Osbourn Trough

The Osbourn Trough, is a 900 km (560 mi)-long extinct mid-ocean ridge, that may have stopped spreading as recently as 79 million years ago. It is a west-to-east oriented sea floor feature, located to the east of the present Tonga-Kermadec Ridge where the present Pacific Plate is under going subduction under a micro-plate of the Australian Plate. The Osbourn Trough is key to understanding the postulated breakup mechanism of the historic massive Ontong Java-Manihiki-Hikurangi large igneous province (LIP), as it has been shown to be the spreading centre that lead to the separation of the Manihiki Plateau to its north and the Hikurangi Plateau to its south close to New Zealand.

The major geological relationships of the Osbourn Trough. It defines with the Louisville Ridge intersection the Tonga Trench (violet) to the north and the Kermadec Trench (violet) to the south. Blue represents ocean depths of a kilometer or so and brown shades are shallower. Land is shown in dark green. The black line delineates the continent of Zealandia.
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