A provisional structural thickness map of the Otago Schist, New Zealand

Abstract

Metamorphic zones, terranes and lithologic associations provide a subdivision of the lithologically monotonous Otago Schist on a 10 to 50 kilometer scale. In this study, form line maps of schist foliation have been used to construct a provisional structural thickness map of the Otago Schist that allows a more detailed (1-5 km scale) subdivision of the entire schist. The map shows the macroscopic thickness of schist measured orthogonal to dominant foliation, relative to the datum of the Caples-Rakaia terrane boundary. The structural thickness map provides a new spatial reference frame for the Otago Schist that depicts the differing levels of exhumation of penetratively deformed metamorphic rocks. The structural thickness parameter shows a good correlation with metamorphic grade, white mica grain size, and K-Ar and Ar-Ar ages, thus justifying the simplifying assumptions behind the map's construction. The map reveals several hitherto little-highlighted features including along- and across-strike correlations, interference patterns between Mesozoic and Cenozoic macroscopic folds, net displacement across known and inferred major faults, and relative structural position of mesothermal gold deposits.