The boundary relationship of the Concert Schist and the Oonah Quartzite and Slate correlate at Dundas

Abstract

The boundary between the metasedimentary Concert Schist (Precambrian) and the adjacent correlate of the relatively unmetamorphosed Oonah Quartzite and Slate (also Precambrian) at the western edge of the Concert Schist near its type section on Concert Creek near Dundas, Tasmania, is regarded as marking a sharp transition in degree of deformation and metamorphism. Three cleavages, mineral segregation and quartz recrystallisation were found in the Concert Schist whereas two cleavages and only minor mineral segregation and quartz recrystallisation were found in the Oonah Formation correlate. Quartz optic axes fabrics obtained from psammites in the Concert Schist and Oonah Quartzite and Slate correlate are similar and show relatively weak preferred orientation. These fabrics and fabrics recorded earlier demonstrate that Precambrian strata in Tasmania which are classed as metamorphosed cannot in all cases be distinguished from those that are classed as relatively unmetamorphosed on the basis of quartz optic axes fabrics present in psammites.