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, and the Molucca Sea Plate, plus the volcanic Halmahera Arc 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. 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 into eastern Taiwan. 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.^[1]

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 of the Molucca Sea plate, which has been completely consumed, with the Sangihe arc now over-riding the Halmahera forearc.^[2] Both volcanic arcs have been active since the Neogene. 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 zone. The Halmahera lavas also record a temporal change in the chemistry of the mantle component that resulted from induced convection above the falling Molucca Sea Plate drawing compositionally distinct peridotite into the mantle wedge. ^[3]

Single collision zones

The magmatic systems are reaching the end of their life as island arcs and are becoming a single collision zone,^[4] 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 in the Philippines, indicate it is a more advanced northern extension of the Molucca Sea Collision Zone. ^[5]

References

1. ^ Macpherson, Forde, Hall and Thirlwall (2003) in Intra-Oceanic Subduction Systems: Tectonic and Magmatic Processes, ISBN 1-86239-147-5 p208
2. ^ Colin G Macpherson et ors, Geochemical evolution of magmatism in an arc-arc collision: the Halmahera and Sangihe arcs, eastern Indonesia, in Robert D Larter, ed, (2003) Intra-oceanic Subduction Systems, Geological Society of London. p208
3. ^ Colin G Macpherson et ors, Geochemical evolution of magmatism in an arc-arc collision: the Halmahera and Sangihe arcs, eastern Indonesia, in Robert D Larter, ed, (2003) Intra-oceanic Subduction Systems, Geological Society of London. p207
4. ^ Colin G Macpherson et ors, Geochemical evolution of magmatism in an arc-arc collision: the Halmahera and Sangihe arcs, eastern Indonesia, in Robert D Larter, ed, (2003) Intra-oceanic Subduction Systems, Geological Society of London. p208
5. ^ Colin G Macpherson et ors, Geochemical evolution of magmatism in an arc-arc collision: the Halmahera and Sangihe arcs, eastern Indonesia, in Robert D Larter, ed, (2003) Intra-oceanic Subduction Systems, Geological Society of London. p215

See also