Vityaz Trench

The Vityaz Trench (also known as the Vitiaz or East Melanesian Trench ) is an oceanic trench tectonic feature of the South West Pacific Ocean floor.

History
It is named after the Russian research vessel Vityaz that discovered it in 1958.

Geography
It is north east of Vanuatu with a greatest depth of 6.1 km but can be as shallow as 3.5 km.

To its south east there are three discontinuous and elongated troughs called respectively the Alexa, Rotuma and Horne Troughs. They connect the Vityaz Trench via what is termed the Vitiaz Trench Lineament to the northern end of the Tonga Trench.

Tectonics
It was formed during the middle Neogene (activity stopped about 8 million years ago), when its location was the then convergent plate boundary between the Pacific and Indo-Australian Plates. At this time the Vitiaz Arc was a continuous east-facing volcanic arc extending from the region of Tonga to the region of the Solomon Islands. Now it is inactive (i.e. fossil) but has geological importance as it separates the northern Cretaceous crust of the Pacific Plate from the Cenozoic basalts of the North Fiji and Lau Basins. To its south west is the East Melanesian Rise and onward, deep under the present North Fiji Basin is a zone of deep earthquakes believed to be associated with the slab of Pacific Crust subducted previously at the trench.