Abstract
The different upper- and lower-plate settings of detachment-related geometries of passive margins controlled by different extensional geometries can strongly influence the geodynamics and resultant vergence of subsequent active convergent margins during contractional orogenic development. The observed vergence along the Tasman Line and also the foreland-directed vergence of the early Tasmanides (Kanmantoo Fold Belt) and the miogeoclinal belt (Adelaide Fold Belt) support this concept. The less frequently recognized mixed vergence, like that in the Lachlan Fold Belt, has probably been caused by microcontinents and tectonically underplated terrane(s) which acted as structural backstops during the prolonged and complicated orogenic contraction. The geometry of the orogenic float (the mechanically separated surficial rock complexes and crustal units from the underlying continental and oceanic lithosphere) was strongly influenced by the relative displacement of several individual basement domains (some microcontinents) separated by long-lived, (i.e. reactivated), sutures and/or root zones.
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