Wrangellia Terrane
Encyclopedia
The Wrangellia Terrane is a geologic concept encompassing a large arc of terrain
extending from the U.S state of southcentral Alaska
through southwestern Yukon
and along the Coast of British Columbia
in Canada
. Although not generally accepted, some workers contend that Wrangellia extends southward to Oregon
.
The term Wrangellia is confusingly applied to all of: the Wrangell(ia) Terrane alone; a composite terrane
(CT) consisting of the Wrangell Terrane, Peninsular Terrane, and other rock units that were not originally part of the North American craton; and a composite terrane which also includes the Alexander Terrane. Earlier workers sometimes used the term, "Talkeetna Superterrane," to describe Wrangellia.
Rocks of Wrangellia (the individual terrane, not the CT) were originally created in the Pennsylvanian
to the Jurassic
somewhere, but probably near the equator, in the Panthalassic Ocean off of the west coast of the North American craton as island arc
s, oceanic plateau
s, and rock assemblages of the associated tectonic settings. Although composed of many different rocks types, of various composition, age, and tectonic affinity, it is the late Triassic
flood basalt
s that are the defining unit of Wrangellia. These basalt
s, extruded onto land over 5-million years about 230 million years ago, on top of an extinct Pennsylvanian and Permian
island arc, constitute a large igneous province
, currently exposed in a 2500 km (1,553 mi) long belt.
Wrangellia collided and amalgamated with the Alexander Terrane by Pennsylvanian time. By the end of the Triassic Period, the Peninsular Terrane had also joined the Wrangellia CT. A subduction zone existed on the west side of Wrangellia. Seafloor rocks too light to be subducted were instead compressed againgst the western edge of Wrangellia; these rocks are now known as the Chugach Terrane. A complex fault system, known as the Border Ranges Fault, is the modern expression of the suture zone between Wrangellia and Chugach Terranes. Over time, plate tectonics
moved this amalagamation of crust generally northeastward into contact with the North American continental margin. The Wrangellia CT collided with and docked to North America by Cretaceous
time. Strike-slip displacement, with Wrangellia travelling northward, continued after docking, although the amount of post-accretion
displacement is controversial.
Terrain
Terrain, or land relief, is the vertical and horizontal dimension of land surface. When relief is described underwater, the term bathymetry is used...
extending from the U.S state of southcentral Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
through southwestern Yukon
Yukon
Yukon is the westernmost and smallest of Canada's three federal territories. It was named after the Yukon River. The word Yukon means "Great River" in Gwich’in....
and along the Coast of British Columbia
British Columbia Coast
The British Columbia Coast or BC Coast is Canada's western continental coastline on the Pacific Ocean. The usage is synonymous with the term West Coast of Canada....
in Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. Although not generally accepted, some workers contend that Wrangellia extends southward to Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
.
The term Wrangellia is confusingly applied to all of: the Wrangell(ia) Terrane alone; a composite terrane
Terrane
A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...
(CT) consisting of the Wrangell Terrane, Peninsular Terrane, and other rock units that were not originally part of the North American craton; and a composite terrane which also includes the Alexander Terrane. Earlier workers sometimes used the term, "Talkeetna Superterrane," to describe Wrangellia.
Rocks of Wrangellia (the individual terrane, not the CT) were originally created in the Pennsylvanian
Pennsylvanian
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...
to the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
somewhere, but probably near the equator, in the Panthalassic Ocean off of the west coast of the North American craton as island arc
Island arc
An island arc is a type of archipelago composed of a chain of volcanoes which alignment is arc-shaped, and which are situated parallel and close to a boundary between two converging tectonic plates....
s, oceanic plateau
Oceanic plateau
An oceanic plateau is a large, relatively flat submarine region that rises well above the level of the ambient seabed. While many oceanic plateaus are composed of continental crust, and often form a step interrupting the continental slope, some plateaus are undersea remnants of large igneous...
s, and rock assemblages of the associated tectonic settings. Although composed of many different rocks types, of various composition, age, and tectonic affinity, it is the late Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
flood basalt
Flood basalt
A flood basalt or trap basalt is the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava. Flood basalts have occurred on continental scales in prehistory, creating great plateaus and mountain ranges...
s that are the defining unit of Wrangellia. These basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
s, extruded onto land over 5-million years about 230 million years ago, on top of an extinct Pennsylvanian and Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
island arc, constitute a large igneous province
Large igneous province
A Large Igneous Province is an extremely large accumulation of igneous rocks—intrusive, extrusive, or both—in the earth's crust...
, currently exposed in a 2500 km (1,553 mi) long belt.
Wrangellia collided and amalgamated with the Alexander Terrane by Pennsylvanian time. By the end of the Triassic Period, the Peninsular Terrane had also joined the Wrangellia CT. A subduction zone existed on the west side of Wrangellia. Seafloor rocks too light to be subducted were instead compressed againgst the western edge of Wrangellia; these rocks are now known as the Chugach Terrane. A complex fault system, known as the Border Ranges Fault, is the modern expression of the suture zone between Wrangellia and Chugach Terranes. Over time, plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
moved this amalagamation of crust generally northeastward into contact with the North American continental margin. The Wrangellia CT collided with and docked to North America by Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
time. Strike-slip displacement, with Wrangellia travelling northward, continued after docking, although the amount of post-accretion
Accretion (geology)
Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features.-Description:...
displacement is controversial.
See also
- Volcanism of Canada
- Volcanism of Northern CanadaVolcanism of Northern CanadaVolcanism of Northern Canada has led to the formation of hundreds of volcanic areas and extensive lava formations across Northern Canada, indicating volcanism played a major role in shaping its surface...
- Volcanism of Western CanadaVolcanism of Western CanadaVolcanism of Western Canada produces 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.-Volcanic belts:*Anahim...
- Oceanic plateauOceanic plateauAn oceanic plateau is a large, relatively flat submarine region that rises well above the level of the ambient seabed. While many oceanic plateaus are composed of continental crust, and often form a step interrupting the continental slope, some plateaus are undersea remnants of large igneous...