Plume tectonics

Plume tectonics is a geoscientific theory that finds its roots in the mantle doming concept which was especially popular during the 1930s and initially did not accept major plate movements and continental drifting. It has survived from the 1970s until today in various forms and presentations. It has slowly evolved into a concept that recognises and accepts large scale plate motions such as envisaged by plate tectonics, but placing them in a framework where large mantle plumes are the major driving force of the system[1]. The initial followers of the concept during the first half of the 20th Century are scientists like Beloussov and van Bemmelen, and recently the concept has gained interest especially in Japan, through new compiled work on palaeomagnetism, and is still advocaded by the group of scientists elaboration upon Earth expansion[2]. It is nowadays generally not accepted as the main theory to explain the driving forces of tectonic plate movements, although numerous modulations on the concept have been proposed.

The theory focuses on the movements of mantle plumes under tectonic plates, viewing them as the major driving force of movements of (parts of) the Earth's crust. In its more modern form, conceived in the 1970s, it tries to reconcile in one single geodynamic model the horizontalistic concept of Plate tectonics, and the verticalistic concepts of mantle plumes, by the gravitational movement of plates away from major domes of the Earth's crust. The existence of various supercontinents in Earth history and their break-up has been associated recently with major upwellings of the mantle.

It is classified together with mantle convection as one of the mechanism that are used to explain the movements of tectonic plates. It also shows affinity with the concept of hot spots which is used in modern day plate teconics to generate a framework of specific mantle upwelling points that are relatively stable throughout time and are used to calibrate the plate movements using their location together with paleomagnetic data. Another affinity is the concept of surge tectonics which envisage flows through the mantle as major driving forces of Plate Tectonics.

References

  1. ^ Van Bemmelen, R.W. (1976); Plate Tectonics and the Undation Model: a comparison. Tectonophysics, 32, 145-182.
  2. ^ Wezel, F.-C. (1988, Ed.); The origin and evolution of arcs. Tectonophysics, Vol. 146, No.1-4, Special Issue.
  • Maruyama, Shigenori (1994). "Plume tectonics". Journal of the Geological Society of Japan. 100: 24–49. doi:10.5575/geosoc.100.24.
  • Yuen, DA; Maruyama, S; Karato, SJ; et al., eds. (2007). Superplumes: beyond plate tectonics. AA Dordrecht, NL: Springer. ISBN 978-1-4020-5749-6.
  • Segev, A (2002). "Flood basalts, continental breakup and the dispersal of Gondwana: evidence for periodic migration of upwelling mantle flows (plumes)". EGU Stephan Mueller Special Publication Series. 2: 171–91. doi:10.5194/smsps-2-171-2002.

See also

  • Hotspot (geology) – Volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle
Kunlun Volcanic Group

Kunlun volcanic group, also known as Ashikule, is a volcanic field in northwestern Tibet. Eight other volcanic fields are also in the area. The field is within a basin that also contains three lakes.

Volcanism in the field has produced lavas and cones, with rocks having varying compositions dominated by trachyandesite. Volcanism in the field may be influenced by faults in the area.

The dates obtained from the field range from 5.0 ± 0.6 million years ago to 74,000 ± 4,000 years ago. An eruption of Ashi volcano was observed in 1951, making this one of China's youngest volcanoes.

Northern Tibet volcanic field

Northern Tibet volcanic field is a volcanic field in China.

Outline of plate tectonics

This is a list of articles related to plate tectonics and tectonic plates.

Plate tectonics

Plate tectonics (from the Late Latin tectonicus, from the Greek: τεκτονικός "pertaining to building") is a scientific theory describing the large-scale motion of seven large plates and the movements of a larger number of smaller plates of the Earth's lithosphere, since tectonic processes began on Earth between 3.3 and 3.5 billion years ago. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century. The geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s and early 1960s.

The lithosphere, which is the rigid outermost shell of a planet (the crust and upper mantle), is broken into tectonic plates. The Earth's lithosphere is composed of seven or eight major plates (depending on how they are defined) and many minor plates. Where the plates meet, their relative motion determines the type of boundary: convergent, divergent, or transform. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries (or faults). The relative movement of the plates typically ranges from zero to 100 mm annually.Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust. Along convergent boundaries, subduction, or one plate moving under another, carries the lower one down into the mantle; the material lost is roughly balanced by the formation of new (oceanic) crust along divergent margins by seafloor spreading. In this way, the total surface of the lithosphere remains the same. This prediction of plate tectonics is also referred to as the conveyor belt principle. Earlier theories, since disproven, proposed gradual shrinking (contraction) or gradual expansion of the globe.Tectonic plates are able to move because the Earth's lithosphere has greater mechanical strength than the underlying asthenosphere. Lateral density variations in the mantle result in convection; that is, the slow creeping motion of Earth's solid mantle. Plate movement is thought to be driven by a combination of the motion of the seafloor away from spreading ridges due to variations in topography (the ridge is a topographic high) and density changes in the crust (density increases as newly formed crust cools and moves away from the ridge). At subduction zones the relatively cold, dense crust is "pulled" or sinks down into the mantle over the downward convecting limb of a mantle cell. Another explanation lies in the different forces generated by tidal forces of the Sun and Moon. The relative importance of each of these factors and their relationship to each other is unclear, and still the subject of much debate.

Pressure-temperature-time path

The Pressure-Temperature-time path (P-T-t path) is a record of the pressure and temperature (P-T) conditions that a rock experienced in a metamorphic cycle from burial and heating to uplift and exhumation to the surface. Metamorphism is a dynamic process which involves the changes in minerals and textures of the pre-existing rocks (protoliths) under different P-T conditions in solid state. The changes in pressures and temperatures with time experienced by the metamorphic rocks are often investigated by petrological methods, radiometric dating techniques and thermodynamic modeling.Metamorphic minerals are unstable upon changing P-T conditions. The original minerals are commonly destroyed during solid state metamorphism and react to grow into new minerals that are relatively stable. Water is generally involved in the reaction, either from the surroundings or generated by the reaction itself. Usually, a large amount of fluids (e.g. water vapor, gas etc.) escape under increasing P-T conditions e.g. burial. When the rock is later uplifted, due to the escape of fluids at an earlier stage, there is not enough fluids to permit all the new minerals to react back into the original minerals. Hence, the minerals are not fully in equilibrium when discovered on the surface. Therefore, the mineral assemblages in metamorphic rocks implicitly record the past P-T conditions that the rock has experienced, and investigating these minerals can supply information about the past metamorphic and tectonic history.The P-T-t paths are generally classified into two types: clockwise P-T-t paths, which are related to collision origin, and involve high pressures followed by high temperatures; and anticlockwise P-T-t paths, which are usually of intrusion origin, and involve high temperatures before high pressures. (The "clockwise" and "anticlockwise" names refer to the apparent direction of the paths in the Cartesian space, where the x-axis is temperature, and the y-axis is pressure.)

Thaumasia Planum

The Thaumasia Planum of Mars lies south of Melas Chasmata and Coprates Chasmata. It is in the Coprates quadrangle. Its center is located at 21.66 S and 294.78 E. It was named after a classical albedo feature. The name was approved in 2006.

Some forms on its surface are evidence of a flow of lava or water the Melas Chasma. Many wrinkle ridges and grabens are visible. One set of grabens, called Nia Fossae, seem to follow the curve of Melas Chasmata which lies just to the north.

Some researchers have discovered dikes in this region. For the study, Thermal Emission Imaging System (THEMIS) daytime infrared images, THEMIS nighttime infrared images, CTX images, and HiRISE images were used. These dikes contain magnesium-rich olivine which indicates a primitive magma composition. Dikes occur when magma follows cracks and faults under the ground. Sometimes erosion reveals them. The presence of pit craters, narrow grabens, linear troughs, and ovoid troughs are also evidence of dikes. These dikes that lie close to and parallel to Valles Marineris, the great canyon system, are evidence that extensional stress aided the formation of Valles Marineris. They may be part of a system of dikes that came from the same magma source that fed the whole area. That source may have been a “plume” of molted rock that rose from the Martian mantle.

So, the following events happened to produce the current landscape in Thaumasia Planum.

1. The mass of the volcanoes of Tharsis caused stress that resulted in fractures.2. Basalt lava flows covered the region. The flows may have come from a system of dikes.3. Wrinkle ridges formed as a result of regional compression.4. The final stage was the covering the area with volcanic ash and dust. Wind moved the surface material around.

Timeline of the development of tectonophysics (after 1952)

The evolution of tectonophysics is closely linked to the history of the continental drift and plate tectonics hypotheses. The continental drift/ Airy-Heiskanen isostasy hypothesis had many flaws and scarce data. The fixist/ Pratt-Hayford isostasy, the contracting Earth and the expanding Earth concepts had many flaws as well.

The idea of continents with a permanent location, the geosyncline theory, the Pratt-Hayford isostasy, the extrapolation of the age of the Earth by Lord Kelvin as a black body cooling down, the contracting Earth, the Earth as a solid and crystalline body, is one school of thought. A lithosphere creeping over the asthenosphere is a logical consequence of an Earth with internal heat by radioactivity decay, the Airy-Heiskanen isostasy, thrust faults and Niskanen's mantle viscosity determinations.

Timeline of the development of tectonophysics (before 1954)

The evolution of tectonophysics is closely linked to the history of the continental drift and plate tectonics hypotheses. The continental drift/ Airy-Heiskanen isostasy hypothesis had many flaws and scarce data. The fixist/ Pratt-Hayford isostasy, the contracting Earth and the expanding Earth concepts had many flaws as well.

The idea of continents with a permanent location, the geosyncline theory, the Pratt-Hayford isostasy, the extrapolation of the age of the Earth by Lord Kelvin as a black body cooling down, the contracting Earth, the Earth as a solid and crystalline body, is one school of thought. A lithosphere creeping over the asthenosphere is a logical consequence of an Earth with internal heat by radioactivity decay, the Airy-Heiskanen isostasy, thrust faults and Niskanen's mantle viscosity determinations.

University of Tokushima

Tokushima University (徳島大学, Tokushima Daigaku) is a national university in the city of Tokushima, Japan, with seven graduate schools and five undergraduate faculties. The university was founded in 1949, by merging six national education facilities into one. The 2014 Nobel Prize Laureate in Physics, Shuji Nakamura graduated from Tokushima.

On April 1, 2015 the name of the university was changed from the University of Tokushima to Tokushima University.

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