Structural history of the Arthur Lineament, northwest Tasmania: an analysis of critical outcrops

Abstract

The Arthur Lineament of northwestern Tasmania is a Cambrian (510 10 Ma) high-strain metamorphic belt. In the south it is composed of metasedimentary and mafic meta-igneous lithologies of the 'eastern' Ahrberg Group, Bowry Formation and a high-strain part of the Oonah Formation. Regionally, the lineament separates the Rocky Cape Group correlates and 'western' Ahrberg Group to its west from the relatively low-strain parts of the Oonah Formation, and the correlated Burnie Formation, to its east. Early folding and thrusting caused emplacement of the allochthonous Bowry Formation, which is interpreted to occur as a fault-bound slice, towards the eastern margin of the parautochthonous 'eastern' Ahrberg Group metasediments. The early stages of formation of the Arthur Lineament involved two folding events. The first deformation (CaD1) produced a schistose axial-planar fabric and isoclinal folds synchronous with thrusting. The second deformation (CaD2) produced a coarser schistosity and tight to isoclinal folds. South-plunging, north-south stretching lineations, top to the south shear sense indicators, and south-verging, downward-facing folds in the Arthur Lineament suggest south-directed transport. CaF1 and CaF2 were rotated to a north-south trend in zones of high strain during the CaD2 event. CaD3, later in the Cambrian, folded the earlier foliations in the Arthur Lineament and produced west-dipping steep thrusts, creating the linear expression of the structure.