The Shetland Plate, or South Shetland Plate, is a tectonic microplate located off the tip of the Antarctic Peninsula that contains the

South Shetland Islands The South Shetland Islands are a group of Antarctic islands with a total area of . They lie about north of the Antarctic Peninsula, and between southwest of the nearest point of the South Orkney Islands. By the Antarctic Treaty of 1 ...

. The plate is bordered on three sides by the

Antarctic Plate The Antarctic Plate is a tectonic plate containing the continent of Antarctica, the Kerguelen Plateau, and some remote islands in the Southern Ocean and other surrounding oceans. After breakup from Gondwana (the southern part of the superconti ...

, while the fourth side is bordered by the

Scotia Plate The Scotia Plate () is a Plate tectonics, tectonic plate on the edge of the Atlantic Ocean, South Atlantic and Southern Ocean, Southern oceans. Thought to have formed during the early Eocene with the opening of the Drake Passage that separates ...

. The northwestern border is defined by the South Shetland Trench, separating the Shetland Plate to the south from the Antarctic Plate to the north. This trench is the remnant of a subduction zone where the defunct

Phoenix Plate The Phoenix Plate (also known as the Aluk Plate or Drake Plate) was a tectonic plate that existed during the early Paleozoic through late Cenozoic time. It formed a triple junction with the Izanagi and Farallon plates in the Panthalassa Ocean as ...

, now part of the Antarctic Plate, subducted under the Antarctic Peninsula and the Shetland Islands. The southeastern border is a

rift zone A rift zone is a feature of some volcanoes, especially shield volcanoes, in which a set of linear cracks (or rifts) develops in a volcanic edifice, typically forming into two or three well-defined regions along the flanks of the vent. Believed t ...

, with the Antarctic Plate creating the Bransfield Basin. The southwestern and northeastern boundaries are each part of larger

fracture zone A fracture zone is a linear feature on the ocean floor—often hundreds, even thousands of kilometers long—resulting from the action of offset mid-ocean ridge axis segments. They are a consequence of plate tectonics. Lithospheric plates on eit ...

s. The southwestern border is the Hero Fracture Zone and separates the Antarctic Plate to the southwest from the Shetland Plate to the northeast. The northeastern boundary is the Shackleton Fracture Zone and separates the Shetland Plate to the southwest from the

Geologic history

The Shetland Plate started forming 3 to 4 million years ago. Prior to formation, the Shetland Plate was part of the

adjacent to the Antarctic Peninsula. During this period, the

to the northwest, was

subducting Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

under the Antarctic Peninsula and the

, which created the South Shetland Trench. Approximately 3 million years ago spreading stopped at the Antarctic-Phoenix spreading center in

Drake Passage The Drake Passage (referred to as Mar de Hoces Hoces Sea"in Spanish-speaking countries) is the body of water between South America's Cape Horn, Chile and the South Shetland Islands of Antarctica. It connects the southwestern part of the Atla ...

. The Phoenix Plate is now considered part of the larger Antarctic Plate due to a lack of relative movement between the two since spreading ceased. However, subduction in the South Shetland Trench did not cease.

Slab rollback Oceanic trenches are prominent long, narrow topographic depressions of the ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers in length. There are about of oceanic tren ...

of the former Phoenix Plate underneath the South Shetland Islands caused rifting to develop in the Antarctic Peninsula creating the Shetland Plate and the Bransfield Basin. Rifting centers in the Bransfield Basin continue to separate the Shetland Plate from the Antarctic Peninsula.

Tectonic setting

South Shetland Trench

The South Shetland Trench forms the northwest border of the Shetland Plate. The trench is formed by the subduction of the Antarctic Plate in the north under the Shetland Plate in the south. Subduction along this trench has slowed significantly over time, from per year over the last 30 million years to per year in the last 6 million years. Current subduction is caused by the movement of the Shetland Plate northward, as well as,

slab rollback Oceanic trenches are prominent long, narrow topographic depressions of the ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers in length. There are about of oceanic tren ...

of the former Phoenix Plate.

Bransfield Basin

The Bransfield Basin forms the southeast border of the Shetland Plate. The basin separates the Shetland Plate on the north and the Antarctic Plate to the south. The basin is a

back-arc A back-arc basin is a type of geologic basin, found at some convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most o ...

rift basin. The basin ranges from to more than deep.

Fracture Zones

The Shackleton Fracture Zone is the northeast border of the Shetland Plate. The fracture zone is a series of parallel transform faults separating the

from the Shetland Plate. This border with the Scotia Plate is the only Shetland Plate boundary that is not with the Antarctic Plate. The Hero Fracture Zone is the southwest boundary of the Shetland Plate. This feature separates the Shetland Plate from the Antarctic Plate. These parallel faults connect the Bransfield Basin in the south to the South Shetland Trench in the north.

Volcanism

Absolute K-Ar ages indicate volcanism has been active from the Cenozoic to the present. Current volcanism can be seen at

Deception Island Deception Island is an island in the South Shetland Islands close to the Antarctic Peninsula with a large and usually "safe" natural harbor, which is occasionally troubled by the underlying active volcano. This island is the caldera of an acti ...

and Penguin Island. Plutons of

calc-alkaline The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic m ...

compositions, formed from a type of magma created above subduction zones, date from the Cenozoic to the

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

and is coincident with the active subduction of the Phoenix plate under Antarctica. More recent

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58mid ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a diverg ...

tholeiitic The tholeiitic magma series is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma ...

magmas. The transitional chemistry can be explained by back-arc rifting in the Bransfield Basin.

Earthquakes

Since the early 1980s,

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...

s have been recorded in the Shetland Plate. The amount of data has been limited by remoteness, severe weather, and a lack of permeant seismic stations in the area. Intermediate depth earthquakes (35–55 km) under the South Shetland Islands indicate that subduction is still occurring at the Shetland Trench.

References

{{DEFAULTSORT:Shetland Plate Tectonic plates Geology of Antarctica Geology of the Southern Ocean Geography of the South Shetland Islands