during the deformation, whereas the cleavage using the Hencky method where only the stretch approximates the XY plane of the finite deformation tensor is needed(see Appendix B of Brandon, 1995) Internal rotation was estimated using the FIBer program to model the shape of about 30-50 fibres 3.3. Results The internal rotation axis is assumed to parallel o digitised in the XZ section(Ring and Brandon, 1999) bles i and 2 list our deformation measurements for the Verrucano and melser sandstones from the Tables I and 2 report internal rotation and average Helvetic nappes above the glarus thrust, and for the kinematic numbers for Smt deformation Internal Taveyannaz and north helvetic flysch sandstones rotation is represented by a right-handed rotation axis from the Infrahelvetic complex below the thrust defined by a trend and plunge, and a rotation angle, Sample locations are shown in Fig. 2. Note that most Q2j. Wn and Wm are the average kinematic vorticity of our samples from the Helvetic nappes an e trom numbers and Am the average kinematic dilatancy more than 1 km above the thrust plane The stereograms(Fig. 5)show that the z directions number(Means et al., 1980; Passchier, 1991; Means are clustered around a steeply plunging maximum, and 1994; Ring and Brandon, 1999). Definitions and other the X and y directions are scattered in a weakly details are given in Ring and Brandon(1999). A brief defined subhorizontal girdle. The average for Z(Table review is provided here. The m subscript for the 2)defines the average flattening plane, which has a kinematic numbers indicates a path-averaged value strike of 30 and a dip of 10 to the SE. The average X assuming a steady three-dimensional deformation. If direction is close to horizontal, although its trend SMt deformation were unsteady, then Wm would changes from 200 above the glarus thrust to 160% have no direct relationship to the time history of the below the thrust. The Nadai plot(Fig. 6)shows a instantaneous kinematic vorticity number Wk. The scatter of both prolate and oblate strain symmetries simple geometry of the overgrowths in our samples The strain type(Fig. 7)is generally weakly suggests that Smt deformation was fairly steady, at constrictional, as indicated by S, <1 (Table 1). The principal stretches indicate that the constrictional least in its orientation. An asterisk indicates that the aspect of the strain is primarily the result of shortening kinematic number is based on the deviatoric stretching in the y and Z directions and not extension in X rate rather than the absolute stretching rate. Thus, a Above the glarus thrust. local measurements from coaxial deformation is indicated by =0 and a non- the Verrucano and melser sandstones have X strains coaxial simple-shear deformation by Wm=l ranging from +5 to +43%and Z strains, from to regardless of the amount of volume strain. A 52%. The tensor average indicates absolute principal stretches of 1. 07.0.89 and 068. Thus at the regional describes the average ratio of the volume -strain rate lative to the deviatoric stretching rate(Passche scale, SMT deformation was constrictional (1>S 1991; Ring and Brandon, 1999). The deformation is S,)and approximately plane strain(Sr= 1). This isochoric if A=0. dilatant if A>0 and surprising result, with S, =1, stems from the variable orientations of X and y in the flattening plane, which compactive if Am <0. For example, a deformation means that local extensional strains are averaged out at involving uniaxial shortening and an equal loss of the regional scale volume, would have A=-l because the rates of Below the Glarus thrust, individual samples show haller strain magnitudes in X and y. For instance. X olume strain and deviatoric strain would be equal but strains range from +3 to +12%. In contrast, the tensor opposite in sign average indicates absolute principal stretches of 0.99 Table 2 reports tensor averages for our deformation 0.88 and 0.73, which is nearly identical to the tensor measurements As discussed in Brandon(1995) average above the thrust Thus the low strain deformation data must be averaged in tensor form to magnitudes in X and y are only manifested at the local ensure that the magnitudes and directions of the cale. At the regional scale, sandstones above and I stretches and rotations are correctly below the fault record a similar smt deformation associated. If the rotational component of the deformation is small. then one can average the stretch involving constrictional plane strain The absolute strain data indicate pronounced mass- tensor and the internal rotation tensor separately, without introducing significant errors(Brandon, loss volume strains ranging from-9 to-54% in the 1995). In this study, tensor averages were calculated sandstones above the glarus thrust. and -8 to -49% for sandstones below the thrust. The average is the same for both 36%. At the outcrop7 during the deformation, whereas the cleavage approximates the XY plane of the finite deformation. Internal rotation was estimated using the FIBER program to model the shape of about 30-50 fibres digitised in the XZ section (Ring and Brandon, 1999). The internal rotation axis is assumed to parallel Y. Tables 1 and 2 report internal rotation and average kinematic numbers for SMT deformation. Internal rotation is represented by a right-handed rotation axis, defined by a trend and plunge, and a rotation angle, Ωi. Wm and * Wm are the average kinematic vorticity numbers and * Am the average kinematic dilatancy number (Means et al., 1980; Passchier, 1991; Means, 1994; Ring and Brandon, 1999). Definitions and other details are given in Ring and Brandon (1999). A brief review is provided here. The m subscript for the kinematic numbers indicates a path-averaged value assuming a steady three-dimensional deformation. If SMT deformation were unsteady, then * Wm would have no direct relationship to the time history of the instantaneous kinematic vorticity number * Wk . The simple geometry of the overgrowths in our samples suggests that SMT deformation was fairly steady, at least in its orientation. An asterisk indicates that the kinematic number is based on the deviatoric stretching rate rather than the absolute stretching rate. Thus, a coaxial deformation is indicated by * Wm = 0 and a non￾coaxial simple-shear deformation by * Wm = 1, regardless of the amount of volume strain. * Am describes the average ratio of the volume-strain rate relative to the deviatoric stretching rate (Passchier, 1991; Ring and Brandon, 1999). The deformation is isochoric if * Am = 0, dilatant if * Am > 0, and compactive if * Am < 0. For example, a deformation involving uniaxial shortening and an equal loss of volume, would have * Am = –1 because the rates of volume strain and deviatoric strain would be equal but opposite in sign. Table 2 reports tensor averages for our deformation measurements. As discussed in Brandon (1995), deformation data must be averaged in tensor form to ensure that the magnitudes and directions of the principal stretches and rotations are correctly associated. If the rotational component of the deformation is small, then one can average the stretch tensor and the internal rotation tensor separately, without introducing significant errors (Brandon, 1995). In this study, tensor averages were calculated using the Hencky method where only the stretch tensor is needed (see Appendix B of Brandon, 1995). 3.3. Results Tables 1 and 2 list our deformation measurements for the Verrucano and Melser sandstones from the Helvetic nappes above the Glarus thrust, and for the Taveyannaz and North Helvetic flysch sandstones from the Infrahelvetic complex below the thrust. Sample locations are shown in Fig. 2. Note that most of our samples from the Helvetic nappes are from more than 1 km above the thrust plane. The stereograms (Fig. 5) show that the Z directions are clustered around a steeply plunging maximum, and the X and Y directions are scattered in a weakly defined subhorizontal girdle. The average for Z (Table 2) defines the average flattening plane, which has a strike of 30° and a dip of 10° to the SE. The average X direction is close to horizontal, although its trend changes from 200° above the Glarus thrust to 160° below the thrust. The Nadai plot (Fig. 6) shows a scatter of both prolate and oblate strain symmetries. The strain type (Fig. 7) is generally weakly constrictional, as indicated by SY < 1 (Table 1). The principal stretches indicate that the constrictional aspect of the strain is primarily the result of shortening in the Y and Z directions, and not extension in X. Above the Glarus thrust, local measurements from the Verrucano and Melser sandstones have X strains ranging from +5 to +43% and Z strains, from −22 to −52%. The tensor average indicates absolute principal stretches of 1.07, 0.89 and 0.68. Thus, at the regional scale, SMT deformation was constrictional (1 > SY > SZ) and approximately plane strain (SX ≈ 1). This surprising result, with SX ≈ 1, stems from the variable orientations of X and Y in the flattening plane, which means that local extensional strains are averaged out at the regional scale. Below the Glarus thrust, individual samples show smaller strain magnitudes in X and Y. For instance, X strains range from +3 to +12%. In contrast, the tensor average indicates absolute principal stretches of 0.99, 0.88 and 0.73, which is nearly identical to the tensor average above the thrust. Thus, the low strain magnitudes in X and Y are only manifested at the local scale. At the regional scale, sandstones above and below the fault record a similar SMT deformation involving constrictional plane strain. The absolute strain data indicate pronounced mass￾loss volume strains ranging from −9 to −54% in the sandstones above the Glarus thrust, and −8 to −49% for sandstones below the thrust. The average is the same for both groups, −36%. At the outcrop scale