Kula Plate

The Kula Plate was an oceanic tectonic plate under the northern Pacific Ocean south of the Near Islands segment of the Aleutian Islands. It has been subducted under the North American Plate at the Aleutian Trench, being replaced by the Pacific Plate.

The name Kula is from a Tlingit language word meaning "all gone".[1] As the name suggests, the Kula Plate was entirely subducted around 48 Ma and today only a slab in the mantle under the Bering Sea remains.[2]

North America subduction
Plate distribution 64–74 Ma

Geological history

The Kula Plate began subducting under the Pacific Northwest region of North America during the Late Cretaceous period much like the Pacific Plate does, supporting a large volcanic arc system from northern Washington to southwestern Yukon called the Coast Range Arc.

There was a triple junction of three ridges between the Kula Plate to the north, the Pacific Plate to the west and the Farallon Plate to the east. The Kula Plate was subducted under the North American Plate at a relatively steep angle, so that the Canadian Rockies are primarily composed of thrusted sedimentary sheets with relatively little contribution of continental uplift, while the American Rockies are characterized by significant continental uplift in response to the shallow subduction of the Farallon Plate.

About 55 million years ago, the Kula Plate began an even more northerly motion. Riding on the Kula Plate was the Pacific Rim Terrane consisting of volcanic and sedimentary rocks. It was scraped off and plastered against the continental margin, forming what is today Vancouver Island.

By 40 million years ago, the compressional force of the Kula Plate ceased. The existence of the Kula Plate was inferred from the westward bend in the alternating pattern of magnetic anomalies in the Pacific Plate.

See also


  1. ^ p. 145 Archived March 2, 2012, at the Wayback Machine
  2. ^ Gorbatov, A.; Widiyantoro, S.; Fukao, Y.; Gordeev, E. (2000). "Signature of remnant slabs in the North Pacific from P-wave tomography" (PDF). Geophysical Journal International. 142 (1): 27–36. Bibcode:2000GeoJI.142...27G. doi:10.1046/j.1365-246X.2000.00122.x. Retrieved 30 July 2016.

External links

Aleutian Basin

The Aleutian Basin is an oceanic basin under the southwestern Bering Sea. While the northeastern half of the Bering Sea overlies the North American Plate in relatively shallow water, the Aleutian Basin consists of oceanic plate—the remnant of the Kula Plate that was mostly subducted under the North American Plate.Subduction of the Kula Plate ceased after the creation of the Aleutian Trench to its south. What remained of the Kula Plate attached to the North American Plate. This former subduction zone is now the Beringian Margin, which now hosts sixteen submarine canyons, including Zhemchug Canyon, the world's largest.The deep-water part of the Bering Sea is separated into the Commander and Bowers basins by the submarine Shirshov Ridge and Bowers Ridge. The Commander Basin occupies the western part of the Bering Sea, with the Shirshov Ridge on its eastern border. The Shirshov Ridge extends 750 km southward from the Russian Olyutorskii Peninsula to connect with Bowers Ridge. The Bowers Ridge extends in the form of an arc over approximately 900 km from the Aleutian Islands Arc to the northwestern termination, where it meets Shirshov Ridge. This former island arc, Bowers Ridge, is a prominent semi-circular-shaped geological that meets the Aleutian arc and, together with the Aleutians, bounds Bowers Basin.

The northern part of the Shirshov Ridge formed 95 My before the present. The ridge grows younger as it goes south, with the southern part of the Shirshov Ridge formed 33 My ago (Early Oligocene). Bowers Ridge was formed 30 My before the present (Late Oligocene).

Aleutian Islands

The Aleutian Islands (; Russian: Алеутские острова; Aleut: Tanam Unangaa, literally "Land of the Aleuts", possibly from Chukchi aliat, "island"), also called the Aleut Islands or Aleutic Islands and known before 1867 as the Catherine Archipelago, are a chain of 14 large volcanic islands and 55 smaller ones belonging to both the U.S. state of Alaska and the Russian federal subject of Kamchatka Krai. They form part of the Aleutian Arc in the Northern Pacific Ocean, occupying an area of 6,821 sq mi (17,666 km2) and extending about 1,200 mi (1,900 km) westward from the Alaska Peninsula toward the Kamchatka Peninsula in Russia, and mark a dividing line between the Bering Sea to the north and the Pacific Ocean to the south. Crossing longitude 180°, at which point east and west longitude end, the archipelago contains both the westernmost part of the United States by longitude (Amatignak Island) and the easternmost by longitude (Semisopochnoi Island). The westernmost U.S. island in real terms, however, is Attu Island, west of which runs the International Date Line. While nearly all the archipelago is part of Alaska and is usually considered as being in the "Alaskan Bush", at the extreme western end, the small, geologically related Commander Islands belong to Russia.

The islands, with their 57 volcanoes, form the northernmost part of the Pacific Ring of Fire. Physiographically, they are a distinct section of the larger Pacific Border province, which in turn is part of the larger Pacific Mountain System physiographic division.

These Islands are most known for the battles and skirmishes that occurred there during the Aleutian Islands Campaign of World War II. The Japanese landings and occupations of Kiska and Attu in June 1942 were the only two invasions of the United States during that war.

Bennett Lake Volcanic Complex

The Bennett Lake Volcanic Complex (BLVC) is a huge 50-million-year-old extinct caldera complex that spans across the British Columbia-Yukon border in Canada. It is located near the western end of the West Arm of Bennett Lake. The caldera complex is surrounded by granitic rocks containing pendants.

It is located near the eastern contact of the Coast Plutonic Complex and the Whitehorse Trough. There are thick series of pyroclastic and epiclastic rocks at the caldera. Remnants of this huge caldera complex are preserved near Bennett Lake in the Coast Mountains. The complex compose the Skukum Group.

Bering Sea

The Bering Sea (Russian: Бе́рингово мо́ре, tr. Béringovo móre) is a marginal sea of the Pacific Ocean. It forms, along with the Bering Strait, the divide between the two largest landmasses on Earth: Eurasia and The Americas. It comprises a deep water basin, which then rises through a narrow slope into the shallower water above the continental shelves.

The Bering Sea is separated from the Gulf of Alaska by the Alaska Peninsula. It covers over 2,000,000 square kilometers (770,000 sq mi) and is bordered on the east and northeast by Alaska, on the west by Russian Far East and the Kamchatka Peninsula, on the south by the Alaska Peninsula and the Aleutian Islands and on the far north by the Bering Strait, which connects the Bering Sea to the Arctic Ocean's Chukchi Sea. Bristol Bay is the portion of the Bering Sea which separates the Alaska Peninsula from mainland Alaska. The Bering Sea is named for Vitus Bering, a Danish navigator in Russian service, who in 1728 was the first European to systematically explore it, sailing from the Pacific Ocean northward to the Arctic Ocean.

The Bering Sea ecosystem includes resources within the jurisdiction of the United States and Russia, as well as international waters in the middle of the sea (known as the "Donut Hole"). The interaction between currents, sea ice, and weather makes for a vigorous and productive ecosystem.

Challis Arc

The Challis Arc was an Eocene volcanic field that stretched from southwestern British Columbia through Washington to Idaho, United States. The volcanic field extended between 42 and 49 degrees north latitude and was about 1500 kilometers in length. It exhibited volcanic activity for about 10 million years. Remnants of the Challis Arc are found as granitic plutons in the North Cascades, the Okanagan Highlands and in southcentral Idaho.

It was first theorized in 1979 that the volcanic field formed as a result of subduction of the eastern block of the Kula Plate between 57 and 37 million years ago. More recent publications argue that the Challis Arc was formed by more complex tectonic interactions. One proposed model theorizes that the Farallon plate underwent subduction and imbrication beneath the North American plate to form the Challis Arc. Another model suggests that intracontinental rifting and igneous activity between the Pacific and North American plates formed the Challis arc. By definition, a volcanic arc is formed via subduction, so the Challis Arc's naming as a volcanic arc is a matter of debate among geologists. The current limited availability of historical geochemical data prevents any of the proposed theories from being confirmed or falsified, so there is still no consensus on the Challis Arc's formation.

Coast Mountains

The Coast Mountains are a major mountain range in the Pacific Coast Ranges of western North America, extending from southwestern Yukon through the Alaska Panhandle and virtually all of the Coast of British Columbia south to the Fraser River. The mountain range's name derives from its proximity to the sea coast, and it is often referred to as the Coast Range. The range includes volcanic and non-volcanic mountains and the extensive ice fields of the Pacific and Boundary Ranges, and the northern end of the volcanic system known as the Cascade Volcanoes. The Coast Mountains are part of a larger mountain system called the Pacific Coast Ranges or the Pacific Mountain System, which includes the Cascade Range, the Insular Mountains, the Olympic Mountains, the Oregon Coast Range, the California Coast Ranges, the Saint Elias Mountains and the Chugach Mountains. The Coast Mountains are also part of the American Cordillera—a Spanish term for an extensive chain of mountain ranges—that consists of an almost continuous sequence of mountain ranges that form the western backbone of North America, Central America, South America and Antarctica.

The Coast Mountains are approximately 1,600 kilometres (1,000 mi) long and average 300 kilometres (190 mi) in width. The range's southern and southeastern boundaries are surrounded by the Fraser River and the Interior Plateau while its far northwestern edge is delimited by the Kelsall and Tatshenshini Rivers at the north end of the Alaska Panhandle, beyond which are the Saint Elias Mountains, and by Champagne Pass in the Yukon Territory. Covered in dense temperate rainforest on its western exposures, the range rises to heavily glaciated peaks, including the largest temperate-latitude ice fields in the world. On its eastern flanks, the range tapers to the dry Interior Plateau and the subarctic boreal forests of the Skeena Mountains and Stikine Plateau.

The Coast Mountains are part of the Pacific Ring of Fire—the ring of volcanoes and associated mountains around the Pacific Ocean—and contain some of British Columbia's highest mountains. Mount Waddington is the highest mountain of the Coast Mountains and the highest that lies entirely within British Columbia, located northeast of the head of Knight Inlet with an elevation of 4,019 metres (13,186 ft).

Coast Range Arc

The Coast Range Arc was a large volcanic arc system, extending from northern Washington through British Columbia and the Alaska Panhandle to southwestern Yukon. The Coast Range Arc lies along the western margin of the North American Plate in the Pacific Northwest of western North America. Although taking its name from the Coast Mountains, this term is a geologic grouping rather than a geographic one, and the Coast Range Arc extended south into the High Cascades of the Cascade Range, past the Fraser River which is the northward limit of the Cascade Range proper.

The Coast Range Arc formed as a result of subduction of the Kula and pre-existing Farallon Plates. It is most famous for being the largest granitic outcropping in North America, which then it is usually referred to as the Coast Plutonic Complex or the Coast Mountains Batholith. It is a coast-parallel continental volcanic arc similar to the Andes of South America and the largest continental volcanic arc fossil in the world.

Farallon Plate

The Farallon Plate was an ancient oceanic plate that began subducting under the west coast of the North American Plate—then located in modern Utah—as Pangaea broke apart during the Jurassic period. It is named for the Farallon Islands, which are located just west of San Francisco, California.

Over time, the central part of the Farallon Plate was completely subducted under the southwestern part of the North American Plate. The remains of the Farallon Plate are the Juan de Fuca, Explorer and Gorda Plates, subducting under the northern part of the North American Plate; the Cocos Plate subducting under Central America; and the Nazca Plate subducting under the South American Plate.The Farallon Plate is also responsible for transporting old island arcs and various fragments of continental crustal material rifted off from other distant plates and accreting them to the North American Plate.

These fragments from elsewhere are called terranes (sometimes, "exotic" terranes). Much of western North America is composed of these accreted terranes.

Geology of Alaska

The geology of Alaska includes Precambrian igneous and metamorphic rocks formed in offshore terranes and added to the western margin of North America from the Paleozoic through modern times. The region was submerged for much of the Paleozoic and Mesozoic and formed extensive oil and gas reserves due to tectonic activity in the Arctic Ocean. Alaska was largely ice free during the Pleistocene, allowing humans to migrate into the Americas.

Izanagi Plate

The Izanagi Plate (named after the Shinto god Izanagi) was an ancient tectonic plate, which began subducting beneath the Okhotsk Plate 130–100 Ma years ago. The rapid plate motion of the Izanagi Plate caused north-west Japan and the outer zone of south-west Japan to drift northward. High-pressure metamorphic rocks were formed at the eastern margin of the drifting land mass in the Sanbagawa metamorphic belt, while low-pressure metamorphic rocks were formed at its western margin in the Abukuma metamorphic belt. At approximately 95 Ma, the Izanagi Plate was completely subducted and replaced by the western Pacific Plate, which also subducted in the north-western direction. Subduction-related magmatism took place near the Ryoke belt. No marked tectonics occurred in the Abunkuma belt after the change of the subducted plate.

The discovery of an extinct Jurassic–Cretaceous spreading system in the north-west Pacific led to the introduction of the extinct Kula Plate in 1972. The Izanagi Plate was subsequently introduced in 1982 to explain the geometry of this spreading system. Knowledge of the now-subducted Izanagi Plate is limited to Mesozoic magnetic lineations on the Pacific Plate that preserve the record of this subduction.

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.

Montana Mountain

Montana Mountain is a deeply eroded Late Cretaceous stratovolcano located south of Carcross, Yukon, Canada. As well as its main peak, the mountain includes many sub-peaks and contains felsic pyroclastics and flows; typically altered and orange-weathering. Montana Mountain was formed when the ancient Kula Plate was subducting under southwestern Yukon during the Late Cretaceous period.

A flurry of quartz mining activity took place on Montana Mountain starting in 1899, peaking in 1905-1906 when American mining promoter John Conrad consolidated claims on Montana Mountain and built three tramways to carry the ore back down, including a 4-mile-long one from Windy Arm on Tagish Lake to the Mountain Hero mine.Montana Mountain is also an important landmark for the Carcross/Tagish First Nations living in the area. According to legend, Montana Mountain is one of the peaks Game Mother used to hang a swing for her animal creations. On this swing each kind of animal danced and sang a different song. Following this "celebration" Game Mother gave each animal their characteristic attributes of today. In addition to its spiritual importance, the mountain was also an important source of food, medicines, and refuge.

During the early quartz mining period, an extensive network of trails were constructed on the mountain to connect the many silver claims with Carcross and/or Windy Arm. In 2005 the Carcross/Tagish First Nation took back the mountain in its land claim settlement and set out to restore some of the old trails and make them accessible for public use and enjoyment.Through a programme called "SingleTrack to Success" an extensive network of mountain bike trails have been developed on the lower slopes of Montana Mountain. Additionally, these trails have been mapped and the maps are publicly available..

Mount Skukum Volcanic Complex

The Mount Skukum Volcanic Complex is an early Eocene caldera complex, located 43 km west of Carcross and 32 km northeast of Mount Porsild in the Yukon Territory, Canada. The complex composes the Skukum Group. It is a northeast-trending complex of subaerial volcanic and volcaniclastic rocks covering 140 km2.

The Mount Skukum Volcanic Complex was formed when the ancient Kula Plate was subducting under North America during the early Eocene period.

Okhotsk-Chukotka Volcanic Belt

The Okhotsk-Chukotka Volcanic Belt (OCVB) is a Cretaceous volcanic belt in the Russian Far East region of northeast Asia.

It is found in Chukotka Autonomous Okrug and Khabarovsk Krai of northeastern Russia.

Pacific Coast Ranges

The Pacific Coast Ranges (officially gazetted as the Pacific Mountain System in the United States but referred to as the Pacific Coast Ranges), are the series of mountain ranges that stretch along the West Coast of North America from Alaska south to Northern and Central Mexico.

The Pacific Coast Ranges are part of the North American Cordillera (sometimes known as the Western Cordillera, or in Canada, as the Pacific Cordillera and/or the Canadian Cordillera), which includes the Rocky Mountains, Columbia Mountains, Interior Mountains, the Interior Plateau, Sierra Nevada Mountains, the Great Basin mountain ranges, and other ranges and various plateaus and basins.

The Pacific Coast Ranges designation, however, only applies to the Western System of the Western Cordillera, which comprises the Saint Elias Mountains, Coast Mountains, Insular Mountains, Olympic Mountains, Cascade Range, Oregon Coast Range, California Coast Ranges, Transverse Ranges, Peninsular Ranges, and the Sierra Madre Occidental.

Straight Creek Fault

The Straight Creek Fault (SCF) is the principal north-south strike-slip fault in the state of Washington, with a minimum of 90 kilometers (54 miles) of right-lateral offset, and a major geological structure in the North Cascade mountains, where it separates the pre-Cenozoic igneous and metamorphic rocks of the North Cascades on the east from the younger accreted terranes on the west. The SCF can be traced from its junction with the Olympic-Wallowa Lineament (OWL) near the town of Easton northward into British Columbia, where it joins the Fraser River Fault system; the combined system (over 570 km [340 miles] long) is known as the Fraser—Straight Creek Fault system (FSCF).No trace of the SCF has been found south of the OWL. Some geologists believe it does continue south, with all traces covered by more recent volcanic deposits. Others have speculated that it simply ends, or turns and aligns with the OWL, or has been offset elsewhere. (See discussion at Olympic-Wallowa Lineament#Straight Creek Fault.)

The SCF offsets the older NNW striking Entiat, Ross Lake, and Chewack-Pasayten faults, but not certain younger features, the period of its strike-slip activity thus being bracketed between 47 and 41 million years ago (in the Eocene epoch), just after the wedge of crust now carrying the Olympic Mountains pushed into the continental margin. It has been suggested that initiation of the SCF may be due to events on the Kula Plate.The SCF seems to be related to the Darrington—Devils Mountain Fault (DDMF), which runs due east from the southern end of Vancouver Island to the small town of Darrington, then turns nearly south to converge with the SCF near its intersection with the OWL. This bowing appears to be due to the approaching Olympic Mountains. An anomalous rock formation (the Helena—Haystack Melange) just north of Darrington has been correlated with similar rock south of Easton, suggesting considerable right-lateral strike-slip motion on the DDMF. Motion on both faults seems to have been contemporaneous; the relationship between the two is not understood.

Vancouver Island

Vancouver Island is in the northeastern Pacific Ocean. It is part of the Canadian province of British Columbia. The island is 460 kilometres (290 mi) in length, 100 kilometres (62 mi) in width at its widest point, and 32,134 km2 (12,407 sq mi) in area. It is the largest island on the West Coast of the Americas.

The southern part of Vancouver Island and some of the nearby Gulf Islands are the only parts of British Columbia or Western Canada to lie south of the 49th Parallel. This area has one of the warmest climates in Canada, and since the mid-1990s has been mild enough in a few areas to grow subtropical Mediterranean crops such as olives and lemons.Vancouver Island had a population in 2016 of 775,347. Nearly half of that population (367,770) live in the metropolitan area of Greater Victoria. Other notable cities and towns on Vancouver Island include Nanaimo, Port Alberni, Parksville, Courtenay, and Campbell River. Victoria, the capital city of British Columbia, is located on the island, but the larger city of Vancouver is not – it is on the North American mainland, across the Strait of Georgia from Nanaimo.

Vancouver Island has been the homeland to many Indigenous peoples for thousands of years. The island was explored by British and Spanish expeditions in the late 18th century. It was named Quadra's and Vancouver's Island in commemoration of the friendly negotiations held in 1792 by Spanish commander of the Nootka Sound settlement, Juan Francisco de la Bodega y Quadra, and by British naval captain George Vancouver, during the Nootka Crisis. Bodega y Quadra's name was eventually dropped from the name. It is one of several North American locations named after George Vancouver, who explored the Pacific Northwest coast between 1791 and 1794.

Vancouver Island is the world's 43rd largest island, Canada's 11th largest island, and Canada's second most populous island after the Island of Montreal. It is the largest Pacific island anywhere east of New Zealand.

Volcanology of Canada

Volcanology of Canada includes lava flows, lava plateaus, lava domes, cinder cones, stratovolcanoes, shield volcanoes, submarine volcanoes, calderas, diatremes, and maars, along with examples of more less common volcanic forms such as tuyas and subglacial mounds. It has a very complex volcanological history spanning from the Precambrian eon at least 3.11 billion years ago when this part of the North American continent began to form.Although the country's volcanic activity dates back to the Precambrian eon, volcanism continues to occur in Western and Northern Canada where it forms part of an encircling chain of volcanoes and frequent earthquakes around the Pacific Ocean called the Pacific Ring of Fire. But because volcanoes in Western and Northern Canada are in remote rugged areas and the level of volcanic activity is less frequent than with other volcanoes around the Pacific Ocean, Canada is commonly thought to occupy a gap in the Pacific Ring of Fire between the volcanoes of western United States to the south and the Aleutian volcanoes of Alaska to the north. However, the mountainous landscape of Western and Northern Canada includes more than 100 volcanoes that have been active during the past two million years and whose eruptions have claimed many lives. Volcanic activity has been responsible for many of Canada's geological and geographical features and mineralization, including the nucleus of North America called the Canadian Shield.

Volcanism has led to the formation of hundreds of volcanic areas and extensive lava formations across Canada, indicating volcanism played a major role in shaping its surface. The country's different volcano and lava types originate from different tectonic settings and types of volcanic eruptions, ranging from passive lava eruptions to violent explosive eruptions. Canada has a rich record of very large volumes of magmatic rock called large igneous provinces. They are represented by deep-level plumbing systems consisting of giant dike swarms, sill provinces and layered intrusions. The most capable large igneous provinces in Canada are Archean (3,800–2,500 million years ago) age greenstone belts containing a rare volcanic rock called komatiite.



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