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Geophysical and Petrological Modeling of the Structure and Composition of the Mantle. Pyrolite.
The structure and composition of the crust and upper
mantle depend on the geological history.
Understanding the structure of the lithosphere–asthenosphere
system is fundamental for gaining a better
insight into several processes, including volcanism and
seismicity. Information on the properties of
the upper mantle and lower crust can be gained by geophysical
investigations. Seismicwave velocities and gravimetric
data are extensively used to investigate crustal and
mantle structure.
Equally important information can be obtained from
petrological and geochemical studies of magmas and of
high-pressure xenoliths entrained in volcanic rocks.
Magmas are generated at various depths, from middle–
upper crust to the asthenosphere, and are important
potential carrier of information on the composition of
the entire LAS.
Combined petrological, geochemical and geophysical
studies are particularly useful in complex areas
where young and compositionally variable magmatism
occurs.
Pyrolite is a theoretical rock considered to be the best approximation of the composition of Earth's upper mantle. The definition varies, but it is generally considered as being about one part tholeiitic basalt and three parts peridotite. The relative abundances of the principal metallic element components (except iron) are similar to those in chondritic meteorites and in the solar photosphere. Accordingly, it is reasonable to assume that to a first approximation these abundances are applicable to the entire mantle. If fused experimentally, this mix yields high pressure tholeiitic basaltic melts, and intermediate pressure alkaline basalts. The hypothetical pyrolite compositions are not compatible with trace element, isotopic and chondritic abundances data as well as evidence for mantle heterogeneity
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Upper Mantle and Lithosphere Dynamics
The lithosphere features many of Earth's active processes such as the formation of mountain belts, subduction of oceanic lithosphere into the mantle underneath, rifting of continents, the formation of passive margins and the evolution of sedimentary basins.
An understanding of the dynamic evolution of these processes is of prime importance for understanding the hazards related to them (volcanism, land slides and earthquakes) and for research into petroleum occurrences.
Plate reconstructions document the movement of continents and the creation and destruction of oceanic plates. On a large scale, lithosphere movements provide a driving force for mantle flow through subduction and gravitational spreading at mid-ocean ridges. In turn, dynamic flow of the mantle drives lithosphere deformation. On a more regional scale, feedback processes also exist between erosion and sedimentation at the surface and tectonic deformation.
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