Subduction | geology | Britannica (original) (raw)
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Africa
In Africa: General considerations …the present Nile River, by subduction processes identical to those observed today. (Subduction involves the descent of the edge of one lithospheric plate beneath that of another where two such plates collide.) Read More
facies production
In metamorphic rock: Facies series For example, regions associated with subduction of oceanic material beneath either oceanic crust or continental crust are characterized by blueschist, greenschist, and eclogite facies rocks, whereas areas thought to reflect continent-continent collision are more typically distinguished by greenschist and amphibolite facies rocks (see also subduction zone) Read More
geochronology
In Devonian Period: Occurrence and distribution of Devonian deposits …there was probably easterly directed subduction in western North America during the Devonian. Relics of this process are incorporated into the Cordilleran mountain chain as discrete terranes that were accreted to the continent during or after the Devonian. The clearest evidence is from the mid-Famennian Antler orogeny, during which a… Read More
India
In India: The Himalayas of India Because of the continued subduction of the Indian peninsula against the Eurasian Plate, the Himalayas and the associated eastern ranges remain tectonically active. As a result, the mountains are still rising, and earthquakes—often accompanied by landslides—are common. Several since 1900 have been devastating, including one in 1934 in what… Read More
lithospheric plates
In Earth: The outer shell …into the asthenosphere—a process called subduction. Only the thinner, denser slabs of oceanic crust will subduct, however. When two thicker, more buoyant continents come together at convergent zones, they resist subduction and tend to buckle, producing great mountain ranges. The Himalayas, along with the adjacent Plateau of Tibet, were formed… Read More
magma
In igneous rock: Origin of magmas …crust and upper mantle) is subducted so that its edge is positioned below the edge of the continental plate or another oceanic plate. Heat will be added to the subducting lithosphere as it moves slowly into the hotter depths of the mantle. The andesitic magma is believed to be generated… Read More
North America
In Pacific mountain system: Geology Subduction (crustal sinking) is not currently occurring in these two areas. Seismic activity, particularly in California, is considerable along the transform faults. After Alaska, California is the most earthquake-prone area in North America. Read More
In plate tectonics: Plate tectonics and the geologic past …years has been obliterated by subduction. Some of the other hallmarks of subduction—such as the high-pressure low-temperature metamorphic belts and the preservation of ophiolites—are very poorly represented in orogenic belts (belts of former or actual mountain ranges resulting from crustal deformation related to subduction or continental collision) that are older… Read More
regional metamorphism
In metamorphic rock: Regional metamorphism Rapid subduction of the cool oceanic lithosphere perturbs the thermal regime in such a way that high pressures can be obtained at relatively low temperatures, thereby generating blueschists and eclogites (high-pressure facies series) from ocean-floor basalts transported down the subduction zone. Continued subduction of these rocks… Read More
South America
In South America: Early Paleozoic events …Paleozoic were partially activated by subduction of oceanic crust (i.e., the forced descent of oceanic crust beneath the leading edge of an overriding continental plate) during late Cambrian to Ordovician times (about 500 to 470 million years ago). When the oceanic crust was totally consumed, subduction ceased and a series… Read More
In Andes Mountains: Geology , the Nazca Plate was subducted), the result of the latter plate’s westward movement in response to the opening of the Atlantic Ocean to the east. This subduction-uplift process was accompanied by the intrusion of considerable quantities of magma from the mantle, first in the form of a volcanic arc… Read More
