West Melanesian Trench

Oceanic trench in the Bismarck Sea north of Papua New Guinea

New Britain

Manus
Island

Bismarck Archipelago

New
Guinea

Solomon
Sea

Melanesian
West Trench

Manus
Basin

New Guinea
Trench

Mussau
Trough

New
Britain
Trench

Seafloor topographic map of area of West Melanesian Trench. The labelled New Guinea and New Britain trenches are the nearest now definitely actively subducting ocean trenches.

Approximate surface projection on Pacific Ocean of the relic (ie currently not actively subducting) West Melanesian Trench. While other related relic trenches (light blue) are shown for context, active trenches nearby, which are to the south are not. Click, then mouse-over shows feature names.

The West Melanesian Trench^[1] (previously known as Manus Trench)^[2] is an oceanic trench in the Bismarck Sea north of Papua New Guinea delineating the plate tectonic boundary between the Caroline and North Bismarck plates. ^[3]

There is only slight seismic activity along both the trench, and its status as an active subduction zone, as proposed in the 2003 general model of major plate movement,^[4] is not generally accepted now.^[5] A relative motion of 1 cm/year (0.39 in/year) or less has, nevertheless, been suggested for the trench, roughly normal to the trench.^[3]

The Kilinailau Trench east of New Ireland appears to form a continuation to the south west and is thought to mark the boundary between the Pacific and North Bismarck plates. It is, however, disputed whether the Caroline Plate moves independently from the Pacific Plate. If not, the West Melanesian and Kilinailau trenches form the Pacific-North Bismarck boundary together.^[3] The area to the western end of the trench is actively subducting under the Australian Plate at the New Guinea Trench.^[5]

Perpendicular to the two trenches is another trench, the Mussau Trough separating the Caroline Plate and Pacific Plate. This areas tectonics is still poorly understood.^[5]

References

^ "Marine Gazetteer:West Melanesian Trench". Retrieved 4 October 2023.
^ Note:Also known as Manus Trough or the Melanesian Trench, the later is particularly confusing as the Vityaz Trench has been named the East Melanesian Trench.
^ ^a ^b ^c Tregoning 2002, North Bismarck/Pacific Boundary, p. 6.
^ Bird 2003, 5.10. North Bismarck Plate (NB), South Bismarck Plate (SB), and Manus Plate (MN).
^ ^a ^b ^c Holm, Rosenbaum & Richards 2016, p. 68.

Sources

Tregoning, P. (2002). "Plate kinematics in the western Pacific derived from geodetic observations" (PDF). Journal of Geophysical Research: Solid Earth. 107 (B1): ECV 7-1-ECV 7-8. Bibcode:2002JGRB..107.2020T. doi:10.1029/2001JB000406. Retrieved 7 January 2015.
Holm, RJ; Rosenbaum, G; Richards, SW (1 May 2016). "Post 8 Ma reconstruction of Papua New Guinea and Solomon Islands: Microplate tectonics in a convergent plate boundary setting". Earth-Science Reviews. 156: 66–81. doi:10.1016/j.earscirev.2016.03.005.
Bird, P. (2003). "An updated digital model of plate boundaries". Geochemistry, Geophysics, Geosystems. 4 (3): 1027. Bibcode:2003GGG.....4.1027B. doi:10.1029/2001GC000252.

Tectonic plates of Southeast Asia–New Guinea (Australian Plate–Pacific Plate Convergence Zone)

Large

Small

West	Burma Plate
Philippines	Philippine Mobile Belt
Indonesia	Banda Sea Plate Bird's Head Plate Halmahera Plate Molucca Sea Collision Zone Molucca Sea Plate Sangihe Plate Timor Plate
New Guinea	Maoke Plate North Bismarck Plate Manus Plate Solomon Sea Plate South Bismarck Plate Trobriand Plate Woodlark Plate

Faults

Trenches
and troughs

Java Trench (Sunda) with Mentawai Trough Sunda Trough Timor Trough
Philippines	Cotabato Trench Manila Trench North Luzon Trough Negros Trench Palawan Trench Philippine Trench East Luzon Trench Sulu Trench
Sulawesi and Moluccas	Aru Trough Banda Trench Ceram Trough Salajar Trough Sangihe Trough Talaud Trough Ternate Trough
Timor	Aur Trough Tanimbar Trough
New Guinea	Ayu Trough Kilinailau Trench Manokwari Trough Lyra Trough Mussau Trough New Guinea Trench Pocklington Trough New Britain Trench (Bougainville) West Caroline Trough West Melanesian Trench