Halmahera Plate has recently (1990s) been postulated to be a

microplate A microplate, also known as a microtiter plate (''Microtiter'' is a registered trademark in the United States, therefore it should not be used generically without attribution), microwell plate or multiwell, is a flat plate with multiple "wells" ...

within the

Molucca Sea Collision Zone The Molucca Sea Collision Zone is postulated by paleogeologists to explain the tectonics of the area based on the Molucca Sea in Indonesia, and adjacent involved areas. Tectonics The tectonic relationship of the Sangihe Plate, Halmahera Plate, a ...

of eastern

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...

Regional tectonics

The tectonic setting of the

Molucca Sea The Molucca Sea (Indonesian: ''Laut Maluku'') is located in the western Pacific Ocean, around the vicinity of Indonesia, specifically bordered by the Indonesian Islands of Celebes (Sulawesi) to the west, Halmahera to the east, and the Sula Islan ...

region is unique. It is the only global example of an active arc-arc collision consuming an oceanic basin via

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

in two directions. The

Molucca Sea Plate Located in the western Pacific Ocean near Indonesia, the Molucca Sea Plate has been classified by scientists as a fully subducted microplate that is part of the Molucca Sea Collision Complex. The Molucca Sea Plate represents the only known example ...

has been subsumed by tectonic microplates, the Halmahera Plate and the

Sangihe Plate Sangihe Plate has recently (1990s) been postulated to be a microplate within the Molucca Sea Collision Zone of eastern Indonesia. Regional tectonics The tectonic setting of the Molucca Sea region is unique. It is the only global example of an acti ...

. The whole complexity is now known as the

. The existence of Halmahera as a tectonic plate separate from the

is not yet entirely agreed upon by paleogeologists. Some see Halmahera as an eastern slab of the Molucca Sea Plate, just as they regard Sangihe as a western slab of the Molucca Sea Plate. What is apparent to date is that Halmahera was part of the Molucca Sea slab subducted during the

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...

between 45 Ma and 25 Ma.R. Hall and W. Spakman, ''Australian Plate Tomography and Tectonics'' in R. R. Hillis, R. D. Müller, ''Evolution and Dynamics of the Australian Plate,'' Geological Society of America Special Papers 2003, #372, p377

Seismicity Seismicity is a measure encompassing earthquake occurrences, mechanisms, and magnitude at a given geographical location. As such, it summarizes a region's seismic activity. The term was coined by Beno Gutenberg and Charles Francis Richter in 19 ...

shows the east-dipping Halmahera reaches a depth of about 200 km.

Seismic tomography Seismic tomography or seismotomography is a technique for imaging the subsurface of the Earth with seismic waves produced by earthquakes or explosions. P-, S-, and surface waves can be used for tomographic models of different resolutions based on ...

suggests that the Halmahera goes deeper to at least 400 km. Both Sangihe and Halmahera are exposed to the surface while the Molucca Sea plate is completely subsumed below these two microplates. The southern boundary of the Molucca Sea Plate is also the boundary of the

Philippine Sea Plate The Philippine Sea Plate or the Philippine Plate is a tectonic plate comprising oceanic lithosphere that lies beneath the Philippine Sea, to the east of the Philippines. Most segments of the Philippines, including northern Luzon, are part of ...

and the

Australian Plate The Australian Plate is a major tectonic plate in the eastern and, largely, southern hemispheres. Originally a part of the ancient continent of Gondwana, Australia remained connected to India and Antarctica until approximately when India broke ...

, and is moving northwards. Since the Sangihe Plate and the Halmahera Plate are in continuity with the Molucca Sea Plate, this implies all three slabs are moving northward in mantle with the

. A broad high-velocity zone beneath the

Bird's Head Plate The Bird's Head Plate is a minor tectonic plate incorporating the Bird's Head Peninsula, at the western end of the island of New Guinea. Hillis and Müller consider it to be moving in unison with the Pacific Plate. Bird considers it to be unconne ...

at 400–600 km depth is interpreted by R Hall and W Spakman as indicating a remnant slab subducted below the Halmahera Plate, and another broad high-velocity zone beneath the

Celebes Sea The Celebes Sea, (; ms, Laut Sulawesi, id, Laut Sulawesi, fil, Dagat Selebes) or Sulawesi Sea, of the western Pacific Ocean is bordered on the north by the Sulu Archipelago and Sulu Sea and Mindanao Island of the Philippines, on the east by ...

at 700–1000 km depth is interpreted as a remnant slab below the Sangihe Plate, both remnants having originated from a slab subducted beneath the Philippine-Halmahera Arc 45 Ma to 25 Ma ago. In this model, the Bird's Head and Halmahera Plates are separated by the

Sorong Fault Sorong fault also (Sorong Fault Zone, SFZ) is an active, broad zone of inferred left lateral shear at the triple junction of the Australian plate, Eurasian plate, and Pacific plates, where many plate fragments exist, such as the Philippine Sea Pl ...

, a major lateral east-west fault. An earlier model considered the area to be the

Halmahera Arc Halmahera Arc is the volcanic arc of the Halmahera region of eastern Indonesia. It is considered to belong to the Halmahera Plate within the Molucca Sea Collision Zone. Origin Potassium-argon ages of Neogene to Recent igneous rocks from the Halmah ...

, a volcanic arc of islands without a tectonic plate base. More recent studies in the 1990s and later, have displaced this theory with the Halmahera Plate theory.

References

{{DEFAULTSORT:Halmahera Plate Tectonic plates Geology of the Pacific Ocean Geology of Indonesia Geology of the Philippines Molucca Sea

Regional tectonics

See also

References