Halmahera plate has recently (1990s) been postulated to be a microplate within the Molucca Sea Collision Zone of eastern Indonesia.
It is the only global example of an active arc-arc collision consuming an oceanic basin via subduction in two directions.
[1] Seismicity shows the east-dipping Halmahera reaches a depth of about 200 km.
[1] Both Sangihe and Halmahera are exposed to the surface while the Molucca Sea plate is completely subsumed below these two microplates.
[1] 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.