The Molucca Sea Collision Zone is postulated by paleogeologists to explain the tectonics

Tectonics

Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...

 of the area based on the Molucca Sea

Molucca 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:...

 in 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...

, and adjacent involved areas.

Tectonics

The tectonic relationship of 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:...

, Halmahera Plate

Halmahera Plate

Halmahera Plate has recently been postulated to be a microplate within the Molucca Sea Collision Zone of eastern Indonesia.-Regional tectonics:...

, and 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...

, plus the volcanic 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:...

 and the Sangihe Arc is complex. Their interrelationship constitutes the Molucca Sea Collision Zone. The north of this zone interlinks with the Philippine Mobile Belt

Philippine Mobile Belt

The Philippine Mobile Belt is a complex portion of the tectonic boundary between the Eurasian Plate and the Philippine Sea Plate, comprising most of the country of the Philippines. It includes two subduction zones, the Manila Trench to the west and the Philippine Trench to the east, as well as the...

. Some call this linkage the Philippine-Halmahera Arc and consider it an integral part of the elongated zone of convergence extending north through the Philippines

Philippines

The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

 into eastern Taiwan

Taiwan

Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...

. In the Molucca Sea Collision Zone model, the Molucca Sea Plate has been totally consumed by the arc-arc collision of the Halmahera Arc and the Sangihe Arc 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...

.

Arc-arc collision

The Molucca Sea Collision Zone is the site of an orthogonal collision between two active subduction systems. Both the Halmahera subduction system to the east, and the Sangihe subduction system to the west, have subducted oceanic lithosphere

Lithosphere

The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...

 of the Molucca Sea plate, which has been completely consumed, with the Sangihe arc now over-riding the Halmahera forearc. Both volcanic arcs have been active since 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...

. Both arcs show increased evidence for sediment recycling as the collision progressed, but for differing reasons. In Halmahera, this may represent an increased sediment flux through the arc front, while in Sangihe it may simply reflect a greater opportunity for melting of sediment-fluxed portions of the mantle wedge. In both cases the change in arc geochemistry can be related to the evolving architecture of that particular 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"...

 zone. The Halmahera lavas also record a temporal change in the chemistry of the mantle

Mantle (geology)

The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....

 component that resulted from induced convection above the falling Molucca Sea Plate drawing compositionally distinct peridotite

Peridotite

A peridotite is a dense, coarse-grained igneous rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium, reflecting the high proportions of magnesium-rich olivine, with appreciable iron...

 into the mantle wedge.

Single collision zones

The magmatic systems are reaching the end of their life as island arcs and are becoming a single collision zone, lending weight to the contention that Halmahera and Sangihe should be regarded as tectonic plates rather than volcanic arcs.

Northern extension

Seismic and tomographic discrepancies in the mantle up to 400 km below Mindanao

Mindanao

Mindanao is the second largest and easternmost island in the Philippines. It is also the name of one of the three island groups in the country, which consists of the island of Mindanao and smaller surrounding islands. The other two are Luzon and the Visayas. The island of Mindanao is called The...

in the Philippines, indicate it is a more advanced northern extension of the Molucca Sea Collision Zone.