow there is almost always coaxial because the subduction thrust was too weak transmit a significant shear traction. These findings bring up the question of how intra￾nappe deformation relates to nappe translation in orogens. In general, there are two different ideas in thrust belts. The first is that ductile strain in nappes is distinctly non-coaxial with stretching lineations parallel to thrust transport at the base of the nappes. A certain amount of coupling at faults is needed to internally shear adjacent thrust nappes. In the western Helvetic nappes for example, Ramsay and Huber (1983) showed that carbonates of the Morcles nappe supply strong evidence for shear. Studies in the strongly ductilely deformed Penninic nappes also appear to support such a view (e.g. Merle et al., 1989; Ring, 1992). The second idea is that faults are weak, as suggested for the Lochseitenkalk at the Glarus thrust (Hsü, 1969; Schmid, 1975). The two different concepts may, at least in part, depend on the strength contrast between the mylonite between nappes and the interior of the nappe. The viscosities of the carbonates of the Morcles nappe and the Lochseitenkalk are different. In the Morcles nappe, limestones are deformed by dislocation creep (Ramsay and Huber, 1983). For the Lochseiten mylonite, Schmid (1982) proposed deformation by superplastic flow. We have shown that deformation in the Glarus nappe and the North Helvetic flysch is approximately coaxial, as expected for a weak thrust. Therefore, the Lochseitenkalk was probably considerably weaker than the limestone in the Morcles nappe and this rheologic contrast might have controlled the different structural styles in the Helvetic nappes of western and eastern Switzerland. We propose that deep accretion (i.e. underplating) caused vertical thinning of the overlying wedge, as recorded by the formation of a subhorizontal cleavage in the hanging wall of the Glarus thrust. Vertical shortening of 30% appears to be balanced by mass loss. Our rotation data show that the foliation formed during a weakly non-coaxial deformation within large parts of the Glarus nappe. In a typical foreland fold￾and-thrust belt, one would expect the foliation in a thrust sheet to be at a high angle to the underlying thrust and then curving asymptotically into subparallelism with the thrust plane. Theoretically the flat-lying foliation in the Verrucano could be due to rotation as a result of large non-coaxial strains, i.e. that the Verrucano represents a huge shear zone at the base of the Helvetic nappes. We regard this option as unrealistic because of the regionally low strains and the lack of evidence for pronounced non-coaxial deformation in large parts of the Verrucano. We propose that the flat-lying foliation in the Verrucano is basically a result of pronounced vertical shortening that accompanied nappe translation. This would imply that early Calanda-phase nappe stacking in the Glarus Alps was not by simple shear. It also implies that the exhumation of the Glarus thrust was not solely due to erosion but has also been aided by coaxial vertical shortening. Assuming an initial depth of 12-15 km and a residence time within the ductile crust of about 25 Myr, we calculate, using the one-dimensional numerical model of Feehan and Brandon (1999), that vertical ductile shortening contributed about 1.5 km (at rates of 0.2 km/Myr) to the exhumation of the Glarus thrust, i.e. about 10%. Acknowledgements This study was funded by the Deutsche Forschungsgemeinschaft through the Graduiertenkolleg “Stoffbestand von Kruste und Mantel” at Mainz University and a US/German exchange program funded by the National Science Foundation and the Deutscher Akademischer Austauschdienst. We thank Meinert Rahn, Bas den Brok and Oliver Jagoutz for numerous discussions and Stefan Schmid and Kyuichi Kanagawa for careful reviews and Richard Lisle for editorial handling