scholarly journals Microstructural Evolution of Amphibole Peridotites in Åheim, Norway, and the Implications for Seismic Anisotropy in the Mantle Wedge

Minerals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 345 ◽  
Author(s):  
Sejin Jung ◽  
Haemyeong Jung ◽  
Håkon Austrheim
Keyword(s):  
Mantle Wedge ◽  
Seismic Anisotropy ◽  
Microstructural Analysis ◽  
Dislocation Creep ◽  
Hydrous Minerals ◽  
Fine Grained ◽  
Lattice Preferred Orientation ◽  
Initial Stage ◽  
Dominant Deformation Mechanism ◽  
Rich Condition

The microstructure of amphibole peridotites from Åheim, Norway were analyzed to understand the evolution of the lattice-preferred orientation (LPO) of olivine throughout the Scandian Orogeny and its implication for the seismic anisotropy of the subduction zone. The Åheim peridotites had a porphyroclastic texture and some samples contained an abundant amount of hydrous minerals such as tremolite. Detailed microstructural analysis on the Åheim peridotites revealed multiple stages of deformation. The coarse grains showed an A-type LPO of olivine, which can be interpreted as the initial stage of deformation. The spinel-bearing samples showed a mixture of B-type and C-type LPOs of olivine, which is considered to represent the deformation under water-rich conditions. The recrystallized fine-grained olivine displays a B-type LPO, which can be interpreted as the final stage of deformation. Microstructures and water content of olivine indicate that the dominant deformation mechanism of olivine showing a B-type LPO is a dislocation creep under water-rich condition. The observation of the B-type LPO of olivine is important for an interpretation of trench-parallel seismic anisotropy in the mantle wedge. The calculated seismic anisotropy of the tremolite showed that tremolite can contribute to the trench-parallel seismic anisotropy in the mantle wedge.

Deformation microstructure of amphibole peridotite from Aheim, Norway and its implication for the seismic anisotropy of the mantle wedge

2020 ◽  
Author(s):  
Sejin Jung ◽  
Haemyeong Jung ◽  
Håkon Austrheim
Keyword(s):  
Mantle Wedge ◽  
Seismic Anisotropy ◽  
Microstructural Analysis ◽  
Localized Deformation ◽  
Western Gneiss Region ◽  
Hydrous Minerals ◽  
Fine Grained ◽  
Rich Condition ◽  
Fabric Strength ◽  
The One

<p>The microstructures of amphibole peridotites from the Åheim, Norway were studied to understand the evolution of microstructures of olivine through the Scandian Orogeny and the subsequent exhumation process. The Western Gneiss Region, Norway had undergone UHP metamorphism and subsequent retrogression associated with the Scandian Orogeny. The Åheim amphibole peridotite shows clear porphyroclastic texture, abundant hydrous minerals such as tremolite or chlorite, and much evidence of localized deformation. LPOs of olivine and amphibole were determined by using electron back-scattered diffraction (EBSD) system attached to the scanning electron microscope (SEM).</p><p>Detailed microstructural analysis on the Åheim amphibole peridotites revealed the evidence of the multiple stages of deformation during the Scandian Orogeny. The coarse grains of olivine including porphyroclasts showed the A-type LPO of olivine (Jung & Karato, 2001), which is interpreted as an initial stage of deformation. The recrystallized-fine grains of olivine showed the B-type LPO of olivine (Jung & Karato, 2001), which is interpreted as a late-stage deformation in amphibolite facies condition. Observation of abundant hydrous minerals, hydrous inclusions in olivine, as well as high dislocation density of olivine in the fine-grained olivines suggest that fabric transition of olivine from the A-type to B-type LPO was resulted from the deformation in a water-rich condition during the exhumation process. The B-type LPO of olivine is important because it is the one of the possible mechanisms for causing the trench-parallel seismic anisotropy in the mantle wedge. A partial fabric transition from the A-type to the B-type LPO of olivine associated with the localized deformation in a water-rich condition might explain a weak seismic anisotropy observed in NE Japan or Mexico. Amphiboles in the amphibole-rich layer showed the Type-III LPO of amphibole (Ko & Jung, 2015). It is found that strong fabric strength and the resultant seismic anisotropy of amphibole can perform a similar role as other hydrous minerals such as serpentine or chlorite on the trench-parallel seismic anisotropy with the flow dipping along the subducting slab in the mantle wedge.</p><p> </p><p>Jung, H., Karato, S., 2001, Science, 293, 1460-1463.</p><p>Ko, B., Jung, H., 2015, Nature Communications, 6: 6586.</p>

Experimental investigation of antigorite dehydration fabrics at high pressure and high temperature

2020 ◽  
Author(s):  
Junfeng Zhang ◽  
Wenlong Liu ◽  
Yongfeng Wang
Keyword(s):  
Mantle Wedge ◽  
Seismic Anisotropy ◽  
Coarse Grained ◽  
Anisotropic Fluid ◽  
Plate Boundaries ◽  
Intermediate Depth ◽  
Fine Grained ◽  
Serpentinized Peridotite ◽  
Type C ◽  
Convergent Plate Boundaries

<p>Antigorite dehydration is well known as a key process in convergent boundaries for the genesis of mantle wedge partial melting and intermediate-depth earthquakes. However, the crystallographic preferred orientations (CPOs) of prograde minerals from antigorite dehydration and its effects on seismic anisotropy of subducting slabs remain ambiguous and controversial. Here we report hydrostatic dehydration experiments on foliated serpentinized peridotite at pressures of 0.3-6 GPa and temperatures of 700-900 °C. Our results show that the orientations of prograde olivine inherit orientations from adjacent olivine grains in the olivine-rich layer by epitaxial growth. In contrast, olivine CPOs evolved with the grain size from fiber-[001] featuring clear [100] point maxima and [001] girdles for fine-grained olivine to orthorhombic patterns characterized by clear [100] and [001] point maxima for coarse-grained olivine, i.e., type-C CPO. We propose that the fine-grained fiber-[001] CPO is developed by topotactic growth at the onset of dehydration, while the orthorhombic type-C CPO for the coarse-grained olivine, especially the [001] point maximum along the lineation, is mainly developed by anisotropic growth resulting from anisotropic fluid flow during the dehydration. The developed olivine type-C CPO in the antigorite-rich layer after antigorite dehydration could explain the trench or strike parallel seismic anisotropy observed at convergent plate boundaries.</p>

Lattice preferred orientation of talc and implications for seismic anisotropy

2020 ◽  
Author(s):  
Jungjin Lee ◽  
Haemyeong Jung ◽  
Reiner Klemd ◽  
Matthew Tarling ◽  
Dmitry Konopelko
Keyword(s):  
High Pressure ◽  
Subduction Zones ◽  
Seismic Anisotropy ◽  
Preferred Orientation ◽  
Azimuthal Anisotropy ◽  
Hydrous Minerals ◽  
Ultra High Pressure ◽  
Lattice Preferred Orientation ◽  
Radial Anisotropy ◽  
First Time

<p>Strong seismic anisotropy is generally observed in subduction zones. Lattice preferred orientation (LPO) of olivine and elastically anisotropic hydrous minerals has been considered to be an important factor causing anomalous seismic anisotropy. For the first time, we report on measured LPOs of polycrystalline talc. The study comprises subduction-related ultra-high-pressure metamorphic schists from the Makbal Complex in Kyrgyzstan-Kazakhstan and amphibolite-facies metasomatic schists from the Valla Field Block in Unst, Scotland. The here studied talc revealed a strong alignment of [001] axes (sub)normal to the foliation and a girdle distribution of [100] axes and (010) poles (sub)parallel to the foliation. The LPOs of polycrystalline talc produced a significant P–wave anisotropy (AVp = 72%) and a high S–wave anisotropy (AVs = 24%). The results imply that the LPO of talc influence both the strong trench-parallel azimuthal anisotropy and positive/negative radial anisotropy of P–waves, and the trench-parallel seismic anisotropy of S–waves in subduction zones.</p>

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>

The effect of composite rheology on mantle convection models with plate-like behavior

2020 ◽  
Author(s):  
Maelis Arnould ◽  
Tobias Rolf
Keyword(s):  
Deformation Mechanism ◽  
Mantle Convection ◽  
Plate Tectonics ◽  
Large Scale ◽  
Seismic Anisotropy ◽  
Dislocation Creep ◽  
Diffusion Creep ◽  
Mantle Flow ◽  
Dynamic Topography ◽  
Lattice Preferred Orientation

<p>The coupling between mantle convection and plate tectonics results in mantle flow patterns and properties which can be characterized with different seismic methods. In particular, the presence of mantle seismic anisotropy in the uppermost mantle suggests the existence of mineral Lattice-Preferred Orientation (LPO) caused by asthenospheric flow. Dislocation creep, which implies non-Newtonian mantle rheology, has been identified as a deformation mechanism responsible for such LPO leading to seismic anisotropy. While it has been proposed that the use of a composite rheology (with both diffusion and dislocation creep) significantly impacts the planform of convection and thus the resulting tectonic behavior at the surface, large-scale mantle convection studies have typically assumed diffusion creep (Newtonian rheology) as the only deformation mechanism, due to computational limitations.</p><p>Here, we investigate the role of composite rheology on mantle convection with self-consistent plate-like behavior using the code StagYY in 2D annulus (Hernlund and Tackley, 2008). We quantify the spatial distribution of dislocation creep in the mantle in models characterized by different transitional stresses between Newtonian and non-Newtonian rheology. Such models are built on previous viscoplastic cases featuring Earth-like plate velocities, surface heat flow and topography with Newtonian rheology (Arnould et al., 2018). We then investigate how composite rheology impacts the planform of convection and the style of plate-like behavior.</p><p> </p><p><strong>References:</strong></p><p>Hernlund, J. W., & Tackley, P. J. (2008). Modeling mantle convection in the spherical annulus. Physics of the Earth and Planetary Interiors, 171(1-4), 48-54.</p><p>Arnould, M., Coltice, N., Flament, N., Seigneur, V., & Müller, R. D. (2018). On the scales of dynamic topography in whole‐mantle convection models. Geochemistry, Geophysics, Geosystems, 19(9), 3140-3163.</p>

scholarly journals Application of the Composite Hardness Models in the Analysis of Mechanical Characteristics of Electrolytically Deposited Copper Coatings: The Effect of the Type of Substrate

Metals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 111
Author(s):  
Ivana O. Mladenović ◽  
Nebojša D. Nikolić ◽  
Jelena S. Lamovec ◽  
Dana Vasiljević-Radović ◽  
Vesna Radojević
Keyword(s):  
Mechanical Characteristics ◽  
Dislocation Creep ◽  
Average Current Density ◽  
Fine Grained ◽  
Copper Coatings ◽  
Electrochemically Deposited ◽  
Composite Models ◽  
Average Current ◽  
Composite Hardness ◽  
Coating Hardness

The mechanical characteristics of electrochemically deposited copper coatings have been examined by application of two hardness composite models: the Chicot-Lesage (C-L) and the Cheng-Gao (C-G) models. The 10, 20, 40 and 60 µm thick fine-grained Cu coatings were electrodeposited on the brass by the regime of pulsating current (PC) at an average current density of 50 mA cm−2, and were characterized by scanning electron (SEM), atomic force (AFM) and optical (OM) microscopes. By application of the C-L model we determined a limiting relative indentation depth (RID) value that separates the area of the coating hardness from that with a strong effect of the substrate on the measured composite hardness. The coating hardness values in the 0.9418–1.1399 GPa range, obtained by the C-G model, confirmed the assumption that the Cu coatings on the brass belongs to the “soft film on hard substrate” composite hardness system. The obtained stress exponents in the 4.35–7.69 range at an applied load of 0.49 N indicated that the dominant creep mechanism is the dislocation creep and the dislocation climb. The obtained mechanical characteristics were compared with those recently obtained on the Si(111) substrate, and the effects of substrate characteristics such as hardness and roughness on the mechanical characteristics of the electrodeposited Cu coatings were discussed and explained.

A Comparative Study on Superplasticity of Mg-Zn-Y-Zr Processed by ECAE and Hot Rolling

2007 ◽  
Vol 551-552 ◽  
pp. 203-208 ◽  
Author(s):  
Wei Neng Tang ◽  
Hong Yan ◽  
Rong Shi Chen ◽  
En Hou Han
Keyword(s):  
Hot Rolling ◽  
Superplastic Deformation ◽  
Rate Sensitivity ◽  
Sensitivity Coefficient ◽  
Grain Boundary Sliding ◽  
Diffusional Creep ◽  
Dislocation Creep ◽  
Fine Grained ◽  
Microstructure Observation ◽  
Elongation To Failure

Superplastic deformation (SPD) behaviors of two fine-grained materials produced by ECAE and hot rolling methods have been contrastively studied in this paper. It is found that the optimum superplastic condition in as-ECAEed material was at 350°C and 1.7×10-3s-1 with elongation to failure about 800%; while in as-rolled material, the largest elongation to failure about 1000% was obtained at 480°C and 5.02×10-4s-1. Microstructure observation showed that grain evolution and cavitation behavior were different in these two materials during superplastic deformation. The controlled mechanisms for superplasticity, i.e. grain boundary sliding (GBS), dislocation creep and diffusional creep, at different deformation conditions were discussed in terms of strain rate sensitivity coefficient, stress exponent and activity energy.

scholarly journals Overriding plate, mantle wedge, slab, and subslab contributions to seismic anisotropy beneath the northern Central Andean Plateau

2016 ◽  
Vol 17 (7) ◽  
pp. 2556-2575 ◽  
Author(s):  
Maureen D. Long ◽  
C. Berk Biryol ◽  
Caroline M. Eakin ◽  
Susan L. Beck ◽  
Lara S. Wagner ◽  
...  
Keyword(s):  
Mantle Wedge ◽  
Seismic Anisotropy
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