At a
regional scale, the Otago Schist has been divided into textural zones,
metamorphic zones, structural transposition zones, and terranes and lithologic
associations. Each of these subdivisions reveals aspects of the internal
structure of the lithologically monotonous Otago Schist but, to date, a map of
the schist derived directly from structural data has not been made. In the
present study, digitised structural data from the QMAP GIS were used to make a
form line map of Schist foliation which, in turn (and using certain non-unique
guiding assumptions), was used to construct a provisional foliation thickness
map of the Otago Schist. Contours of dominant foliation (Sp) thickness have been
drawn from 4 kIn above to 16 km below the reference level of the Caples-Torlesse
terrane boundary in the schist structural pile. A recent revision of the Otago
Schist textural zone classification has shown that the grain size of metamorphic
white micas increases progressively with textural
grade. There also
appears to be a correlation between schist mica grain size and foliation
thickness. Using mica grain size, it may eventually be feasible to establish the
vertical structural position of samples in greenschist facies parts of the
schist pile to a precision of 1 km or better, even if they are in inliers or
fault-bounded blocks. Foliation thickness and mica grain size are thus
potentially useful tools for research and exploration in the Otago Schist in
that they assist with structural interpolation and extrapolation. Even at this
early stage of application they can be used to provide hitherto unobtainable,
semi-quantitative estimates of displacement on Mesozoic and Cenozoic faults and
folds.