Implications of overprinting deformations and fold interference patterns in the Melbourne Zone, Lachlan Fold Belt

Upper crustal shortening associated with development of a northeast‐directed thrust‐belt during dextral strike‐slip ‘docking’ of the Melbourne Zone with the Tabberabbera Zone has led to complex deformation patterns and regional scale fold interference in the Nagambie‐Rushworth area of central Victoria. Mutually interfering, contemporaneous and diachronous north‐south and northeast‐southwest shortening deformations have locally produced ‘dome and basin’ fold patterns due to interference of east‐west and northwest‐southeast fold sets. In the northern part of the zone first generation folds are east‐west‐trending, cut by north‐dipping thrust faults and have a weak, east‐west trending, steeply dipping S, slaty cleavage. To the south, first generation folds are northwest‐southeast trending and show curvilinear axial surface traces and overprinting cleavages in an area of overlapping deformation fronts. The major control is the northeast transport of the Melbourne Zone along a major mid‐crustal detachment whose surface expression is the Mt Wellington Fault Zone. The localised south‐directed thrusting is related to collisional interaction of the Melbourne Zone with the Tabberabbera Zone in the late Early Devonian during dextral strike‐slip convergence of the central/eastern Lachlan Fold Belt with the western Lachlan Fold Belt. Overlapping deformation fronts can be explained by complex movements on underlying detachment faults and the impingement of adjacent blocks during crustal shortening events. Localised, anomalous faults and folds are the result of such block interactions, perhaps due to irregularities in former block margins or to intersections of obliquely intersecting thrust‐systems such as those associated with the Heathcote and Mt Wellington Fault Zones.