| Molucca Sea plate | |
|---|---|
 | |
| Type | Minor |
| Movement1 | north |
| Speed1 | 30-40 mm/year[1][2] |
| Features | Sulawesi,Molucca Sea |
| 1Relative to theAfrican plate | |
Located in the western Pacific Ocean near Indonesia, theMolucca Sea plate has been classified by scientists as a fully subducted microplate that is part of theMolucca Sea Collision Complex. The Molucca Sea plate represents the only known example ofdivergent double subduction (DDS), which describes the subduction on both sides of a single oceanic plate.[3]
The Molucca Sea plate is one of many tectonic features that compose the Molucca Sea Collision Complex, which refers to the tectonic relationship of theSangihe plate,Halmahera plate, and the Molucca Sea plate, in addition to the volcanicHalmahera andSangihe Arcs. The southeast movingSangihe plate is situated along the western boundary of the Molucca Sea plate. The northwest movingHalmahera plate is situated along the eastern boundary of the Molucca Sea plate. In the westernPacific Ocean, theMolucca Sea is bordered by the Indonesian Islands of Celebes (Sulawesi) to the west,Halmahera to the east, and the Sula Islands to the south. The Molucca Sea borders theBanda Sea to the south and theCelebes Sea to the west. To the north is thePhilippine Sea and to the east is theHalmahera Sea. Situated south ofMindanao, the Molucca Sea is a narrow basin underlined by a north‐southophiolitic ridge, which uplifts the central region of the basin.[4]
While the scientific community has not come to a consensus as to when the Molucca Sea plate became fully subducted, the dominant theory is that the Molucca Sea plate has been completely subducted beneath the overridingHalmahera andSangihe plates.[3] When actively subducting, the crustal collision of the Molucca Sea plate was formed by surface intersection of "oppositely dippingBenioff zones” (also known as divergent double subduction) which results in theSangihe and Halmaheravolcanic arcs.[4] The force exerted by the thick overlying collision complex of the Halmahera and Sangihe plates effectively depressed the crust of the Molucca Sea plate.[5] The plate itself features an asymmetrical morphology, configured in an inverted U-shape. The arc-arc collision zone of the Molucca Sea plate is characterized as a thick, low velocity layer, which is highly variable in density.[3][6] The variable in density of the Molucca Sea plate led to different subduction velocities on the two sides.[3]Divergent Double Subduction may facilitate various tectonic processes, including closure of ocean basins,accretion and amalgamation of volcanic arcs, and growth of continents.[3]
Historically, the Molucca Sea plate has experienced hundreds of earthquakes ranging in magnitude.[4] The most recent large earthquake occurred in January 2017 when a 7.3 magnitude earthquake deep beneath theCelebes Sea, which the USGS attributed to the “deep reverse faulting within the inclined seismic zone defining the deep limit of the Molucca Sea microplate beneath the Celebes Sea Basin.”[7]
The geologic characteristics displayed on the surrounding islands provide insight regarding the complex plate movement of thedivergent double subducting plate. Detachedophiolitic series and thickmelanges are overlain byforearc deposits; subduction-driven east–west shortening of the Snellius Plateau caused the thrustmelanges to reactivate and deform theforearc series.[8] Exposedophiolitic rocks can be found on the islands of the submarine Talaud-Mayu Ridge, which bisects the arc-arc collision zone of the Molucca Sea plate; theseophiolites provide insight regarding the relationship between earthquakes and uplift surrounding the plate.[9]
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