scholarly journals Tracking slab surface temperatures with electrical conductivity of glaucophane

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Geeth Manthilake ◽  
Ye Peng ◽  
Kenneth T. Koga ◽  
Mainak Mookherjee
Keyword(s):  
Electrical Conductivity ◽  
Low Temperatures ◽  
Silicate Melts ◽  
Slab Surface ◽  
Dehydration Melting ◽  
Hydrous Minerals ◽  
First Order ◽  
Slab Temperature ◽  
Thermodynamic Instability ◽  
Subducting Slab

AbstractSlab surface temperature is one of the key parameters that incur first-order changes in subduction dynamics. However, the current thermal models are based on empirical thermal parameters and do not accurately capture the complex pressure–temperature paths of the subducting slab, prompting significant uncertainties on slab temperature estimations. In this study, we investigate whether the dehydration-melting of glaucophane can be used to benchmark the temperature in the slab. We observe that dehydration and melting of glaucophane occur at relatively low temperatures compared to the principal hydrous phases in the slab and produce highly conductive Na-rich melt. The electrical properties of glaucophane and its dehydration products are notably different from the hydrous minerals and silicate melts. Hence, we conclude that the thermodynamic instability of glaucophane in the slab provides a unique petrological criterion for tracking temperature in the present-day subduction systems through magnetotelluric profiles.

scholarly journals Sediment-Peridotite Reaction Controls Fore-Arc Metasomatism and Arc Magma Geochemical Signatures

Geosciences ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 372
Author(s):  
Michael W. Förster ◽  
Yannick Bussweiler ◽  
Dejan Prelević ◽  
Nathan R. Daczko ◽  
Stephan Buhre ◽  
...  
Keyword(s):  
Trace Elements ◽  
Low Temperatures ◽  
Slab Surface ◽  
High Field Strength ◽  
Arc Magmas ◽  
Selective Incorporation ◽  
Partial Melts ◽  
Subducting Slab ◽  
Arc Magma ◽  
Distribution Of Trace Elements

Subduction of oceanic crust buries an average thickness of 300–500 m of sediment that eventually dehydrates or partially melts. Progressive release of fluid/melt metasomatizes the fore-arc mantle, forming serpentinite at low temperatures and phlogopite-bearing pyroxenite where slab surface reaches 700–900 °C. This is sufficiently high to partially melt subducted sediments before they approach the depths where arc magmas are formed. Here, we present experiments on reactions between melts of subducted sediments and peridotite at 2–6 GPa/750–1100 °C, which correspond to the surface of a subducting slab. The reaction of volatile-bearing partial melts derived from sediments with depleted peridotite leads to separation of elements and a layered arrangement of metasomatic phases, with layers consisting of orthopyroxene, mica-pyroxenite, and clinopyroxenite. The selective incorporation of elements in these metasomatic layers closely resembles chemical patterns found in K-rich magmas. Trace elements were imaged using LA-ICP-TOFMS, which is applied here to investigate the distribution of trace elements within the metasomatic layers. Experiments of different duration enabled estimates of the growth of the metasomatic front, which ranges from 1–5 m/ky. These experiments explain the low contents of high-field strength elements in arc magmas as being due to their loss during melting of sedimentary materials in the fore-arc.

scholarly journals Behavior and properties of water in silicate melts under deep mantle conditions

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Bijaya B. Karki ◽  
Dipta B. Ghosh ◽  
Shun-ichiro Karato
Keyword(s):  
Electrical Conductivity ◽  
Molar Volume ◽  
Water Solution ◽  
Pure Water ◽  
Electrical Conductance ◽  
Water Structure ◽  
Bulk Water ◽  
Silicate Melts ◽  
Pressure Regime ◽  
Low Pressures

AbstractWater (H2O) as one of the most abundant fluids present in Earth plays crucial role in the generation and transport of magmas in the interior. Though hydrous silicate melts have been studied extensively, the experimental data are confined to relatively low pressures and the computational results are still rare. Moreover, these studies imply large differences in the way water influences the physical properties of silicate magmas, such as density and electrical conductivity. Here, we investigate the equation of state, speciation, and transport properties of water dissolved in Mg1−xFexSiO3 and Mg2(1−x)Fe2xSiO4 melts (for x = 0 and 0.25) as well as in its bulk (pure) fluid state over the entire mantle pressure regime at 2000–4000 K using first-principles molecular dynamics. The simulation results allow us to constrain the partial molar volume of the water component in melts along with the molar volume of pure water. The predicted volume of silicate melt + water solution is negative at low pressures and becomes almost zero above 15 GPa. Consequently, the hydrous component tends to lower the melt density to similar extent over much of the mantle pressure regime irrespective of composition. Our results also show that hydrogen diffuses fast in silicate melts and enhances the melt electrical conductivity in a way that differs from electrical conduction in the bulk water. The speciation of the water component varies considerably from the bulk water structure as well. Water is dissolved in melts mostly as hydroxyls at low pressure and as –O–H–O–, –O–H–O–H– and other extended species with increasing pressure. On the other hand, the pure water behaves as a molecular fluid below 15 GPa, gradually becoming a dissociated fluid with further compression. On the basis of modeled density and conductivity results, we suggest that partial melts containing a few percent of water may be gravitationally trapped both above and below the upper mantle-transition region. Moreover, such hydrous melts can give rise to detectable electrical conductance by means of electromagnetic sounding observations.

Solid to superionic transition in iron oxide-hydroxide

2021 ◽  
Author(s):  
Qingyang Hu ◽  
Mingqiang Hou ◽  
Yu He
Keyword(s):  
Electrical Conductivity ◽  
Extreme Pressure ◽  
Hydrous Minerals ◽  
Water Ice ◽  
Individual Unit ◽  
Freely Moving ◽  
Superionic Transition ◽  
Increasing Temperature ◽  
Isotopic Mixing ◽  
Redox Equilibria

<p>At planetary interior conditions, water ice has been proved to enter a superionic phase recently since it was predicted about 30-year ago. Hydrogen in superionic water become liquid-like, and move freely within solid oxygen lattice. Under extreme pressure and temperature conditions of Earth’s deep mantle, the solid-superionic transition can also occur readily in the pyrite-type FeO<sub>2</sub>Hx, a candidate mineral in the lower mantle and probably also in other hydrous minerals. We find that when the pressure increases beyond 73 GPa at room temperature, symmetric hydroxyl bonds are softened and the H<sup>+</sup> (or proton) become diffusive within the vicinity of its crystallographic site. Increasing temperature under pressure, the diffusivity of hydrogen is extended beyond individual unit cell to cover the entire solid, and the electrical conductivity soars, indicating a transition to the superionic state which is characterized by freely-moving proton and solid FeO<sub>2</sub> lattice. The superionic hydrogen will dramatically change the geophysical picture of electrical conductivity and magnetism, as well as geochemical processes of hydrogen isotopic mixing and redox equilibria at local regions of Earth’s deep interiors.</p>

THE THERMAL DECOMPOSITION OF HYDROGEN PEROXIDE VAPOUR. II.

1947 ◽  
Vol 25b (2) ◽  
pp. 135-150 ◽  
Author(s):  
Paul A. Giguère
Keyword(s):  
Activation Energy ◽  
Hydrogen Peroxide ◽  
Thermal Decomposition ◽  
Low Temperatures ◽  
Hydrocyanic Acid ◽  
Quartz Surface ◽  
First Order ◽  
Acid Washing ◽  
Reaction Vessels ◽  
Low Pressures

The decomposition of hydrogen peroxide vapour has been investigated at low pressures (5 to 6 mm.) in the temperature range 50° to 420 °C., for the purpose of determining the effect of the nature and treatment of the active surfaces. The reaction was followed in an all-glass apparatus and, except in one case, with one-litre round flasks as reaction vessels. Soft glass, Pyrex, quartz, and metallized surfaces variously treated were used. In most cases the decomposition was found to be mainly of the first order but the rates varied markedly from one vessel to another, even with vessels made of the same type of glass. On a quartz surface the decomposition was preceded by an induction period at low temperatures. Fusing the glass vessels slowed the reaction considerably and increased its apparent activation energy; this effect was destroyed by acid washing. Attempts to poison the surface with hydrocyanic acid gave no noticeable result. The marked importance of surface effects at all temperatures is considered as an indication that the reaction was predominantly heterogeneous under the prevailing conditions. Values ranging from 8 to 20 kcal. were found for the apparent energy of activation. It is concluded that the decomposition of hydrogen peroxide vapour is not very specific as far as the nature of the catalyst is concerned.

scholarly journals A theoretical study of a possible model of paramagnetic alums at low temperatures

1940 ◽  
Vol 176 (965) ◽  
pp. 203-213 ◽  
Keyword(s):  
Magnetic Field ◽  
Low Temperatures ◽  
Theoretical Study ◽  
Spontaneous Magnetization ◽  
Critical Value ◽  
Transition Curve ◽  
Thin Specimen ◽  
First Order ◽  
Freely Suspended ◽  
Line Of Critical Points

An attempt is made to examine theoretically the properties of paramagnetic alums at low temperatures. The model taken is a lattice of freely suspended magnets, all interactions except purely magnetic being neglected. Even with this simplification it is impossible at present to make rigorous calculations of the partition function, either on classical or quantum lines. A simple model is proposed, which is really a generalization of the Bragg - Williams theory enabling one to take account of the effect of a magnetic field. The few configurations whose energies are known are used to fix arbitrary constants in the expression assumed for the energy. The theory predicts that the state of lowest energy is either a spontaneously magnetized, state for a long thin specimen, or a state in which alternate rows of magnets point in opposite directions for a sphere, spontaneous magnetization appearing in an ellipsoid with an eccentricity greater than a certain critical value. The transition curve bounding the region in which the antiparallel state is stable consists partly of a line of Curie points corresponding to transitions of the second, order, passing smoothly into a line of critical points corresponding to a transition of the first order. The effect of shape on the magnetic properties of the specimen seems to be experimentally verified, but the rough nature of the theory prevents it being more than qualitative.

scholarly journals TEMPERATURE CHARACTERISTICS FOR THE METABOLISM OF CHLORELLA

1934 ◽  
Vol 18 (2) ◽  
pp. 209-213 ◽  
Author(s):  
C. S. French
Keyword(s):  
Hydrogen Peroxide ◽  
Low Temperatures ◽  
Temperature Characteristics ◽  
First Order

The decomposition of hydrogen peroxide by intact Chlorella cells follows a first order course at very low temperatures, but at higher temperatures gives falling first order constants. Between 0.6° and 20°C. the value of µ is 10,500 calories.

On the Green-function theory of the spin- Heisenberg ferromagnet

1968 ◽  
Vol 46 (9) ◽  
pp. 1021-1028 ◽  
Author(s):  
S. T. Dembinski
Keyword(s):  
Green Function ◽  
Curie Temperature ◽  
Low Temperatures ◽  
Random Phase Approximation ◽  
Function Theory ◽  
Random Phase ◽  
Exact Result ◽  
Heisenberg Ferromagnet ◽  
First Order ◽  
The Green Function

A new first-order decoupling scheme for the Green function appearing in the theory of the spin-[Formula: see text] Heisenberg ferromagnet is introduced. At low temperatures the magnetization has no spurious term in T3 and the coefficient of the term in T4 is within a few percent of the Dyson exact result. The Curie temperature is equal to the random phase approximation Curie temperature.

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