Basaltic dykes and their xenoliths from the Gerroa–Kiama region, southern Sydney Basin, New South Wales: evidence for multiple intrusive episodes

The orientation, petrography and geochemistry of numerous basaltic dykes between Kiama Gerroa were investigated in this study. Geochemical analysis shows that the range from sub-alkaline to alkaline composition. fit into three distinct geochemical groups, with most being transitional alkali basalts foidites, followed by lastly andesites/basaltic andesites. We suggest intrusive episodes occurred based on petrographic classification. contain phenocrysts olivine, plagioclase clinopyroxene a fine-grained groundmass. Multiple microtextures found, including porphyritic, glomeroporphyritic, amygdaloidal, aphanitic intergranular. Most strike northwest–southeast, two east–west, four northeast–southwest. One dyke south Boat Harbour Reserve contains xenoliths, gabbroic, granitic charnockitic types. gabbroic xenoliths likely sourced mid-crust, whereas derived upper crust. Joints study area north–south, east–west dominant joint set strikes secondary sets least pervasive approximately north–south. intruded along long-lived inherent structural weaknesses host rocks, as their orientations match sets. Geochemically, are having an abundance which rare within Sydney Basin. They clearly different nearby Permian K-rich Gerringong Volcanics, but many like those Basin, foidites similar composition lower Eocene Kulnura basalt NSW Central Coast. geographic distribution strongly magmas have been injected through same upper-crustal over protracted period. KEY POINTSDykes occurring fall under separate groups: andesites.Three classification.The rocks.