Explorer Plate

The Explorer Plate is an oceanic tectonic plate beneath the Pacific Ocean off the west coast of Vancouver Island, Canada and is partially subducted under the North American Plate. 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.[3] In its smoother, southern half, the average depth of the Explorer plate is roughly 2,400 metres (7,900 ft) and rises up in its northern half to a highly variable basin between 1,400 metres (4,600 ft) and 2,200 metres (7,200 ft) in depth.

Explorer Plate
The Explorer Plate
TypeMicroplate
Coordinates49°30′N 129°30′W / 49.5°N 129.5°W
Approximate area18,000 km2 (6950 sq mi)[1]
Movement1north-east
Speed1Up to 20 mm/year [2]
FeaturesPacific Ocean
1Relative to the African Plate

Boundaries

Explorer Ridge map
Bathymetric profile of Explorer Ridge region
ExplorerPlateBathymetry
A Bathymetric Profile of the Explorer Plate Region.

The eastern boundary of the Explorer Plate is being subducted under the North American Plate. The southern boundary is a collection of transform faults, the Sovanco Fracture Zone, separating the Explorer Plate from the Pacific Plate. 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 with the North American Plate. To the northwest is a divergent boundary 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.[4] The formation of the Nookta Fault and the shearing 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.[5] The Sovanco Fracture Zone originated as a spreading center 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.[5]

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.[6] The relative buoyancy of the subducting plate and the underlying mantle may be inhibiting the Explorer Plate's ability to descend further into the mantle.[7]

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:

  1. 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.[8][3]
  2. The Explorer Plate consists of two parts with half being fused to the North American Plate and the other half remaining a microplate system.[9][10]
  3. The Explorer Plate has slowed to a terminal speed of 20 mm/year, and will continue until the entire plate is subducted.[5]

Seismic activity

As a part of the Pacific Ring of Fire, 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 in 2008.[11] 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.[8] 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.[12]

See also

References

  1. ^ "Sizes of Tectonic or Lithospheric Plates". Geology.about.com. 2014-03-05. Retrieved 2017-04-05.
  2. ^ Riddihough, Robin (1984-08-10). "Recent movements of the Juan de Fuca Plate System". Journal of Geophysical Research: Solid Earth. 89 (B8): 6980–6994. Bibcode:1984JGR....89.6980R. doi:10.1029/JB089iB08p06980. ISSN 2156-2202.
  3. ^ a b Frank, Dave. "USGS Geology and Geophysics". geomaps.wr.usgs.gov. Retrieved 2017-05-08.
  4. ^ Hyndman, R. D.; Riddihough, R. P.; Herzer, R. (1979-09-01). "The Nootka Fault Zone — a new plate boundary off western Canada". Geophysical Journal International. 58 (3): 667–683. Bibcode:1979GeoJ...58..667H. doi:10.1111/j.1365-246X.1979.tb04801.x. ISSN 0956-540X.
  5. ^ a b c Braunmiller, Jochen; Nábělek, John (2002-10-01). "Seismotectonics of the Explorer region". Journal of Geophysical Research: Solid Earth. 107 (B10): 2208. Bibcode:2002JGRB..107.2208B. doi:10.1029/2001JB000220. ISSN 2156-2202.
  6. ^ Audet, P.; Bostock, M. G.; Mercier, J.-P.; Cassidy, J. F. (2008). "Morphology of the Explorer–Juan de Fuca slab edge in northern Cascadia: Imaging plate capture at a ridge-trench-transform triple junction". Geology. 36 (11): 895. Bibcode:2008Geo....36..895A. doi:10.1130/g25356a.1.
  7. ^ Govers, Rob; Meijer, Paul Th (2001-07-15). "On the dynamics of the Juan de Fuca plate". Earth and Planetary Science Letters. 189 (3–4): 115–131. Bibcode:2001E&PSL.189..115G. doi:10.1016/S0012-821X(01)00360-0.
  8. ^ a b "Science : Canada's cracking plate feels the Earth move". New Scientist. Retrieved 2017-05-08.
  9. ^ Rohr, Kristin M. M.; Furlong, Kevin P. (1995-11-01). "Ephemeral plate tectonics at the Queen Charlotte triple junction". Geology. 23 (11): 1035–1038. doi:10.1130/0091-7613(1995)023<1035:EPTATQ>2.3.CO;2. ISSN 0091-7613.
  10. ^ Kreemer, Corné; Govers, Rob; Furlong, Kevin P.; Holt, William E. (1998-08-15). "Plate boundary deformation between the Pacific and North America in the Explorer region". Tectonophysics. 293 (3–4): 225–238. Bibcode:1998Tectp.293..225K. CiteSeerX 10.1.1.180.2770. doi:10.1016/S0040-1951(98)00089-4.
  11. ^ "Seismic Explorer". Concord Consortium. October 6, 2016. Retrieved May 25, 2017.
  12. ^ Fuis, Gary S. (1998). "West margin of North America — a synthesis of recent seismic transects". Tectonophysics. 288 (1–4): 265–292. Bibcode:1998Tectp.288..265F. doi:10.1016/s0040-1951(97)00300-4.

External links

1918 Vancouver Island earthquake

The 1918 Vancouver Island earthquake occurred in British Columbia, Canada at 12:41 a.m. Pacific Standard Time on December 6.

The earthquake was most likely of the strike-slip type, and was estimated to have a maximum perceived intensity of VII (Very strong) on the Mercalli intensity scale. The epicenter was located east of the Stewardson inlet on the west coast of Vancouver Island, with damage occurring at the Estevan Point lighthouse on the Hesquiat Peninsula. The event registered 7.2 on the moment magnitude scale and was felt as far as northern Washington state and the interior of British Columbia.

The earthquake took place in the vicinity of the Cascadia subduction zone where the Juan de Fuca Plate and the Explorer Plate are being subducted under the North American Plate at a rate of 4 centimeters (1.6 in) and less than 2 centimeters (0.79 in) per year respectively, but the event was a crustal intraplate earthquake and was produced from the complicated interaction between the plates in the area. The source of the earthquake was the Nootka transform fault, which separates the Juan de Fuca and Explorer plates and has been the origin of at least five additional moderate to large events since 1918.

Cascadia subduction zone

The Cascadia subduction zone (also referred to as the Cascadia fault, or Cascadia) is a convergent plate boundary that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is a very long, sloping subduction zone where the Explorer, Juan de Fuca, and Gorda plates move to the east and slide below the much larger mostly continental North American Plate. The zone varies in width and lies offshore beginning near Cape Mendocino Northern California, passing through Oregon and Washington, and terminating at about Vancouver Island in British Columbia.The Explorer, Juan de Fuca, and Gorda plates are some of the remnants of the vast ancient Farallon Plate which is now mostly subducted under the North American Plate. The North American Plate itself is moving slowly in a generally southwest direction, sliding over the smaller plates as well as the huge oceanic Pacific Plate (which is moving in a northwest direction) in other locations such as the San Andreas Fault in central and southern California.

Tectonic processes active in the Cascadia subduction zone region include accretion, subduction, deep earthquakes, and active volcanism of the Cascades. This volcanism has included such notable eruptions as Mount Mazama (Crater Lake) about 7,500 years ago, the Mount Meager massif (Bridge River Vent) about 2,350 years ago, and Mount St. Helens in 1980. Major cities affected by a disturbance in this subduction zone include Vancouver and Victoria, British Columbia; Seattle, Washington; and Portland, Oregon.

Continental arc

A continental arc is a type of volcanic arc occurring as an "arc-shape" topographic high region along a continental margin. The continental arc is formed at an active continental margin where two tectonic plates meet, and where one plate has continental crust and the other oceanic crust along the line of plate convergence, and a subduction zone develops. The magmatism and petrogenesis of continental crust are complicated: in essence, continental arcs reflect a mixture of oceanic crust materials, mantle wedge and continental crust materials.

Explorer Ridge

The Explorer Ridge is a mid-ocean ridge, a divergent tectonic plate boundary located about 241 km (150 mi) west of Vancouver Island, British Columbia, Canada. It lies at the northern extremity of the Pacific spreading axis. To its east is the Explorer Plate, which together with the Juan de Fuca Plate and the Gorda Plate to its south, is what remains of the once-vast Farallon Plate which has been largely subducted under the North American Plate. The Explorer Ridge consists of one major segment, the Southern Explorer Ridge, and several smaller segments. It runs northward from the Sovanco Fracture Zone to the Queen Charlotte Triple Junction, a point where it meets the Queen Charlotte Fault and the northern Cascadia subduction zone.

Geology

Geology (from the Ancient Greek γῆ, gē ("earth") and -λoγία, -logia, ("study of", "discourse")) is an earth science concerned with the solid Earth, the rocks of which it is composed, and the processes by which they change over time. Geology can also include the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology significantly overlaps all other earth sciences, including hydrology and the atmospheric sciences, and so is treated as one major aspect of integrated earth system science and planetary science.

Geology describes the structure of the Earth on and beneath its surface, and the processes that have shaped that structure. It also provides tools to determine the relative and absolute ages of rocks found in a given location, and also to describe the histories of those rocks. By combining these tools, geologists are able to chronicle the geological history of the Earth as a whole, and also to demonstrate the age of the Earth. Geology provides the primary evidence for plate tectonics, the evolutionary history of life, and the Earth's past climates.

Geologists use a wide variety of methods to understand the Earth's structure and evolution, including field work, rock description, geophysical techniques, chemical analysis, physical experiments, and numerical modelling. In practical terms, geology is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources, understanding of natural hazards, the remediation of environmental problems, and providing insights into past climate change. Geology is a major academic discipline, and it plays an important role in geotechnical engineering.

Geology of the Pacific Northwest

The geology of the Pacific Northwest includes the composition (including rock, minerals, and soils), structure, physical properties and the processes that shape the Pacific Northwest region of the United States and Canada. The region is part of the Ring of Fire: the subduction of the Pacific and Farallon Plates under the North American Plate is responsible for many of the area's scenic features as well as some of its hazards, such as volcanoes, earthquakes, and landslides.

The geology of the Pacific Northwest is vast and complex. Most of the region began forming about 200 million years ago as the North American Plate started to drift westward during the rifting of Pangaea. Since that date, the western edge of North America has grown westward as a succession of island arcs and assorted ocean-floor rocks have been added along the continental margin.

There are at least five geologic provinces in the area: the Cascade Volcanoes, the Columbia Plateau, the North Cascades, the Coast Mountains, and the Insular Mountains. The Cascade Volcanoes are an active volcanic region along the western side of the Pacific Northwest. The Columbia Plateau is a region of subdued geography that is inland of the Cascade Volcanoes, and the North Cascades are a mountainous region in the northwest corner of the United States, extending into British Columbia. The Coast Mountains and Insular Mountains are a strip of mountains along the coast of British Columbia, each with its own geological history.

Geology of the United States

The richly textured landscape of the United States is a product of the dueling forces of plate tectonics, weathering and erosion. Over the 4.5 billion-year history of our Earth, tectonic upheavals and colliding plates have raised great mountain ranges while the forces of erosion and weathering worked to tear them down. Even after many millions of years, records of Earth's great upheavals remain imprinted as textural variations and surface patterns that define distinctive landscapes or provinces.The diversity of the landscapes of the United States can be easily seen on the shaded relief image to the right. The stark contrast between the ‘rough' texture of the western US and the ‘smooth' central and eastern regions is immediately apparent. Differences in roughness (topographic relief) result from a variety of processes acting on the underlying rock. The plate tectonic history of a region strongly influences the rock type and structure exposed at the surface, but differing rates of erosion that accompany changing climates can also have profound impacts on the land.There are twelve main geological provinces in the United States: Pacific, Columbia Plateau, Basin and Range, Colorado Plateau, Rocky Mountains, Laurentian Upland, Interior Plains, Interior Highlands, Appalachian Highlands, Atlantic Plain, Alaskan, and Hawaiian. Each province has its own geologic history and unique features. This article will describe each province in turn.

Ghost forest

Ghost forests are areas of dead trees in former forests, typically in coastal regions where rising sea levels or tectonic shifts have altered the height of a land mass. Forests located near the coast or estuaries may also be at risk of dying through saltwater poisoning, if invading seawater reduces the amount of freshwater that deciduous trees receive for sustenance.Looking at the stratigraphic record, it is possible to reconstruct a series of events that lead to the creation of a ghost forest. Where, in a convergent plate boundary, there has been orogenic uplift, followed by earthquakes resulting in subsidence and tsunamis, altering the coast and creating a ghost forest.

Haddington Island (British Columbia)

Haddington Island (French: île Haddington) is a small volcanic island in the Canadian province of British Columbia, located south of Malcolm Island and Broughton Strait. It is located in the Mount Waddington Regional District.

The closest major community to Haddington Island is Port McNeill.

Juan de Fuca Plate

The Juan de Fuca Plate is a tectonic plate generated from the Juan de Fuca Ridge that is subducting under the northerly portion of the western side of the North American Plate at the Cascadia subduction zone. It is named after the explorer of the same name. One of the smallest of Earth's tectonic plates, the Juan de Fuca Plate is a remnant part of the once-vast Farallon Plate, which is now largely subducted underneath the North American Plate.

List of tectonic plates

This is a list of tectonic plates on the Earth's surface. Tectonic plates are pieces of Earth's crust and uppermost mantle, together referred to as the lithosphere. The plates are around 100 km (62 mi) thick and consist of two principal types of material: oceanic crust (also called sima from silicon and magnesium) and continental crust (sial from silicon and aluminium). The composition of the two types of crust differs markedly, with mafic basaltic rocks dominating oceanic crust, while continental crust consists principally of lower-density felsic granitic rocks.

Mount Cayley massif

The Mount Cayley massif is a group of mountains in the Pacific Ranges of southwestern British Columbia, Canada. Located 45 km (28 mi) north of Squamish and 24 km (15 mi) west of Whistler, the massif resides on the edge of the Powder Mountain Icefield. It consists of an eroded but potentially active stratovolcano that towers over the Cheakamus and Squamish river valleys. All major summits have elevations greater than 2,000 m (6,600 ft), Mount Cayley being the highest at 2,385 m (7,825 ft). The surrounding area has been inhabited by indigenous peoples for more than 7,000 years while geothermal exploration has taken place there for the last four decades.

Part of the Garibaldi Volcanic Belt, the Mount Cayley massif was formed by subduction zone volcanism along the western margin of North America. Eruptive activity began about 4,000,000 years ago and has since undergone three stages of growth, the first two of which built most of the massif. The latest eruptive period occurred sometime in the last 400,000 years with lesser activity continuing into the present day.

Future eruptions are likely to threaten neighbouring communities with pyroclastic flows, lahars (volcanically induced mudslides, landslides and debris flows) and floods. To monitor this threat, the volcano and its surroundings are monitored by the Geological Survey of Canada (GSC). Eruption impact would be largely a result of the concentration of vulnerable infrastructure in nearby valleys.

Nootka Fault

The Nootka Fault is an active transform fault running southwest from Nootka Island, near Vancouver Island, British Columbia, Canada.

Outline of plate tectonics

This is a list of articles related to plate tectonics and tectonic plates.

Pacific Plate

The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres (40,000,000 sq mi), it is the largest tectonic plate.The Pacific Plate contains an interior hot spot forming the Hawaiian Islands.Hillis and Müller are reported to consider the Bird's Head Plate to be moving in unison with the Pacific Plate. Bird considers them to be unconnected.

Queen Charlotte Triple Junction

The Queen Charlotte Triple Junction is a geologic triple junction where three tectonic plates meet: the Pacific Plate, the North American Plate, and the Explorer Plate. The three plate boundaries which intersect here are the Queen Charlotte Fault, the northern Cascadia subduction zone, and the Explorer Ridge. The Queen Charlotte triple junction is currently positioned adjacent to the Queen Charlotte Sound near the Dellwood Knolls off the coast of Vancouver Island. 10 Ma to 1.5 Ma prior to the triple junction's current location, it was located southwest of Vancouver Island The movements of the triple junction have been characterized by two major shifts in the Pacific-North American Tertiary plate tectonic record. First, at approximately 40 Ma the relative plate motions switched from orthogonal convergence to right-lateral strike slip. The variance in location of the triple junction may have also been related to the formation of an independent basin block. This formation could have been produced by fore-arc bending of the Pacific Plate, due to oblique underthrusting prior to 1 Ma which produced stresses sufficient to break the Pacific Plate and isolate the block. Transpression of 15–30 mm/yr since 5 Ma has been taking place, as well as varying amounts of both transpression and transtension occurring before then. To the northwest of the triple junction the Pacific plate currently has 15 degrees of oblique convergence, passing under the North American plate along the Queen Charlotte transform fault zone. The Explorer plate is a small chunk of the Juan de Fuca plate that broke away from the Juan de Fuca Plate about 3.5 Ma and has moved much slower with respect to North America.

Sovanco Fracture Zone

The Sovanco Fracture Zone is a right lateral-moving transform fault and associated fracture zone located offshore of Vancouver Island in Canada. It runs between the northern end of the Juan de Fuca Ridge and the southern end of the Explorer Ridge, forming part of the boundary between the Pacific Plate and the Explorer Plate. To its west lies the Explorer Seamount.

The Table

The Table, sometimes called Table Mountain, is a 2,021-metre (6,631 ft) high flow-dominated andesite tuya located 4 kilometres (2 mi) south of Garibaldi Lake, 15 kilometres (9 mi) northeast of Cheekye and 5 kilometres (3 mi) north of Mount Garibaldi, British Columbia, Canada. It rises over 530 metres (1,740 ft) above the surface of Garibaldi Lake, which lies less than 1 kilometre (1 mi) to the north.

The Table is almost impossible to climb because sections of the volcano have collapsed, creating steep and exceptionally rotten rock walls on all sides.

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 3 types - a ridge (R), trench (T) or transform fault (F) - and triple junctions can be described according to the types of plate margin that meet at them (e.g. Transform-Transform-Trench, Ridge-Ridge-Ridge, or abbreviated F-F-T, R-R-R). Of the many possible types of triple junction only a few are stable through time ('stable' in this context means that the geometrical configuration of the triple junction will not change through geologic time). The meeting of 4 or more plates is also theoretically possible but junctions will only exist instantaneously.

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