Before the orogeny the rocks of the coastal area were formed. During Late Carboniferous there was a continental margin with an oceanic trench subducting the ocean floor off the coast. To the east there was a magmatic arc. This includes Connors Arch, Auburn Arch, Combarrago Volcanics and the Bathurst Batholith. A forearc basin in between included the Tamworth Belt and Yarrol Belt. Subduction resulted in blueschist metamorphism. At 309 Ma a mid oceanic ridge plate boundary encountered the subduction boundary near Tin Can Bay south of Fraser Island on the North D'Aguilar block. Another encounter point was near what is now Coffs Harbour. These ridge encounters with the trench stopped the subduction at those points and resulted in triple junctions moving north and south up the trench, and being replaced by a dextral transform fault.