Tectonic Relationship between the Late Ordovician and Late Silurian palaeogeographies of southeastern Australia

The Ordovician palaeogeography of southeastern Australia was an east‐facing mafic volcanic island arc separated from the Gondwanan continent by a marginal sea, probably floored by oceanic crust. By mid‐Silurian the palaeogeography had changed to an almost wholly ensialic configuration, with meridional horsts and grabens east of the Wagga Metamorphic Belt and widespread silicic magmatism. By extending a previously postulated match between the modern Andaman Basin and parts of southeastern Australia in the Late Ordovician, the transition from the Late Ordovician to Late Silurian palaeogeography can be explained. The entire Ordovician and Silurian interval can be understood in terms of a relatively simple and constant plate geometry involving southeastern Australia in regional dextral shear.