3. Minerals and the interior of the Earth

2014 ◽  
Author(s):  
David Vaughan
Keyword(s):  
Upper Mantle ◽  
Lower Mantle ◽  
Plate Tectonics ◽  
Inner Core ◽  
Indirect Evidence ◽  
Outer Core ◽  
The Earth ◽  
Granite Formation ◽  
Temperature And Pressure

‘Minerals and the interior of the Earth’ looks at the role of minerals in plate tectonics during the processes of crystallization and melting. The size and range of minerals formed are dependent on the temperature and pressure of the magma during its movement through the crust. The evolution of the continental crust also involves granite formation and processes of metamorphism. Our understanding of the interior of the Earth is based on indirect evidence, mainly the study of earthquake waves. The Earth consists of concentric shells: a solid inner core; liquid outer core; a solid mantle divided into a lower mantle, a transition zone, and an upper mantle; and then the outer rigid lithosphere.

scholarly journals The fate of water within Earth and super-Earths and implications for plate tectonics

2017 ◽  
Vol 375 (2094) ◽  
pp. 20150394 ◽  
Author(s):  
Sonia M. Tikoo ◽  
Linda T. Elkins-Tanton
Keyword(s):  
Upper Mantle ◽  
Plate Tectonics ◽  
Extrasolar Planets ◽  
Internal Heat ◽  
Magma Ocean ◽  
Nominally Anhydrous Minerals ◽  
The Earth ◽  
Giant Impacts ◽  
Crystallographic Defects

The Earth is likely to have acquired most of its water during accretion. Internal heat of planetesimals by short-lived radioisotopes would have caused some water loss, but impacts into planetesimals were insufficiently energetic to produce further drying. Water is thought to be critical for the development of plate tectonics, because it lowers viscosities in the asthenosphere, enabling subduction. The following issue persists: if water is necessary for plate tectonics, but subduction itself hydrates the upper mantle, how is the upper mantle initially hydrated? The giant impacts of late accretion created magma lakes and oceans, which degassed during solidification to produce a heavy atmosphere. However, some water would have remained in the mantle, trapped within crystallographic defects in nominally anhydrous minerals. In this paper, we present models demonstrating that processes associated with magma ocean solidification and overturn may segregate sufficient quantities of water within the upper mantle to induce partial melting and produce a damp asthenosphere, thereby facilitating plate tectonics and, in turn, the habitability of Earth-like extrasolar planets. This article is part of the themed issue ‘The origin, history and role of water in the evolution of the inner Solar System’.

HIGHER ORDER THERMOELASTIC PROPERTIES OF THE EARTH LOWER MANTLE AND CORE

2010 ◽  
Vol 24 (09) ◽  
pp. 1187-1200 ◽  
Author(s):  
S. S. KUSHWAH ◽  
N. K. BHARDWAJ
Keyword(s):  
Bulk Modulus ◽  
Lower Mantle ◽  
Inner Core ◽  
Outer Core ◽  
Higher Order ◽  
Grüneisen Parameter ◽  
Free Volume Theory ◽  
Gruneisen Parameter ◽  
The Earth ◽  
Derivatives Of

We have used some of the most reliable high pressure equations of state (EOS) to determine the thermoelastic Grüneisen parameter and its higher order volume derivatives for the lower mantle, outer core and inner core of the Earth. The cross derivatives of bulk modulus with respect to pressure and temperature have also been obtained for the deep interior of the Earth using the results based on the modified free volume theory for the Grüneisen parameter. We have used five EOS viz. (a) modified Rydberg EOS, (b) modified Poirier–Tarantola EOS, (c) Hama–Suito EOS, (d) Stacey EOS, and (e) Kushwah EOS to determine pressure derivatives of bulk modulus. The results for thermoelastic parameters obtained in the present study show systematic variations with the increase in pressure.

On the fate of water in the formation of rocky planets

2021 ◽  
Author(s):  
Lindy Elkins-Tanton ◽  
Jenny Suckale ◽  
Sonia Tikoo
Keyword(s):  
Water Content ◽  
Upper Mantle ◽  
Lower Mantle ◽  
Plate Tectonics ◽  
Solidus Temperature ◽  
Magma Ocean ◽  
Excess Water ◽  
Low Degree ◽  
Giant Impacts ◽  
Rocky Planets

<p>Rocky planets go through at least one and likely multiple magma ocean stages, produced by the giant impacts of accretion. Planetary data and models show that giant impacts do not dehydrate either the mantle or the atmosphere of their target planets. The magma ocean liquid consists of melted target material and melted impactor, and so will be dominated by silicate melt, and also contain dissolved volatiles including water, carbon, and sulfur compounds.</p><p>As the magma ocean cools and solidifies, water and other volatiles will be incorporated into the nominally anhydrous mantle phases up to their saturation limits, and will otherwise be enriched in the remaining, evolving magma ocean liquids. The water content of the resulting cumulate mantle is therefore the sum of the traces in the mineral grains, and any water in trapped interstitial liquids. That trapped liquid fraction may in fact be by far the largest contributor to the cumulate water budget.</p><p>The water and other dissolved volatiles in the evolving liquids may quickly reach the saturation limit of magmas near the surface, where pressure is low, but degassing the magma ocean is likely more difficult than has been assumed in some of our models. To degas into the atmosphere, the gases must exsolve from the liquid and form bubbles, and those bubbles must be able to rise quickly enough to avoid being dragged down by convection and re-dissolved at higher pressures. If bubbles are buoyant enough (that is, large enough) to decouple from flow and rise, then they are also dynamically unstable and liable to be torn into smaller bubbles and re-entrained. This conundrum led to the hypothesis that volatiles do not significantly degas until a high level of supersaturation is reached, and the bubbles form a buoyant layer and rise in diapirs in a continuum dynamics sense. This late degassing would have the twin effects of increasing the water content of the cumulates, and of speeding up cooling and solidification of the planet.</p><p>Once the mantle is solidified, the timeclock until the start of plate tectonics begins. Modern plate tectonics is thought to rely on water to lower the viscosity of the asthenosphere, but plate tectonics is also thought to be the process by which water is brought into the mantle. Magma ocean solidification, however, offers two relevant processes. First, following solidification the cumulate mantle is gravitationally unstable and overturns to stability, carrying water-bearing minerals from the upper mantle through the transition zone and into the lower mantle. Upon converting to lower-mantle phases, these minerals will release their excess water, since lower mantle phases have lower saturation limits, thus fluxing the upper mantle with water. Second, the mantle will be near its solidus temperature still, and thus its viscosity will be naturally low. When fluxed with excess water, the upper mantle would be expected to form a low degree melt, which if voluminous enough with rise to help form the earliest crust, and if of very low degree, will further reduce the viscosity of the asthenosphere.</p>

scholarly journals Impact of inner core rotation on outer core flow: the role of outer core viscosity

2004 ◽  
Vol 159 (1) ◽  
pp. 372-389 ◽  
Author(s):  
J. Y. Guo ◽  
P. M. Mathews ◽  
Z. X. Zhang ◽  
J. S. Ning
Keyword(s):  
Inner Core ◽  
Outer Core ◽  
Core Flow ◽  
Core Rotation ◽  
Inner Core Rotation

scholarly journals The Subduction Dichotomy of Strong Plates and Weak Slabs

2016 ◽  
Author(s):  
Robert I. Petersen ◽  
Dave R. Stegman ◽  
Paul J. Tackley
Keyword(s):  
Lower Mantle ◽  
Plate Tectonics ◽  
Material Strength ◽  
Control Material ◽  
The Earth ◽  
Dynamic Forces ◽  
Lithospheric Plates ◽  
Geodynamic Models

Abstract. A key element of plate tectonics on Earth is that the lithosphere is subducting into the mantle. Subduction results from forces that bend and pull the lithosphere into the interior of the Earth. Once subducted, lithospheric slabs are further modified by dynamic forces in the mantle and their sinking is inhibited by the increase in viscosity of the lower mantle. These forces are resisted by the material strength of the lithosphere. Using geodynamic models we investigate several subduction models wherein we control material strength by setting a maximum viscosity for the surface plates and the subducted slabs independently. We find that the models which produce results most analogous to observations of subduction on Earth are characterized by a dichotomy of lithosphere strengths. These models have strong lithospheric plates at the surface which promotes Earth-like single-sided subduction. At the same time these models have weakened lithospheric subducted slabs which pile, bend or lie flat at the top of the lower mantle reproducing the spectrum of slab morphologies observed on Earth.

The Tectonic Plates are Moving!

2018 ◽  
Author(s):  
Roy Livermore
Keyword(s):  
Plate Tectonics ◽  
First Generation ◽  
Volcanic Eruptions ◽  
Short Article ◽  
Tectonic Plates ◽  
The Earth ◽  
Deep Interior ◽  
Two Generations ◽  
The 1960S

Written in a witty and informal style, this book explains modern plate tectonics in a non-technical manner, showing not only how it accounts for phenomena such as great earthquakes, tsunamis, and volcanic eruptions, but also how it controls conditions at the Earth’s surface, including global geography and climate, making it suitable for life. The book presents the advances that have been made since the establishment of plate tectonics in the 1960s, highlighting, on the fiftieth anniversary of the theory, the contributions of a small number of scientists who have never been widely recognized for their discoveries. Beginning with the publication of a short article in Nature by Vine and Matthews, the book traces the development of plate tectonics through two generations of the theory. First-generation plate tectonics covers the exciting scientific revolution of the 1960s, its heroes, and its villains. The second generation includes the rapid expansions in sonar, satellite, and seismic technologies during the 1980s and 1990s that provided a truly global view of the plates and their motions, and an appreciation of the role of their within the Earth system. Arriving at the cutting edge of the science, the latest results from studies using techniques such as seismic tomography and mineral physics to probe the deep interior are discussed and the prospects for finding plate tectonics on other planets assessed. Ultimately, the book leads to the startling conclusion that, without plate tectonics, the Earth would be as lifeless as Venus.

Unraveling the upper mantle heterogeneity from integrated multi-observable inversions

2020 ◽  
Author(s):  
Javier Fullea ◽  
Sergei Lebedev ◽  
Zdenek Martinec ◽  
Nicolas Celli
Keyword(s):  
Seismic Tomography ◽  
Upper Mantle ◽  
Plate Tectonics ◽  
Seismic Velocity ◽  
Gravity Data ◽  
Density Field ◽  
Seismic Velocities ◽  
Satellite Gravity ◽  
The Earth ◽  
Multiple Data Sets

<p>The lateral and vertical thermochemical heterogeneity in the mantle is a long standing question in geodynamics. The forces that control mantle flow and therefore Plate Tectonics arise from the density and viscosity lateral and vertical variations. A common approach to estimate the density field for geodynamical purposes is to simply convert seismic tomography anomalies sometimes assuming constraints from mineral physics. Such converted density field does not match in general with the observed gravity field, typically predicting anomalies the amplitudes of which are too large. Knowledge on the lateral variations in lithospheric density is essential to understand the dynamic/residual isostatic components of the Earth’s topography linking deep and surface processes. The cooling of oceanic lithosphere, the bathymetry of mid oceanic ridges, the buoyancy and stability of continental cratons or the thermochemical structure of mantle plumes are all features central to Plate Tectonics that are dramatically related to mantle temperature and composition.</p><p><br>Conventional methods of seismic tomography, topography and gravity data analysis constrain distributions of seismic velocity and density at depth, all depending on temperature and composition of the rocks within the Earth. However, modelling and interpretation of multiple data sets provide a multifaceted image of the true thermochemical structure of the Earth that needs to be appropriately and consistently integrated. A simple combination of gravity, petrological and seismic models alone is insufficient due to the non-uniqueness and different sensitivities of these models, and the internal consistency relationships that must connect all the intermediate parameters describing the Earth involved. In fact, global Earth models based on different observables often lead to rather different, even contradictory images of the Earth.</p><p><br> Here we present a new global thermochemical model of the lithosphere-upper mantle (WINTERC-grav) constrained by state-of-the-art global waveform tomography, satellite gravity (geoid and gravity anomalies and gradiometric measurements from ESA's GOCE mission), surface elevation and heat flow data. WINTERC-grav is based upon an integrated geophysical-petrological approach where all relevant rock physical properties modelled (seismic velocities and density) are computed within a thermodynamically self-consistent framework allowing for a direct parameterization of the temperature and composition variables.</p>

Viscous drag and the differential rotation of the Earth's core

1997 ◽  
Vol 57 (1) ◽  
pp. 231-233
Author(s):  
DAVID L. BOOK ◽  
J. A. VALDIVIA
Keyword(s):  
Simple Model ◽  
Differential Rotation ◽  
Dynamic Viscosity ◽  
Inner Core ◽  
Outer Core ◽  
Viscous Drag ◽  
Earth’S Rotation ◽  
The Core ◽  
The Earth ◽  
Earth’S Inner Core

It is proposed that the differential rotation of the Earth's inner core deduced by Song and Richards is due to a combination of the deceleration of the Earth's rotation and the viscous drag between the Earth's inner and outer cores. If this model is correct then the dynamic viscosity in the outer core of the Earth can be estimated to be μ≈104 poise. Besides providing a novel way of determining the viscosity of the core, this simple model suggests some new tests and shows how astronomical effects can influence geological phenomena.

Attenuation in the earth at low frequencies

1983 ◽  
Vol 308 (1504) ◽  
pp. 479-522 ◽  
Keyword(s):  
Large Scale ◽  
Inner Core ◽  
Outer Core ◽  
Quality Data ◽  
Low Frequencies ◽  
The Earth ◽  
Relative Standard ◽  
Average Shear ◽  
Standard Deviations ◽  
Apparent Attenuation

The introduction of global, digitally recording, seismic networks has provided the seismological community with a large quantity of high quality data. At low frequencies the IDA (International Deployment of Accelerometers) network provides the best available data and, in this report, over 500 IDA records have been carefully analysed giving nearly 4000 reliable measurements of centre frequency and apparent attenuation of fundamental spheroidal modes. The attenuation rate of a normal mode of free oscillation of the Earth is measured in terms of its or quality factor and mean Q values for the modes 0 S 8 - 0 S 46 are presented with standard deviations of 2-9% . Mean centre frequencies have relative standard deviation of 5 x 10- 5 to 5 x 10- 4 . The distribution of the centre frequencies reveals a large-scale aspherical structure in velocity and density but the distribution of the apparent attenuation measurements does not reveal a corresponding structure. A total of 26 new measurements of the mean Q of overtone modes with standard deviations of 5-30 % have also been obtained by using single-record and multiple-record techniques. Combining the new data with reliable Q measurements from the literature gives a total of 71 data with which we can infer the radial structure of attenuation inside the Earth. This structure is not well constrained in detail and very simple models are capable of fitting the data. Experiments with synthetic data show that an improvement of an order of magnitude in both the number and quality of the measurements is required to make detailed inferences about the structure of attenuation. The data do constrain the average shear Q- 1 in the inner core to be 1/3500 ( ± 60 %) and the average shear Q- 1 the mantle to be 1/250 ( ± 4 %). These values are appropriate for frequencies less than 5 mHz. Comparison with published values at higher frequencies indicates there is a measurable frequency dependence of attenuation between 3 and 30 mHz. Very little can be inferred about bulk dissipation in the Earth beyond that it must exist to satisfy the attenuation of the radial modes. Experiments show that the data can be satisfied if bulk attenuation is an average 1.3%, or more, of the shear attenuation. Constraining bulk attenuation to be no greater than 2 % of the shear attenuation, and constraining the outer core to have no attenuation, forces bulk attenuation to be concentrated in the upper mantle.

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