The Explorer Plate is an oceanic

tectonic plate Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...

beneath the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the conti ...

off the west coast of

Vancouver Island Vancouver Island is an island in the northeastern Pacific Ocean and part of the Canadian province of British Columbia. The island is in length, in width at its widest point, and in total area, while are of land. The island is the largest by ...

, Canada, which is partially subducted under the

North American Plate The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of , it is the Earth's second largest tectonic plate, behind the Paci ...

. Along with the Juan de Fuca Plate and Gorda Plate, the Explorer Plate is a remnant of the ancient Farallon Plate, which has been subducted under the North American Plate. The Explorer Plate separated from the Juan de Fuca Plate roughly 4 million years ago. In its smoother, southern half, the average depth of the Explorer plate is roughly and rises up in its northern half to a highly variable basin between and in depth.

Boundaries

The eastern boundary of the Explorer Plate is being subducted under the North American Plate. The southern boundary is a collection of

transform fault A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subduct ...

s, the Sovanco Fracture Zone, separating the Explorer Plate from the

Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and I ...

. To the southeast is another transform boundary, the Nootka Fault, which separates the Explorer Plate from the Juan de Fuca Plate and forms a

triple junction A triple junction is the point where the boundaries of three tectonic plates meet. At the triple junction each of the three boundaries will be one of three types – a ridge (R), trench (T) or transform fault (F) – and triple junctions can b ...

with the North American Plate. To the northwest is a

divergent boundary In plate tectonics, a divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent b ...

with the Pacific Plate forming the Explorer Ridge, and the Winona Basin located within the northwest boundaries and the Pacific continental shelf. The Queen Charlotte triple junction is located where the Pacific Plate and North American Plate meets with the Explorer Plate.

Formation and evolution

Upon breaking apart 4 million years ago, the Juan De Fuca Plate continued moving northeast at 26 mm/year (1 in/year) while the Explorer Plate's velocity changed, stalling or moving slowly north up to 20 mm/year. The Nootka Fault boundary between the Juan De Fuca Plate and the Explorer Plate has varied in length and direction since their separation. The formation of the Nookta Fault and the

shearing Sheep shearing is the process by which the woollen fleece of a sheep is cut off. The person who removes the sheep's wool is called a '' shearer''. Typically each adult sheep is shorn once each year (a sheep may be said to have been "shorn" o ...

of plate boundaries has caused a clockwise rotation, reorienting the Sovanco Fracture Zone northwards along the North American Plate and slowing the Explorer Plate's subduction. The Sovanco Fracture Zone originated as a

spreading center 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 diver ...

offset more than 7 million years ago which shows southward movement from the influence of the Explorer ridge and results in uneven spreading eastward unto the Explorer Plate.

Current state of subduction

The subducted portion of the plate extends downward to more than 300 km (186 mi) depth, and laterally as far as mainland Canada. The relative

buoyancy Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the ...

of the subducting plate and the underlying mantle may be inhibiting the Explorer Plate's ability to descend further into the mantle. There is an ongoing debate regarding the process of subduction of the Explorer Plate and how the boundary between the Explorer plate and the North American Plate are defined: # The Explorer Plate has stopped and may eventually accrete, fusing with the North American plate as the subduction has fully stopped and will eventually become a plate boundary between the North American Plate and Pacific Plate rather than continuing its subduction. # The Explorer Plate consists of two parts with half being fused to the North American Plate and the other half remaining a microplate system. # The Explorer Plate has slowed to a terminal speed of 20 mm/year, and will continue until the entire plate is subducted.

Seismic activity

As a part of the

Pacific Ring of Fire The Ring of Fire (also known as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) is a region around much of the rim of the Pacific Ocean where many volcanic eruptions and earthquakes occur. The Ring ...

, the Explorer Plate has a high level of seismic activity. However, the activity consists of low-magnitude events; no earthquake above magnitude 6.5 has been recorded in the region, though a swarm of several dozen magnitude 5–6 earthquakes occurred just north of the

Seminole Seamount The Seminole Seamount is a seamount located in the Pacific Ocean off the coast of northern Vancouver Island, British Columbia, Canada. See also *Volcanism of Canada *Volcanism of Western Canada *List of volcanoes in Canada List of volcanoes ...

in 2008. The Explorer Plate is the most seismically active area of Canada, but is anomalous as a subduction zone since most of the seismic activity occurs around the plate's perimeter rather than at the subduction interface. Events are generally centered around the southern and north-western areas where the borders of the plate are in contact with other plates; however, the newer ocean crust created at Explorer ridge and Juan de Fuca ridge reduces the rigidity of the region and contributes to the low magnitude of events in the region.

References

External links

Cascadia tectonic history
{{tectonic plates Tectonic plates Geology of British Columbia Geology of the Pacific Ocean Oceanography of Canada