Halmahera Plate
Encyclopedia
Halmahera Plate has recently (1990s) been postulated to be a microplate within the Molucca Sea Collision Zone
of eastern Indonesia
.
region is unique. It is the only global example of an active arc-arc collision consuming an oceanic basin via subduction
in two directions. The Molucca Sea Plate
has been subsumed by tectonic microplates, the Halmahera Plate and the Sangihe Plate
. The whole complexity is now known as the Molucca Sea Collision Zone
.
The existence of Halmahera as a tectonic plate separate from the Molucca Sea Plate
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
between 45 Ma and 25 Ma.
Seismicity
shows the east-dipping Halmahera reaches a depth of about 200 km. Seismic tomography
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 and the Australian Plate, 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 Australian Plate.
A broad high-velocity zone beneath the Bird's Head Plate
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
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
, a major lateral east-west fault.
An earlier model considered the area to be the Halmahera Arc
, 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.
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:...
of eastern Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
.
Regional tectonics
The tectonic setting of the Molucca SeaMolucca Sea
The Molucca Sea is located in the western Pacific Ocean, within the country of Indonesia. The region is rich in coral and has many diving sites.-Location:...
region is unique. It is the only global example of an active arc-arc collision consuming an oceanic basin via subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
in two directions. The Molucca Sea Plate
Molucca Sea Plate
-Earlier theory:The Molucca Sea Plate was theorised to be a small tectonic plate carrying northern Sulawesi, the Molucca Sea and a portion of the Banda Sea in a region littered with numerous small plates. The theory suggested a subduction zone lies along its northern border with the Sunda Plate...
has been subsumed by tectonic microplates, the Halmahera Plate and the Sangihe Plate
Sangihe Plate
Sangihe Plate has recently been postulated to be a microplate within the Molucca Sea Collision Zone of eastern Indonesia.-Regional tectonics:...
. The whole complexity is now known as the Molucca Sea Collision Zone
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 existence of Halmahera as a tectonic plate separate from the Molucca Sea Plate
Molucca Sea Plate
-Earlier theory:The Molucca Sea Plate was theorised to be a small tectonic plate carrying northern Sulawesi, the Molucca Sea and a portion of the Banda Sea in a region littered with numerous small plates. The theory suggested a subduction zone lies along its northern border with the Sunda Plate...
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
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...
between 45 Ma and 25 Ma.
Seismicity
Seismology
Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic,...
shows the east-dipping Halmahera reaches a depth of about 200 km. Seismic tomography
Seismic tomography
Seismic tomography is a methodology for estimating the Earth's properties. In the seismology community, seismic tomography is just a part of seismic imaging, and usually has a more specific purpose to estimate properties such as propagating velocities of compressional waves and shear waves . It...
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 and the Australian Plate, 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 Australian Plate.
A broad high-velocity zone beneath the Bird's Head Plate
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 & Müller consider it to be moving in unison with the Pacific Plate. Bird considers it to be unconnected to the Pacific Plate. The plate is separating from...
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
Celebes Sea
The Celebes 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 the Sangihe Islands chain, on the south by Sulawesi, and on the west by Kalimantan in Indonesia...
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
Sorong fault also 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 Plate, Bird's Head Plate, Halmahera Plate and the Molucca Sea Plate. It has...
, a major lateral east-west fault.
An earlier model considered the area to be the Halmahera Arc
Halmahera Arc
Halmahera Arc is the volcanic arc of the Halmahera region of eastern Indonesia. It is considered to belong to the Halmahera Plate tectonics, within the Molucca Sea Collision Zone.-Origin:...
, 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.