Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with rates of convergence as high as 11 cm/year.
A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic hotspots, such as Hawaii or Iceland, and large igneous provinces such as the Deccan and Siberian Traps. Some such volcanic regions lie far from tectonic plate boundaries, while others represent unusually large-volume volcanism near plate boundaries.
A volcanic arc is a belt of volcanoes formed above a subducting oceanic tectonic plate, with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc located further from the subducting plate than the trench. The oceanic plate is saturated with water, mostly in the form of hydrous minerals such as micas, amphiboles, and serpentine minerals. As the oceanic plate is subducted, it is subjected to increasing pressure and temperature with increasing depth. The heat and pressure break down the hydrous minerals in the plate, releasing water into the overlying mantle. Volatiles such as water drastically lower the melting point of the mantle, causing some of the mantle to melt and form magma at depth under the overriding plate. The magma ascends to form an arc of volcanoes parallel to the subduction zone.
The Nazca Ridge is a submarine ridge, located on the Nazca Plate off the west coast of South America. This plate and ridge are currently subducting under the South American Plate at a convergent boundary known as the Peru-Chile Trench at approximately 7.7 cm (3.0 in) per year. The Nazca Ridge began subducting obliquely to the collision margin at 11°S, approximately 11.2 Ma, and the current subduction location is 15°S. The ridge is composed of abnormally thick basaltic ocean crust, averaging 18 ±3 km thick. This crust is buoyant, resulting in flat slab subduction under Peru. This flat slab subduction has been associated with the uplift of Pisco Basin and the cessation of Andes volcanism and the uplift of the Fitzcarrald Arch on the South American continent approximately 4 Ma.
The back-arc region is the area behind a volcanic arc. In island volcanic arcs, it consists of back-arc basins of oceanic crust with abyssal depths, which may be separated by remnant arcs, similar to island arcs. In continental arcs, the back-arc region is part of continental platform, either dry land (subaerial) or forming shallow marine basins.
In geology, the slab is a significant constituent of subduction zones.
Eclogitization is the tectonic process in which the high-pressure, metamorphic facies, eclogite, is formed. This leads to an increase in the density of regions of Earth's crust, which leads to changes in plate motion at convergent boundaries.
The South Tibetan Detachment is one of the major faults in the Himalaya Mountains.
High pressure terranes along the ~1200 km long east-west trending Bangong-Nujiang suture zone (BNS) on the Tibetan Plateau have been extensively mapped and studied. Understanding the geodynamic processes in which these terranes are created is key to understanding the development and subsequent deformation of the BNS and Eurasian deformation as a whole.
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.
Flat slab subduction is characterized by a low subduction angle beyond the seismogenic layer and a resumption of normal subduction far from the trench. A slab refers to the subducting lower plate. A broader definition of flat slab subduction includes any shallowly dipping lower plate, as in western Mexico. Flat slab subduction is associated with the pinching out of the asthenosphere, an inland migration of arc magmatism, and an eventual cessation of arc magmatism. The coupling of the flat slab to the upper plate is thought to change the style of deformation occurring on the upper plate's surface and form basement-cored uplifts like the Rocky Mountains. The flat slab also may hydrate the lower continental lithosphere and be involved in the formation of economically important ore deposits. During the subduction, a flat slab itself may deform or buckle, causing sedimentary hiatus in marine sediments on the slab. The failure of a flat slab is associated with ignimbritic volcanism and the reverse migration of arc volcanism. Multiple working hypotheses about the cause of flat slabs are subduction of thick, buoyant oceanic crust (15–20 km) and trench rollback accompanying a rapidly overriding upper plate and enhanced trench suction. The west coast of South America has two of the largest flat slab subduction zones. Flat slab subduction is occurring at 10% of subduction zones.
Subduction polarity reversal is a geologic process in which two converging plates switch roles: The over-lying plate becomes the down-going plate, and vice versa. There are two basic units which make up a subduction zone. This consists of an overriding plate and the subduction plate. Two plates move towards each other due to tectonic forces. The overriding plate will be on the top of the subducting plate. This type of tectonic interaction is found at many plate boundaries.
Earth's crustal evolution involves the formation, destruction and renewal of the rocky outer shell at that planet's surface.
The South China Craton or South China Block is one of the Precambrian continental blocks in China. It is traditionally divided into the Yangtze Block in the NW and the Cathaysia Block in the SE. The Jiangshan–Shaoxing Fault represents the suture boundary between the two sub-blocks. Recent study suggests that the South China Block possibly has one more sub-block which is named the Tolo Terrane. The oldest rocks in the South China Block occur within the Kongling Complex, which yields zircon U–Pb ages of 3.3–2.9 Ga.
Earth system interactions across mountain belts are interactions between processes occurring in the different systems or "spheres" of the Earth, as these influence and respond to each other through time. Earth system interactions involve processes occurring at the atomic to planetary scale which create linear and non-linear feedback(s) involving multiple Earth systems. This complexity makes modelling Earth system interactions difficult because it can be unclear how processes of different scales within the Earth interact to produce larger scale processes which collectively represent the dynamics of the Earth as an intricate interactive adaptive system.
The geology of Himachal Pradesh is dominated by Precambrian rocks that were assembled and deformed during the India-Asia collision and the subsequent Himalayan orogeny. The Northern Indian State Himachal Pradesh is located in the Western Himalaya. It has a rugged terrain, with elevation ranging from 320m to 6975m. Rock materials in the region are largely from the Indian craton, and their ages range from the Paleoproterozoic to the present day. It is generally agreed that the Indian craton collided with Asia 50-60 million years ago (Ma). Rock sequences were thrust and folded immensely during the collision. The area has also been shaped by focused orographic precipitation, glaciation and rapid erosion.
The plate theory is a model of volcanism that attributes all volcanic activity on Earth, even that which appears superficially to be anomalous, to the operation of plate tectonics. According to the plate theory, the principal cause of volcanism is extension of the lithosphere. Extension of the lithosphere is a function of the lithospheric stress field. The global distribution of volcanic activity at a given time reflects the contemporaneous lithospheric stress field, and changes in the spatial and temporal distribution of volcanoes reflect changes in the stress field. The main factors governing the evolution of the stress field are:
- Changes in the configuration of plate boundaries.
- Vertical motions.
- Thermal contraction.
Intraplate volcanism is volcanism that takes place away from the margins of tectonic plates. Most volcanic activity takes place on plate margins, and there is broad consensus among geologists that this activity is explained well by the theory of plate tectonics. However, the origins of volcanic activity within plates remains controversial.
Andréa Tommasi is a geoscientist from Brazil known for her research on geodynamics and terrestrial deformation. She is a recipient of the CNRS silver medal and an elected fellow of the American Geophysical Union.
Oblique subduction is a form of subduction for which the convergence direction differs from 90° to the plate boundary. Most convergent boundaries involve oblique subduction, particularly in the Ring of Fire including the Ryukyu, Aleutian, Central America and Chile subduction zones. In general, the obliquity angle is between 15° and 30°. Subduction zones with high obliquity angles include Sunda trench and Ryukyu arc.
