⁴⁰Ar/³⁹Ar mineral age constraints on the Paleozoic tectonothermal evolution of high-grade basement rocks within the Ross Orogen, central Transantarctic Mountains

⁴⁰Ar/³⁹Ar ages were determined for hornblende and muscovite from several lithotectonic subunits of the Nimrod Group exposed in the Miller Range, including amphibolitic gneiss, ca. 1.7 Ga orthogneiss, and metasedimentary mica schist. These rocks display ductile deformation fabrics that formed prior to intrusion of ca. 500 Ma, post-kinematic granitic plutons. The ⁴⁰Ar/³⁹Ar data indicate that conventional K-Ar dates (up to 1100 Ma) previously reported for hornblende from the Miller Range probably have no geologic significance because of the widespread presence of extraneous argon. They cannot, therefore, be regarded as dating any "pre-Ross' event(s) . -from Authors