Deformational History and Shape Analysis of Folds in the Metamorphic Rocks of the Petermann Ranges, East Antarctica

Abstract

Considered earlier to be very little defonned, the granulite facies rocks of the Petennann Ranges, East Antarctica, reveal three phases of folding and two episodes of ductile shearing. These metamorphic rocks preserve the F₁ folds as small scale, rootless, intrafolial features with tight to isoclinal profiles, and F₂ folds as mesoscopic features with close to tight profiles. F₁ and F₂ folds are coaxial and broadly coplanar having axial surfaces marked by pervasive NW-SE striking foliation. F₃ folds are open, upright with N-S to NNW-SSE axial planes and impart local swings in the regional foliation. The early ductile shears produce a strong mylonitic fabric and are synchronous to F₁, while occurring as thin wavy zones, the later shears are post F₂.

Shape and geometric analyses of representative folds show that F₁ folds belong to class 2 and 1C at low and high limb dips respectively and are fonned dominantly by flexural flow. F₂ folds exhibit geometric features of class 1C at low as well as high limb dips and owe their origin to buckling with a flexural slip component and flattening.