The Green Scrub Basalt and its association with the Lapstone Structural Complex, eastern New South Wales

The Green Scrub Basalt is located on the western side of the Lapstone Structural Complex (LSC) in the Sydney Basin. It was initially mapped as a neck, but more recently it has been viewed as a flow associated with other basalts in the Blue Mountains Volcanic Province. As a consequence, it was inferred that the age of the LSC was at least the age of the basalt, dated at 18.8 Ma. This study has carefully mapped the Green Scrub Basalt and re-establishes it as a neck. As such it does not constrain the age of the LSC. Local dips across the LSC show that the structure of the LSC is likely to be a fault propagation fold above a west-dipping thrust. The structure may have been initiated in the Neogene when pollens were deposited at nearby Mountain Lagoon. The Lapstone Structural Complex is a 100 km-long association of structures in the Sydney Basin now thought to have formed in the late Cenozoic. The Green Scrub Basalt, south of Mountain Lagoon, dated at 18.8 Ma is a volcanic neck and thus provides no constraint on the age of the Lapstone Structural Complex. Previously the Green Scrub Basalt was considered a flow, but we confirm that earlier geologists were correct in their assessment of the basalt as a volcanic neck.