What is a geological terrane?
Accreted terranes are the blocks of continental fragments and oceanic islands that have collided with a continent and are now permanently attached. All continents, including North America, tend to be older in their interiors and grow outward over geologic time, as terranes are added to the edges of the continent.
Why are terranes added to continental margins rather than subducting under them?
Why are terranes added to continental margins, rather than subducting under them? Terranes are too buoyant to subduct. The margins of many continents have grown through the accretion of terranes.
What defines the boundary of an accreted terrane?
A terrane has a geological history, as recorded in its stratigraphy, which is different from the geologic history of rocks adjacent to the terrane. A terrane is bounded, separated from the geologic surroundings into which it was accreted, by faults, which result from the tectonic processes leading to the accretion.
What is the location of the Quesnellia terrane?
Quesnellia, or the Quesnel terrane, is a terrane in British Columbia, Canada; constituent of the Canadian Cordillera. It formed volcanic arc during the Mesozoic era, in the Triassic and Jurassic periods.
What is the crust type of the Methow terrane?
oceanic crust
What is the Kootenay Arc?
The Kootenay arc is an arcuate belt of de- formed and metamorphosed rocks that extends from east-central Washington to southeastern British Columbia (Fig. 1).
What two plates collided to form the Kootenay Arc?
1) Okanogan continent is on the ocean plate & collides with the coast of North America as plate slides under continent. 3) The pressure builds, forcing the ocean plate to break behind the micro- continent, forming a new trench.
What type of rocks make up the Kootenay terrane?
Quartzites, grits, mafic volcanic rocks, and minor lenses of light-colored marble are found locally in the upper part of the Index Formation. Facing directions reported by Read and Wheeler (1976) and Klepacki and Wheeler (1985) confirm the stratigraphic order in- ferred by Fyles and Eastwood (1962).
What type of rocks make up the Cache Creek terrane in this area and how old are they?
The Cache Creek Terrane consists of Carboniferous to Lower Jurassic volcanic rocks, carbonate rocks, coarse clastic rocks and small amounts of ultramafic rock, chert and argillite.
What is a terrane?
1 : the area or surface over which a particular rock or group of rocks is prevalent.
How is a terrane formed?
In geology, a terrane (in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or “sutured” to crust lying on another plate. A sedimentary deposit that buries the contact of the terrane with adjacent rock is called an overlap formation.
What is an exotic terrane?
An exotic terrane (not “terrain”) is a piece of the Earth’s crust that has merged with another landmass that usually has a separate and entirely different geologic history.
What are the types of terrane?
The two most likely types of terranes are sections oceanic crust and entire island arcs. Also likely are oceanic plateaus (broad zones of thick oceanic crust in shallow water), ocean islands (such as the islands of Hawaii), and groups of island arcs that have already merged together.
Do terranes include Microcontinents?
Accreted Terranes Nearly all of the rock is oceanic in origin, but continental masses (microcontinents) that include transported plutonic rocks are also present. Dozens of distinct terranes were accreted at different times during Appalachian and Cordilleran orogeny.
What do you think is the reason that there are large faults in places where terranes meet?
What do you think is the reason that there are large faults in places where terranes meet? When a terrane is scraped off a sinking plate, it is put under a lot of pressure. The pressure makes the rock crack. You just studied 14 terms!
How does accretion occur?
Accretion is the process in which material from the outer plate and trench (during the periods of discontinuous subduction) is removed and added to the outer continental margin or by other mechanisms such as imbricate thrusting or a combination of folding and thrusting (Karig, 1974; Karig and Sherman, 1975).
What does Craton mean?
Craton, the stable interior portion of a continent characteristically composed of ancient crystalline basement rock. The term craton is used to distinguish such regions from mobile geosynclinal troughs, which are linear belts of sediment accumulations subject to subsidence (i.e., downwarping).
What is a Craton and why is it important?
Cratons are pieces of continents that have been stable for a over a billion years. Economically they are very important – most of the world’s diamonds come from cratonic areas as do many other valuable deposits. Cratons are stable because they are strong.
Where is the Kaapvaal Craton?
South Africa
How do cratons form quizlet?
Cratons can be described as shields, in which the basement rock crops out at the surface, and platforms, in which the basement is overlaid by sediments and sedimentary rock. Platforms, shields and the basement rocks together constitute cratons.
What is a craton group of answer choices?
A craton (kratos; Greek for strength) is an old and stable part of the continental crust that has survived the merging and splitting of continents and supercontinents for at least 500 million years. Some are over 2 billion years old. Cratons are subdivided geographically into geologic provinces.
What happened to any oxygen produced during the Archean?
During the Archean Eon, methane droplets in the air shrouded the young Earth in a global haze. There was no oxygen gas on Earth. Oxygen was only in compounds such as water. Complex chemical reactions in the young oceans transformed carbon-containing molecules into simple, living cells that did not need oxygen to live.
What was the original biological source of oxygen gas on Earth?
The answer is tiny organisms known as cyanobacteria, or blue-green algae. These microbes conduct photosynthesis: using sunshine, water and carbon dioxide to produce carbohydrates and, yes, oxygen.