TheCaroline plate is a minortectonic plate that straddles the Equator in theeastern hemisphere located north ofNew Guinea. It forms asubduction zone along the border with theBird's Head plate and other minor plates of theNew Guinea region to the south. A transform boundary forms the northern border with thePacific plate. Along the border with thePhilippine Sea plate is aconvergent boundary that transitions into arift.

Caroline plate
The Caroline plate is shown with red shading in this map of local tectonic features from Bird's 2003 model.[1] Further definition of some of the plate boundaries implied in the map has occurred in the southeast since.[2]
Type	Minor
Approximate area	1,700,000 km2[3]
Movement1	north-west
Speed1	87 mm/year
Features	Pacific Ocean
1Relative to theAfrican plate

The Caroline plate was first proposed as a distinct plate byWeissel & Anderson 1978.

A separateterrane with its own tectonic history, the Caroline plate has been considered part of thePacific plate because of sparse seismicity and low velocities along its boundaries. It includes theWest andEast Caroline basins and the inactiveEauripik Rise separating them, but neither theCaroline Islands nor theCaroline Ridge. It is subducting under theBird's Head and the plates or blocks associated with the presentAustralian plate along theNew Guinea Trench to the south.^[1][4]

The boundary with thePhilippine Sea to the west has two segments: the southern segment, theAyu Trough was spreading at a rate of 8 mm/yrc. 25–2 Ma but has been slowing down since. The northern segment, thePalau and southernYap trenches, is not an active subduction zone as indicated by the lack of activevolcanoes. The Caroline-Pacific boundary is a complex, evolving system partly and potentially developing into a subduction zone. The south-east boundary, along theManus Trench, is a convergent boundary, but in the absence of active volcanoes and earthquakes, is not a subduction zone at present.^[1] This is the boundary of the Caroline plate with theNorth Bismarck plate, which is believed to be a relic plate currently moving with the Pacific plate.^[5][4] Beyond the North Bismarck plate to the south is an area with currently actively independently moving microplates such as theSouth Bismarck plate, theSolomon Sea plate and theWoodlark plate.^[2]

The Caroline plate moves at velocities very close to those of the Pacific plate and its age of formation and current status as an independent plate are uncertain. There is a very slow rate of spreading between the Caroline and Philippine plates but the Caroline plate apparently moved together with both the Philippine and New Guinea plates during the Neogene.^[6]

The Caroline Ridge, to the north, meets the Caroline plate at the Sorol Trough at which there some evidence of oblique extension; the Caroline Ridge, however, is, although of uncertain origin, made of oceanic crust and probably the product of a hotspot. The presence of a trench and indications of subduction beneath the Pacific plate is suggestive but the absence of island arcs, which could be expected from substantial subduction in the past, makes the development along this boundary unclear.^[6]

The Caroline plate was, under all circumstances, a separate plate in the past. The boundary along its eastern side, the Mussau Trench, must have been an important boundary since magnetic anomalies on the Caroline plate are Oligocene but those on the Pacific plate Cretaceous. There are indications of spreading in the Caroline Sea 34–27 Ma. If the Caroline plate moved with the Pacific plate there should be clear evidences of a corresponding subduction beneath New Guinea, of which there is virtually none. The Ayu Trough is a slow spreading zone that opened 15 Ma.^[6]

Before about 6 million years ago as theOntong Java Plateau andIndo-Australian plate collided theBismarck Sea was initially formed as a back-arc basin behind the New Britain arc, and after the collision, a transpressional zone developed in what is now the west Bismarck Sea, associated with subduction of the Caroline plate andNorth Bismarck plate at the New Guinea Trench.^[4]