South Arunta Block: the internal zones of a Proterozoic overthrust in central Australia

Abstract

A detailed structural and microstructural analysis indicates that the Chewings Range area (south Arunta Block) was deformed during a north-directed shearing event. The Chewings Range quartzite and metasediments together with their granitic basement were involved in a Proterozoic ductile deformation event responsible for a flat-lying foliation axial planar to N-S trending isoclinal folds. Within the foliation, a N-S oriented lineation developed parallel to a plane strain shearing or constrictive stretching direction in all rock types. A ductile stretching of 100–150% was achieved during this strain history. Shear criteria observed in the gneisses are consistent with the asymmetric pattern of quartz c-axis fabrics in the quartzite and indicate a south over north shear component. Strain is concentrated in narrow high-strain zones which delineate a stack of complexly folded thrust sheets. These results provide a new interpretation for the Early to Middle Proterozoic of central Australia. The south Arunta Block may represent the internal zones of a north-directed Proterozoic overthrust. Correlation between structural elements of the south Arunta Block and the granulite belt to the north is unclear. Until this problem is resolved by careful dating it is suggested that D 2 did not develop in the granulitic rocks owing to an intracrustal detachment above them.