scholarly journals On the possible mechanism of the diamonds formation in Kamchatka mantle wedge.

2017 ◽  
Author(s):  
Alexander Simakin
Keyword(s):  
Thermal Decomposition ◽  
Subduction Zone ◽  
Mantle Wedge ◽  
Rapid Heating ◽  
Stability Field ◽  
Carbonic Fluid ◽  
Mantle Olivine

Various geodynamic mechanisms can lead to the penetration of siliceous carbonates into the mantle wedge. Their thermal decomposition in the “mantle olivine autoclave” can be a mechanism for the formation of diamond erupted in subduction zone of Kamchatka. Using the theory of poro-elasticity, we showed that rapid heating of a mixture of sideritic dolomite and silica at 150-200oC can lead to an increase in pressure by 2-3 GPa. With the initial parameters P = 2 GPa and T = 830oC, the carbonic fluid produced during the reaction would get into the PT stability field of the diamond. The growth of diamond in the PT field of metastable graphite can be enhanced by microparticles of native Ni and Mn formed by the thermal decomposition of gaseous carbonyls. The corresponding abundant micro-inclusions of Ni and Mn are found in Kamchatka diamonds.

scholarly journals Dehydration of chlorite explains anomalously high electrical conductivity in the mantle wedges

2016 ◽  
Vol 2 (5) ◽  
pp. e1501631 ◽  
Author(s):  
Geeth Manthilake ◽  
Nathalie Bolfan-Casanova ◽  
Davide Novella ◽  
Mainak Mookherjee ◽  
Denis Andrault
Keyword(s):  
Electrical Conductivity ◽  
Subduction Zone ◽  
Mantle Wedge ◽  
Aqueous Fluid ◽  
Stability Field ◽  
Initial Increase ◽  
High Electrical Conductivity ◽  
Additional Source ◽  
Slab Dehydration ◽  
Subducting Slab

Mantle wedge regions in subduction zone settings show anomalously high electrical conductivity (~1 S/m) that has often been attributed to the presence of aqueous fluids released by slab dehydration. Laboratory-based measurements of the electrical conductivity of hydrous phases and aqueous fluids are significantly lower and cannot readily explain the geophysically observed anomalously high electrical conductivity. The released aqueous fluid also rehydrates the mantle wedge and stabilizes a suite of hydrous phases, including serpentine and chlorite. In this present study, we have measured the electrical conductivity of a natural chlorite at pressures and temperatures relevant for the subduction zone setting. In our experiment, we observe two distinct conductivity enhancements when chlorite is heated to temperatures beyond its thermodynamic stability field. The initial increase in electrical conductivity to ~3 × 10−3S/m can be attributed to chlorite dehydration and the release of aqueous fluids. This is followed by a unique, subsequent enhancement of electrical conductivity of up to 7 × 10−1S/m. This is related to the growth of an interconnected network of a highly conductive and chemically impure magnetite mineral phase. Thus, the dehydration of chlorite and associated processes are likely to be crucial in explaining the anomalously high electrical conductivity observed in mantle wedges. Chlorite dehydration in the mantle wedge provides an additional source of aqueous fluid above the slab and could also be responsible for the fixed depth (120 ± 40 km) of melting at the top of the subducting slab beneath the subduction-related volcanic arc front.

The rheology of talc at high P-T conditions with implications for subduction-zone dynamics

2020 ◽  
Author(s):  
Yuval Boneh ◽  
Matej Pec ◽  
Greg Hirth
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Mantle Wedge ◽  
Microstructural Analysis ◽  
Stability Field ◽  
Localized Deformation ◽  
Hydrous Minerals ◽  
Regional Seismicity ◽  
Pressure Threshold ◽  
Confining Pressures

<p>Subduction-zone dynamics, kinematics, and seismicity are strongly affected by the rheology of hydrous phyllosilicates. Although there is growing evidence for hydrous minerals in the subducting plate, mantle wedge, and the interface between the plates, we are continuing to learn more about the rheological behavior of phyllosilicates at the relevant pressures. Talc is stable to depths of ≈100 km and has been found in fault rocks and subduction-zones mélanges as the product of metasomatism and/or mineral breakdown (e.g., breakdown of antigorite). The frictional strength of talc under low to intermediate pressures (up to ~400 MPa) was studied and demonstrated some of the mineral’s unique rheology; however, there is a lack of data for pressures of P > 0.5 GPa. Here we present the first rheological and microstructural analysis of experimentally deformed talc under pressure and temperature conditions relevant for the rheology of a subducted slab or mantle wedge.</p><p>We analyzed the mechanical and microstructural evolution of 15 samples of natural talc cylinders deformed using a high P-T deformation ‘Griggs’ type apparatus. We used natural samples comprise of >98 % talc and analyzed the post-mortem microstructure and chemistry of the samples using optical microscopy, scanning electron microscopy, and electron microprobe. The experiments were performed at confining pressures from 0.5 to 2 GPa and temperatures of 25 to 700°C; all within the talc stability field. Results show that the strength of talc at 25°C or 400°C is pressure-dependent up to the highest pressure tested (2 GPa). This behavior is attributed to brittle/semi-brittle mechanisms. At higher temperatures (500-700° C) and above a pressure threshold the strength becomes independent of pressure (e.g., when P > 1 GPa at T = 600 ° C), indicating that dilatant cracking is suppressed at these pressures. However, microstructural analysis indicates that fracturing is evident in all samples at all conditions examined. Interestingly, samples deformed at higher temperatures (>600°C) show more localized deformation. A synthesis of results from this study and previously published studies demonstrate that the strength of talc only becomes temperature-dependent at higher pressures. It is suggested that an increasing P-T geotherm of a subducted slab is likely to induce weakening and localization of talc-rich layers with possible implications for the mechanism to induce/hinder regional seismicity and affect the plate-coupling between the subducted and riding plates.   </p>

Synthesis of Sic Fine Particles by Gas-Phase Reaction Under Short-Time Microgravity

1992 ◽  
Vol 286 ◽  
Author(s):  
Takeshi Okutani ◽  
Yoshinori Nakata ◽  
Masaakt Suzuki ◽  
Yves Maniette ◽  
Nobuyoshi Goto ◽  
...  
Keyword(s):  
Thermal Decomposition ◽  
Heat Source ◽  
Size Distribution ◽  
Gas Phase ◽  
Fine Particles ◽  
Rapid Heating ◽  
Exothermic Reaction ◽  
Phase Reaction ◽  
Gas Phase Reaction ◽  
Short Time

ABSTRACTSiC fine particles were synthesized by the gas-phase thermal decomposition of tetramethylsilane (Si(CH3)4) in hydrogen under microgravity of 10−4G for 10 sec. Rapid heating to the temperature over 800°C which is required for thermal decomposition of Si(CH3)4) under short-time microgravity was attained using a chemical oven where the heat of exothermic reaction of combustion synthesis of Ti-A1-4B composites was used as the heat source. Monodisperse and spherical SiC fine particles were synthesized under microgravity, whereas aggregates of SiC fine particles were synthesized under 1 G gravity. The SiC particles synthesized under microgravity (150-200 nm) were bigger in size and narrower in size distribution than those under 1 G gravity (100-150 nm).

scholarly journals Seismic evidence for flow in the hydrated mantle wedge of the Ryukyu subduction zone

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Takayoshi Nagaya ◽  
Andrew M. Walker ◽  
James Wookey ◽  
Simon R. Wallis ◽  
Kazuhiko Ishii ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Mantle Wedge

Explosive Thermal Decomposition Mechanism of NTO

1995 ◽  
Vol 418 ◽  
Author(s):  
David J. Beardall ◽  
Tod R. Botcher ◽  
Charles A. Wight
Keyword(s):  
Thin Films ◽  
Thermal Decomposition ◽  
Fourier Transform ◽  
Infrared Spectroscopy ◽  
Condensed Phase ◽  
Decomposition Product ◽  
Rapid Heating ◽  
Initial Step ◽  
Thermal Decomposition Mechanism ◽  
Decomposition Products

AbstractThe initial step of the thermal decomposition of NTO (5-nitro-2,4-dihydro-3H-1,2,4- triazol-3-one) is determined by pulsed infrared laser pyrolysis of thin films. Rapid heating of the film and quenching to 77 K allows one to trap the initial decomposition products in the condensed phase and analyze them using transmission Fourier-transform infrared spectroscopy. The initial decomposition product is CO2; NO2 and HONO are not observed. We propose a new mechanism for NTO decomposition in which CO2 is formed.

scholarly journals Ophiolitic Pyroxenites Record Boninite Percolation in Subduction Zone Mantle

Minerals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 565 ◽  
Author(s):  
Véronique Le Roux ◽  
Yan Liang
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Mantle Wedge ◽  
Major Element ◽  
Early Stage ◽  
Diffusion Modeling ◽  
Melt Infiltration ◽  
Melt Percolation ◽  
Back Arc ◽  
Parental Melts

The peridotite section of supra-subduction zone ophiolites is often crosscut by pyroxenite veins, reflecting the variety of melts that percolate through the mantle wedge, react, and eventually crystallize in the shallow lithospheric mantle. Understanding the nature of parental melts and the timing of formation of these pyroxenites provides unique constraints on melt infiltration processes that may occur in active subduction zones. This study deciphers the processes of orthopyroxenite and clinopyroxenite formation in the Josephine ophiolite (USA), using new trace and major element analyses of pyroxenite minerals, closure temperatures, elemental profiles, diffusion modeling, and equilibrium melt calculations. We show that multiple melt percolation events are required to explain the variable chemistry of peridotite-hosted pyroxenite veins, consistent with previous observations in the xenolith record. We argue that the Josephine ophiolite evolved in conditions intermediate between back-arc and sub-arc. Clinopyroxenites formed at an early stage of ophiolite formation from percolation of high-Ca boninites. Several million years later, and shortly before exhumation, orthopyroxenites formed through remelting of the Josephine harzburgites through percolation of ultra-depleted low-Ca boninites. Thus, we support the hypothesis that multiple types of boninites can be created at different stages of arc formation and that ophiolitic pyroxenites uniquely record the timing of boninite percolation in subduction zone mantle.

The southwestern edge of the Ryukyu subduction zone: A high Q mantle wedge

2012 ◽  
Vol 335-336 ◽  
pp. 145-153 ◽  
Author(s):  
Yen-Ting Ko ◽  
Ban-Yuan Kuo ◽  
Kuo-Lung Wang ◽  
Shu-Chuan Lin ◽  
Shu-Huei Hung
Keyword(s):  
Subduction Zone ◽  
Mantle Wedge ◽  
High Q

Thermal state of the upper mantle and the origin of the Cambrian-Ordovician ophiolite pulse: Constraints from ultramafic dikes of the Hayachine-Miyamori ophiolite

2020 ◽  
Vol 105 (12) ◽  
pp. 1778-1801
Author(s):  
Takafumi Kimura ◽  
Kazuhito Ozawa ◽  
Takeshi Kuritani ◽  
Tsuyoshi Iizuka ◽  
Mitsuhiro Nakagawa
Keyword(s):  
Mantle Source ◽  
Upper Mantle ◽  
Mantle Wedge ◽  
Thermal State ◽  
Potential Temperature ◽  
Geochemical Data ◽  
Small Scale ◽  
Stability Field ◽  
Depleted Mantle ◽  
Slab Breakoff

Abstract Ophiolite pulses, which are periods of enhanced ophiolite generation and emplacement, are thought to have a relevance to highly active superplumes (superplume model). However, the Cambrian-Ordovician pulse has two critical geological features that cannot be explained by such a superplume model: predominance of subduction-related ophiolites and scarcity of plume-related magma activities. We addressed this issue by estimating the mechanism and condition of magma generation, including mantle potential temperature (MPT), from a ~500 Ma subduction-related ophiolite, the Hayachine-Miyamori ophiolite. We developed a novel method to overcome difficulties in global MPT estimation from an arc environment by using porphyritic ultramafic dikes showing flow differentiation, which have records of the chemical composition of the primitive magma, including its water content, because of their high pressure (~0.6 GPa) intrusion and rapid solidification. The solidus conditions for the primary magmas are estimated to be ~1450 °C, ~5.3 GPa. Geochemical data of the dikes show passive upwelling of a depleted mantle source in the garnet stability field without a strong influence of slab-derived fluids. These results, combined with the extensive fluxed melting of the mantle wedge prior to the dike formation, indicate sudden changes of the melting environment, its mechanism, and the mantle source from extensive fluxed melting of the mantle wedge to decompressional melting of the sub-slab mantle, which has been most plausibly triggered by a slab breakoff. The estimated MPT of the sub-slab mantle is ~1350 °C, which is very close to that of the current upper mantle and may reflect the global value of the upper mantle at ~500 Ma if small-scale convection maintained the shallow sub-slab mantle at a steady thermal state. We, therefore, conclude that the Cambrian-Ordovician ophiolite pulse is not attributable to the high temperature of the upper mantle. Frequent occurrence of slab breakoff, which is suggested by our geochemical compilation of Cambrian-Ordovician ophiolites, and subduction termination, which is probably related to the assembly of the Gondwana supercontinent, may be responsible for the ophiolite pulse.

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