Cross-structures in the Lachlan Orogen: The Lachlan Transverse Zone example

The Lachlan Transverse Zone is a major yet subtle west-northwest-trending structure that cuts across the Tasmanides of southeastern Australia. It extends from the western part of the Olepoloko Fault in the west, where it marks the boundary between the Delamerian and Thomson Orogens, across the Lachlan Orogen into the Sydney Basin where it is represented by dykes and intrusions. The western part of the Lachlan Transverse Zone is defined by west-northwest-trending faults. In the Eastern Belt of the Lachlan Orogen, it is defined as a corridor of west-northwest-trending folds and faults that disrupt major folds and faults which constitute the regional grain of the orogen. The Lachlan Transverse Zone was active in the development of the Lachlan Orogen since at least the Middle Ordovician period. It has influenced the partitioning of upper crustal extensional and contractional deformation, the intrusion of igneous bodies as well as the distribution of copper-gold deposits in the Eastern Belt of the orogen. The Lachlan Transverse Zone appears to be an extension of the Proterozoic Amadeus Transverse Zone, as well as an extension of a west-northwest-trending transform segment in the Tasman Line that controlled the Neoproterozoic and Cambrian breakup of cratonic Australia. For these reasons, we suggest that the Lachlan Transverse Zone represents the reactivation of a fundamental crustal weakness in the cratonic lithosphere that propagated into younger Neoproterozoic to Palaeozoic lithosphere of oceanic and continental character.