Statistical Analysis of Directional Features - Geomathematics: Theoretical Foundations, Applications and Future Developments - page 298

results presented in this section (Figs. 8.12 , 8.13 , 8.14 and 8.15 ), this movement
probably had a horizontal component as well, as indicated by the subvertical to
steeply SSW dipping B-axes In the vicinity of Bruneck and immediately south of
the Permian granodiorite intrusion. The shortening probably also involved north
vergent thrust faults including the Villn ¨ sz Fault south of Brixen. Although it is
difficult to estimate the amount of shortening precisely, Castellarin et al.'s estimate
is in agreement with the pattern shown in Fig. 8.12 , and also with the model of
pronounced neo-Alpine shortening in the Pustertal area further eastward. (Fig. 8.18 )
The main reason that significant extra eastward shortening took place in the
Pustertal is probably related to the decrease in width of the quartzphyllite belt in
this direction. Agterberg ( 1961 ) estimated that the later Pustertal shortening was
about 5 km. In his original model, amount of shortening was assumed to decrease
with depth. This assumption was probably not correct because extra neo-Alpine
shortening in Pustertal was probably between 10 and 15 km. The Hercynian s -
planes were reactivated during these strong upward movements. Although there is
some evidence of existence of neo-Alpine micro-structures in the area (Agterberg
1961 , Appendix I, Figs. 48-51a), the topic of distinguishing between Hercynian and
Alpine micro-structures would benefit from further study using methods similar to
those applied to microstructures in the Austroalpine units and within the Tauern
Window north of the Periadriatic Lineament (Mancktelow et al. 2001 ).
8.2.6 Summary of Late Alpine Tectonics South
of Periadriatic Lineament
The purpose of this section was to revisit the topic of unit vector field fitting in
applications to B-axes in the quartzphyllites of the crystalline basement of the
Italian Dolomites. A slightly improved mathematical derivation of the use of
polynomial trend functions fitted to the three direction cosines of directional
features and combining the results was presented. Illustration by practical applica-
tions consisted of three parts. First it was shown that in the San Stefano area, to the
east of the Dolomites, the relatively simple method of computing vector means for
relatively large, overlapping circular areas produces good results. This would imply
that neighbourhood-based methods as proposed by Watson ( 1971 ) can give good
results. During Alpine orogeny the San Stefano quartzphyllites formed the core of a
SSW vergent anticline with re-activation of steeply dipping Hercynian schistosity
causing opposite rotations of the originally sub-horizontal Hercynian B-axes at the
two sides of its axial plane.
Secondly, the polynomial unit vector fitting method was illustrated by means of
a relatively simple, linear example. Data from six measurement samples along the
Gaderbach south of Bruneck in the Pustertal were projected on a north-south line
approximately coinciding with the TRANSALP profile. The quartzphyllite belt is
about 12 km wide at this location. Immediately north of the Permotriassic of the