Origin, structural and tectonic history of the Macquarie Island region

Macquarie Island, in the Southern Ocean, was formed by oceanic crust uplift due to transpressive forces between the Indian / Australian and Pacific oceanic plates, in a transpressional regime which has persisted over the last 10 Ma. The amount of uplift is affected by regional isostatic compensation for crustal thickening; accompanying effects are tilting of rocks and rotation of the southern segment of the island. Gabbro and serpentinite, in the north, and basalts, in the south, all of which were formed in the primary oceanic crust, are now exposed. Consequently, magnetic properties of igneous rocks on the island correlate with similar features on the Indian plate which is on both sides of it. In conflict with evidence from younger palaeontological and potassium-argon (K-Ar) dating, which may reflect later episodes, this suggests that the original oceanic crust composing the island was formed at the Indian-Antarctic accreting mid-oceanic ridge around the time of anomaly 7 (27 Ma BY.)