Macquarie Island mapping reveals three tectonic phases



The first detailed mapping of Macquarie Island, perhaps the world's quintessential ophiolite has revealed three tectonic phases—extension, transtension, and transpression. Nearly all of the crust and most deformational structures formed during the first phase (D1), which involved extension along the paleo-Macquarie seafloor spreading axis. Magmatism, block tilting, and large-scale differential block uplift were synchronous, resulting in juxtaposition of disparate rock associations characteristic of different crustal levels. As D1 waned, the second phase (D2) developed. Involving transtension with a north-south extension axis, it produced minor late-stage dolerite dikes and seafloor volcanic centers.The third phase (D3), still in progresses dextral transpression. Its initiation along the Australia-Pacific plate boundary terminated igneous activity and extension on the island.The D3 shortening axis trends east-west to northeast-southwest.