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| Amundsen Plate | |
|---|---|
| Name | Amundsen Plate |
| Type | Microplate |
| Area km2 | 250000 |
| Coordinates | 72°S 120°W |
| Region | Southern Ocean, Antarctica |
| Status | Proposed, microplate |
| Discovered | 1990s |
| Boundary | Pacific Plate; Antarctic Plate; Scotia Plate; South American Plate |
Amundsen Plate
The Amundsen Plate is a small tectonic microplate located in the Southern Ocean adjacent to West Antarctica and the Amundsen Sea. Proposed from marine geophysical and satellite geodesy studies, it occupies an area near the continental margin of Marie Byrd Land, lying between the Pacific Plate, Antarctic Plate, Scotia Plate, and the extensional regime of the Bellingshausen Sea. Its identification has implications for models of Antarctic rifting, West Antarctic Rift System, and regional paleoceanography.
The Amundsen Plate lies at the southern end of the East Pacific Rise-influenced domain where fragments of the Phoenix Plate and remnants of the Farallon Plate interacted with the southern margin of the Antarctic Peninsula. The plate overlies oceanic crust of variable age and thin continental lithosphere associated with Marie Byrd Land, the Ross Sea Rift, and the Amundsen Sea Embayment. Local geology records interactions among the West Antarctic Rift System, Transantarctic Mountains tectonism, and the breakup processes that separated Gondwana fragments including the Tasman Sea opening and the South Atlantic Ocean spreading. Bathymetric highs and fracture zones on the plate reflect inherited structures from the Phoenix Ridge and extinct spreading centers.
Boundaries proposed for the Amundsen Plate include transform-like fault systems, diffuse shear zones, and abandoned spreading axes. To the west it approaches the transform-linked structures associated with the Pacific-Antarctic Ridge and the extinct traces of the Phoenix Plate subduction. To the east it grades into the diffuse boundary with the Scotia Plate and the South American Plate via fracture zones that connect to the South Sandwich Trench and the Magallanes-Fagnano Fault. Numerous named and unnamed fracture zones, including offsets correlated with magnetic anomaly patterns, have been mapped by surveys from British Antarctic Survey, United States Antarctic Program, Lamont–Doherty Earth Observatory, and GEOMAR. The plate margin is characterized by segmented fault strands comparable to the Gakkel Ridge transform domain and the Chile Triple Junction complexity.
Kinematic models infer slow, complex motions for the Amundsen Plate relative to adjacent plates, derived from analyses combining seafloor magnetic anomalies, satellite altimetry, and GNSS data from coastal Antarctic stations such as those maintained by Scientific Committee on Antarctic Research and national programs including Australian Antarctic Division. Reconstructions suggest weak clockwise rotation relative to the Antarctic Plate with velocities on the order of a few millimeters per year, similar to motions inferred for other microplates like the Shetland Plate and the Adriatic Plate. The plate’s motion history is tied to changes in spreading rates at the East Pacific Rise and to migration of the Chile Triple Junction, influencing strike-slip kinematics and episodic extension.
The Amundsen Plate evolved during late Mesozoic to Cenozoic rifting that accompanied the breakup of Gondwana and the dispersal events that formed the Southern Ocean basins including the Drake Passage opening and the separation of India and Antarctica. Paleogeographic reconstructions link its formation to the cessation of spreading on the Phoenix Plate and subsequent reorganization during the Paleogene, when plate boundary relocations influenced the Antarctic Circumpolar Current inception and Oligocene cooling events. Sedimentary sequences imaged along the plate margin record uplift and subsidence associated with glacial-interglacial cycles documented by cores collected by the International Ocean Discovery Program and by expeditions such as those of USCGC Polar Star and research vessels operated by NIWA.
Seismicity on and near the Amundsen Plate is generally low but includes localized earthquakes related to transform faulting and intraplate deformation, cataloged by networks operated by IRIS and the Global Seismographic Network. Volcanic evidence is sporadic, with acoustic and dredge samples indicating alkaline to tholeiitic volcanism possibly linked to mantle upwelling episodes contemporaneous with the West Antarctic Rift System volcanism and seamounts akin to those on the Pacific Plate margin. Potential interactions with mantle plumes hypothesized for Marie Byrd Land and the putative Balleny microplate dynamics remain active research topics.
Investigations of the Amundsen Plate combine marine geophysical surveys, magnetic anomaly mapping, multibeam bathymetry, and seismic reflection/refraction conducted by institutions including British Antarctic Survey, Lamont–Doherty Earth Observatory, Scripps Institution of Oceanography, and national Antarctic programs from New Zealand, Argentina, United States, and Australia. Satellite geodesy using GPS and satellite altimetry from missions such as ERS-1, TOPEX/Poseidon, and CryoSat-2 complement shipborne studies. Paleomagnetic data, dredged rock analyses, and borehole records from initiatives like the ANDRILL and the Integrated Ocean Drilling Program inform plate reconstructions, while numerical modeling performed at centers like WHOI and GFZ Potsdam tests kinematic scenarios. Ongoing collaborative projects under the auspices of SCAR and international partnerships aim to refine the plate’s boundaries, motion rates, and its role in Antarctic geodynamics.