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Geologic Context
The North Bismarck, Manus, and South Bismarck microplates are overlain by the Bismarck Archipelago and Bismarck Sea. The Bismarck Archipelago, which formed from an oceanic volcanic arc, is a crescent-shaped array of islands including New Britain Island, New Ireland, New Hanover, and Manus Island, among many others. The Archipelago is made up of Eocene to Oligocene aged volcanic rocks containing diorite to granodiorite intrusions, with some areas partly covered by Miocene limestones and Pliocene to Quaternary sediments. Some volcanoes within the Archipelago are still active (Davies, 2012).
The Caroline plate is located to the northwest of the Bismarck region, and is virtually entirely covered by Pacific Ocean. Both the Caroline plate and the North Bismarck plate were considered part of the Pacific plate in many past plate models, but subsequent studies of seafloor morphology and geophysical characteristics have shown them to be separate plates (Weissel and Anderson, 1978).
The North Bismarck, Manus, and South Bismarck microplates are overlain by the Bismarck Archipelago and Bismarck Sea. The Bismarck Archipelago, which formed from an oceanic volcanic arc, is a crescent-shaped array of islands including New Britain Island, New Ireland, New Hanover, and Manus Island, among many others. The Archipelago is made up of Eocene to Oligocene aged volcanic rocks containing diorite to granodiorite intrusions, with some areas partly covered by Miocene limestones and Pliocene to Quaternary sediments. Some volcanoes within the Archipelago are still active (Davies, 2012).
The Caroline plate is located to the northwest of the Bismarck region, and is virtually entirely covered by Pacific Ocean. Both the Caroline plate and the North Bismarck plate were considered part of the Pacific plate in many past plate models, but subsequent studies of seafloor morphology and geophysical characteristics have shown them to be separate plates (Weissel and Anderson, 1978).
Caroline plate
The ocean floor on the Caroline plate is determined to be of Oligocene age, based on magnetic anomaly lineations (Larson and Schlanger, 1981). It rotates 0.3°/Ma around a pole at 10.13°N, -45.57°E (Seno et al., 1993). For information on the formation of the Caroline plate, see Western Microplate Formations and Projections (General Pages). The Caroline plate is surrounded by a large variety of boundaries. To the west, it border with the Philippine Sea plate has both a divergent boundary to the south, and a convergent boundary to the north, with no evidence for current subduction (Bird, 2003). To the northeast, there’s a long transform boundary with the Pacific plate, and to the east, the boundary becomes convergent, delineated by the young Mussau Trench (Hegarty and Weissel, 1988). To the southwest, where the plate is in contact with the North Bismarck plate, the border is shown by the Manus Trench, an extinct subduction zone (Bird, 2003). The Caroline plate’s southern border, with the Birds Head and Woodlark plates, is a convergent boundary where the Caroline plate is subducting southwards into the New Guinea Trench (Bird, 2003). North Bismarck plate The North Bismarck plate contains the northern islands of the Bismarck Archipelago, and rotates 0.3°/Ma around a pole at -4.00°N, 139.00°E (Tregoning et al., 1998). To the North, its border with both the Caroline and the Pacific plates is outlined by the Manus Trench, which is a convergent boundary and extinct subduction zone. The Western border is marked by the subduction of the North Bismark plate beneath the Woodlark plate, into the New Guinea Trench. To the South, the North Bismarck plate is separated from the South Bismarck and Manus plates dominantly by sinistral transform boundaries (Bird, 2003). South Bismarck plate The South Bismarck plate contains the Southern islands of the Bismack Archipelago, and rotates 8.4°/Ma around a pole at 10.61°N, -32.99°E (Tregoning et al., 1999). Its seafloor is determined to be of Cenozoic age (Larson and Schlanger, 1981). To the North, it is separated from the North Bismarck plate by transform boundaries, including the Willaumez, Djaul, and Weitin Transforms, and step-over rift zones. To the southeast its border with the Solomon Sea plate is marked by the New Britain Trench, where the Solomon Sea plate is being subducted northwards into the trench (Bird, 2003). |
Manus plate
The Manus microplate is a young, small, 100-km scale plate that formed in a step-over between transform boundaries separating the North and South Bismarck plates. The left-lateral motion of these plates is causing rapid counter-clockwise pivoting of the Manus microplate (Martinez and Taylor, 1996). Its rate of rotation around a pole of -3.04°N, 150.46°E is 51°/Ma, which is possibly the most rapid relative rotation on Earth currently (Bird, 2003). The Manus microplate formed during the Brunhes chron, indicating a maximum age of 780,000 years. It is made up of young mid-ocean ridge basalt as well as some older oceanic floor broken off from the South Bismarck plate. Its northeast and southwest borders, with North Bismarck and South Bismarck plates respectively, are both convergent boundaries, and its northwest and southeast borders, also with North Bismarck and South Bismarck plates respectively, are both divergent boundaries (Martinez and Taylor, 1996).
References
Bird, P., 2003. An updated digital model of plate boundaries, Geochemistry, Geophysics, Geosystems, 4, 3, 1-52.
Davies, H. L., 2012. The geology of New Guinea - the cordilleran margin of the Australian continent. Episodes, 35, 1, 87-103.
Hegarty, K. A. and J. K. Weissel, 1988. Complexities in the development of the Caroline plate region, Western Equatorial Pacific in The Ocean Basin and Margins, New York, Springer, pp. 277-301.
Larson, R.L., and Schlanger, S.O., 1981. Geological evolution of the Nauru Basin and regional implications. Initial Reports of Deep Sea Drilling Project, Vol. 61, pp. 841-862.
Martinez, F., and B. Taylor, 1996. Fast backarc spreading, rifting, and microplate rotation, between transform faults in the Manus Basin, Bismarck Sea, Mar. Geophy. Res., 18, 203– 224.
Tregoning, P., et al., 1998. Estimation of current plate motions in Papua New Guinea from Global Positioning System observations, J. Geophys. Res., 103, 12,181–12,203.
Tregoning, P., R. J. Jackson, H. McQueen, K. Lambeck, C. Stevens, R. P. Little, R. Curley, and R. Rosa, 1999. Motion of the South Bismarck plate, Papua New Guinea, Geophys. Res. Lett., 26, 3517–3520.
Seno, T., S. Stein, and A. E. Gripp, 1993. A model for the motion of the Philippine Sea plate consistent with NUVEL-1 and geological data, J. Geophys. Res., 98, 17,941–17,948.
Waring, G. A., 1965. Thermal Springs of the United States and Other Countries of the World- A Summary. Geological Survey Professional Paper 492.
Weissel, J. K., and R. Anderson, 1978. Is there a Caroline plate? Earth Planet. Sci. Lett., 41, 143–158.
Bird, P., 2003. An updated digital model of plate boundaries, Geochemistry, Geophysics, Geosystems, 4, 3, 1-52.
Davies, H. L., 2012. The geology of New Guinea - the cordilleran margin of the Australian continent. Episodes, 35, 1, 87-103.
Hegarty, K. A. and J. K. Weissel, 1988. Complexities in the development of the Caroline plate region, Western Equatorial Pacific in The Ocean Basin and Margins, New York, Springer, pp. 277-301.
Larson, R.L., and Schlanger, S.O., 1981. Geological evolution of the Nauru Basin and regional implications. Initial Reports of Deep Sea Drilling Project, Vol. 61, pp. 841-862.
Martinez, F., and B. Taylor, 1996. Fast backarc spreading, rifting, and microplate rotation, between transform faults in the Manus Basin, Bismarck Sea, Mar. Geophy. Res., 18, 203– 224.
Tregoning, P., et al., 1998. Estimation of current plate motions in Papua New Guinea from Global Positioning System observations, J. Geophys. Res., 103, 12,181–12,203.
Tregoning, P., R. J. Jackson, H. McQueen, K. Lambeck, C. Stevens, R. P. Little, R. Curley, and R. Rosa, 1999. Motion of the South Bismarck plate, Papua New Guinea, Geophys. Res. Lett., 26, 3517–3520.
Seno, T., S. Stein, and A. E. Gripp, 1993. A model for the motion of the Philippine Sea plate consistent with NUVEL-1 and geological data, J. Geophys. Res., 98, 17,941–17,948.
Waring, G. A., 1965. Thermal Springs of the United States and Other Countries of the World- A Summary. Geological Survey Professional Paper 492.
Weissel, J. K., and R. Anderson, 1978. Is there a Caroline plate? Earth Planet. Sci. Lett., 41, 143–158.