The Narooma terrane is a distinct geological structural unit located within the eastern subprovince of the Lachlan Orogen in New South Wales, Australia. It is situated along the state's south coast, with prominent exposures occurring in the vicinity of the town of Narooma.
Geologically, the Narooma terrane is characterized as an accretionary complex consisting of oceanic rock sequences that were incorporated into the Australian continental margin during the Paleozoic era. The unit is primarily composed of the Narooma Chert, which includes a succession of radiolarian cherts, mudstones, and turbidites ranging in age from the Cambrian to the Late Ordovician or Early Silurian. Additionally, the terrane contains remnants of oceanic crust, such as pillow basalts and volcaniclastics, which indicate a deep-marine origin.
The significance of the Narooma terrane lies in its tectonic history. It is interpreted by geologists as a far-travelled slice of the paleo-Pacific ocean floor that was scraped off a subducting plate and accreted onto the margin of the Gondwana supercontinent. This process resulted in intense deformation, characterized by complex folding, thrust faulting, and the development of melange zones where different rock types are tectonically mixed.
The boundary between the Narooma terrane and the adjacent turbidite-dominated sequences of the Lachlan Fold Belt is marked by major fault systems. Its presence provides critical evidence for the long-lived subduction-accretion processes that shaped the eastern edge of the Australian continent throughout the Early Paleozoic.