Macquarie Island - an oceanic fault outdoors .

Macquarie Island , an Australian island located between Tasmania and Antarctica, is one of the few places where you can see with the naked eye an oceanic transform fault, in general completely submerged.

            Macquarie Island - the isthmus connecting Wireless Hill to the island - Photo Hullwarren

The island forms the apex of the MRC - Macquarie ridge complex, a system of ridges and valleys along the boundary of the Australian and Pacific plates , between New Zealand's Alpine fault and the point of triple junction Australia / Pacific / Antarctica.

                          Position of Macquarie island and tectonics  - doc. GeoScienceWorld

The east side of Macquarie exposes subaerial 50 km. of submarine ridges , raised to a height of about 5 km . This unique location allows you to see a sample of oceanic crust, not related to a plume, in subaerial exposure within the basin that formed and processing structures that can be correlated with tectonic known today.

Stretched pillow lava formed on the side of an ancient submarine volcanic edifice are visible on the island.

      Macquarie island -  elongated pillow lava - picture Dr.Nathan Dackzo / Macquarie university

The northern tip of the island , Wireless Hill is attached to Macquarie by a narrow isthmus . Is on the side of the isthmus , we see diabase dykes and on the beach, rocks derived, showing plagioclase phenocrysts typical of the central part of the dyke .
Pebbles of pumice on the west beach arrived there by sea drift, due to a distant eruption.

                          Geological Map of Macquarie Island . gemoc.mq.edu.au
                            Oceanic fault line in bold - fault uprising fine line

Mapping of recent faults affecting the topography of Macquarie show that the island is cut by high- angle normal faults, forming pull-apart basins. (These are lozenge or rhombochasmes basins , where the increase occurred in the direction of stretching. These basins are associated with  sliding faults, creating zones of transtension . )

            Macquarie Island - Sandy Bay - sandy beach and penguins - Photo Antarctica fanpop
  Gorfou de Schlegel - Eudyptes schlegeli - Royal penguin - . Photograph Australian gov / antarctic division

Sandy Bay, less rocky, houses king and royal penguin rookeries, side by side with the elephants of sea. The sparse vegetation cover of the island is threatened by an army of rabbits , which should be eradicated.

Sources:
- Gemoc - Macquarie Island , an exposed oceanic transform fault
- Geological Society of London blog - Macquarie Island
- Australian antarctic division - Macquarie Island