IMPLICATIONS OF OVERPRINTING DEFORMATIONS AND FOLD INTERFERENCE PATTERNS IN THE MELBOURNE ZONE, LACHLAN FOLD BELT

Upper crustal shortening associated with development of a northeast-di rected thrust-belt during dextral strike-slip 'docking' of the Melbour ne Zone with the Tabberabbera Zone has led to complex deformation patt erns and regional scale fold interference in the Nagambie-Rushworth ar ea of central Victoria. Mutually interfering, contemporaneous and diac hronous north-south and northeast-southwest shortening deformations ha ve 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 nort h-dipping thrust faults and have a weak, east-west trending, steeply d ipping S-1 slaty cleavage. To the south, first generation folds are no rthwest-southeast trending and show curvilinear axial surface traces a nd overprinting cleavages in an area of overlapping deformation fronts . The major control is the northeast transport of the Melbourne Zone a long a major mid-crustal detachment whose surface expression is the Mt Wellington Fault Zone. The localised south-directed thrusting is rela ted to collisional interaction of the Melbourne Zone with the Tabberab bera Zone in the late Early Devonian during dextral strike-slip conver gence of the central/eastern Lachlan Fold Belt with the western Lachla n Fold Belt. Overlapping deformation fronts can be explained by comple x movements on underlying detachment faults and the impingement of adj acent blocks during crustal shortening events. Localised, anomalous fa ults and folds are the result of such block interactions, perhaps due to irregularities in former block margins or to intersections of obliq uely intersecting thrust-systems such as those associated with the Hea thcote and Mt Wellington Fault Zones.