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Mantle Strain Localization—How Minerals Deform at Deep Plate Interfaces

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A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Crystallography and Physical Chemistry of Minerals & Nanominerals".

Deadline for manuscript submissions: closed (16 July 2021) | Viewed by 27641

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Dr. Jacques Précigout

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Institut des Sciences de la Terre d'Orléans (ISTO), UMR 7327, CNRS/BRGM, Université d'Orléans, 45071 Orléans, France
Interests: structural geology and tectonics; experimental rock deformation; lithosphere rheology; electron backscatter diffraction

Dr. Cécile Prigent

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Institut de physique du globe de Paris, Université de Paris, CNRS, F-75005 Paris, France
Interests: petrology; microstructures; plate interface rheology; tectonics; seismic cycle; fluid–rock interaction; geochemistry

Dr. Bjarne Almqvist

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Department of Earth Sciences, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden
Interests: dynamics of continental crust and its physical properties; magnetic properties; microstructure; structural geology

Special Issue Information

Dear colleagues,

The Earth-like behavior of lithospheric plates requires strain to be localized at their interfaces, where large parts of the deforming rocks belong to the uppermost mantle. Strain localization into mantle shear zones is a first-order process that governs the displacement of plates from short (seismic) to long (tectonic) timescales. However, the mechanisms that drive mantle strain localization to occur and persist remain poorly understood. Therefore, this Special Issue will address new advances in the deformation of mantle minerals in shear zones dominated by viscous and/or semi-brittle flow. We invite researchers to provide high-quality articles on this topic with a particular emphasis on microstructures, seismic features, and/or rheological properties. Contributions about the role of fluids in mantle strain localization are also strongly encouraged.

Dr. Jacques Précigout
Dr. Cécile Prigent
Dr. Bjarne Almqvist
Guest Editors

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Keywords

mantle minerals
microstructures
mineral fabrics
crystal plasticity
grain boundary sliding
fluid-rock interactions
brittle-ductile transition
seismic wave propagation
seismic anisotropy

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Published Papers (10 papers)

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Editorial

Jump to: Research

2 pages, 194 KiB

Open AccessEditorial

Editorial for Special Issue “Mantle Strain Localization—How Minerals Deform at Deep Plate Interfaces”

by Jacques Précigout, Cécile Prigent and Bjarne Almqvist

Minerals 2022, 12(12), 1625; https://doi.org/10.3390/min12121625 - 16 Dec 2022

Viewed by 1087

Abstract

Understanding Earth’s interior dynamics, the origin and factors of which maintain the present-day plate-like behavior of the lithosphere on our planet, is one of the main goals of geosciences [...] Full article

(This article belongs to the Special Issue Mantle Strain Localization—How Minerals Deform at Deep Plate Interfaces)

Research

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30 pages, 35980 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Ductile vs. Brittle Strain Localization Induced by the Olivine–Ringwoodite Transformation

by Julien Gasc, Blandine Gardonio, Damien Deldicque, Clémence Daigre, Arefeh Moarefvand, Léo Petit, Pamela Burnley and Alexandre Schubnel

Minerals 2022, 12(6), 719; https://doi.org/10.3390/min12060719 - 4 Jun 2022

Cited by 4 | Viewed by 2860

Abstract

As it descends into the Earth’s mantle, the olivine that constitutes the lithosphere of subducting slabs transforms to its high-pressure polymorphs, wadsleyite and ringwoodite, in the so-called transition zone. These transformations have important rheological consequences, since they may induce weakening, strain localization, and, in some cases, earthquakes. In this study, germanium olivine (Ge-olivine) was used as an analogue material to investigate the rheology of samples undergoing the olivine–ringwoodite transformation. Ge-olivine adopts a ringwoodite structure at pressures ~14 GPa lower than its silicate counterpart does, making the transformation accessible with a Griggs rig. Deformation experiments were carried out in a new-generation Griggs apparatus, where micro-seismicity was recorded in the form of acoustic emissions. A careful analysis of the obtained acoustic signal, combined with an extensive microstructure analysis of the recovered samples, provided major insights into the interplay between transformation and deformation mechanisms. The results show that significant reaction rates cause a weakening via the implementation of ductile shear zones that can be preceded by small brittle precursors. When kinetics are more sluggish, mechanical instabilities lead to transformational faulting, which stems from the unstable propagation of shear bands localizing both strain and transformation. The growth of these shear bands is self-sustained thanks to the negative volume change and the exothermic nature of the reaction, and leads to dynamic rupture, as attested by the acoustic emissions recorded. These micro-earthquakes share striking similarities with deep focus earthquakes, which may explain several seismological observations such as magnitude frequency relations and the occurrence of deep repeating earthquakes and foreshocks. Full article

(This article belongs to the Special Issue Mantle Strain Localization—How Minerals Deform at Deep Plate Interfaces)

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25 pages, 9469 KiB

Open AccessArticle

Strain Localization at Constant Strain Rate and Changing Stress Conditions: Implications for Plate Boundary Processes in the Upper Mantle

by Julie Newman, Vasileios Chatzaras, Basil Tikoff, Jan R. Wijbrans, William M. Lamb and Martyn R. Drury

Minerals 2021, 11(12), 1351; https://doi.org/10.3390/min11121351 - 30 Nov 2021

Cited by 5 | Viewed by 2310

Abstract

We present results from a natural deformed shear zone in the Turon de Técouère massif of the French Pyrenees that directly addresses the processes involved in strain localization, a topic that has been investigated for the last 40 years by structural geologists. Paleopiezometry indicates that differential stresses are variable both spatially across the zone, and temporally during exhumation. We have, however, also calculated strain rate, which remains constant despite changes in stress. This result appears to be at odds with recent experimental deformation on monophase (olivine) rocks, which indicate that strain localization occurs dominantly as a result of constant stress. We hypothesize that in the Turon de Técouère massif—and many natural shear zones—strain localization occurs as a result of reactions, which decrease the grain size and promote the activation of grain size sensitive deformation mechanisms. From a tectonics perspective, this study indicates that the deformation rate in a particular plate boundary is relatively uniform. Stress, however, varies to accommodate this deformation. This viewpoint is consistent with deformation at a plate boundary, but it is not the typical way in which we interpret strain localization. Full article

(This article belongs to the Special Issue Mantle Strain Localization—How Minerals Deform at Deep Plate Interfaces)

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22 pages, 9503 KiB

Open AccessArticle

Formation of Ultramylonites in an Upper Mantle Shear Zone, Erro-Tobbio, Italy

by Jolien Linckens and Sören Tholen

Minerals 2021, 11(10), 1036; https://doi.org/10.3390/min11101036 - 24 Sep 2021

Cited by 5 | Viewed by 2254

Abstract

Deformation in the upper mantle is localized in shear zones. In order to localize strain, weakening has to occur, which can be achieved by a reduction in grain size. In order for grains to remain small and preserve shear zones, phases have to mix. Phase mixing leads to dragging or pinning of grain boundaries which slows down or halts grain growth. Multiple phase mixing processes have been suggested to be important during shear zone evolution. The importance of a phase mixing process depends on the geodynamic setting. This study presents detailed microstructural analysis of spinel bearing shear zones from the Erro-Tobbio peridotite (Italy) that formed during pre-alpine rifting. The first stage of deformation occurred under melt-free conditions, during which clinopyroxene and olivine porphyroclasts dynamically recrystallized. With ongoing extension, silica-undersaturated melt percolated through the shear zones and reacted with the clinopyroxene neoblasts, forming olivine–clinopyroxene layers. Furthermore, the melt reacted with orthopyroxene porphyroclasts, forming fine-grained polymineralic layers (ultramylonites) adjacent to the porphyroclasts. Strain rates in these layers are estimated to be about an order of magnitude faster than within the olivine-rich matrix. This study demonstrates the importance of melt-rock reactions for grain size reduction, phase mixing and strain localization in these shear zones. Full article

(This article belongs to the Special Issue Mantle Strain Localization—How Minerals Deform at Deep Plate Interfaces)

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18 pages, 8780 KiB

Open AccessArticle

Dislocation Creep of Olivine and Amphibole in Amphibole Peridotites from Åheim, Norway

by Sejin Jung, Takafumi Yamamoto, Jun-ichi Ando and Haemyeong Jung

Minerals 2021, 11(9), 1018; https://doi.org/10.3390/min11091018 - 18 Sep 2021

Cited by 5 | Viewed by 2921

Abstract

Amphibole peridotite samples from Åheim, Norway, were analyzed to understand the deformation mechanism and microstructural evolution of olivine and amphibole through the Scandian Orogeny and subsequent exhumation process. Three Åheim amphibole peridotite samples were selected for detailed microstructural analysis. The Åheim amphibole peridotites exhibit porphyroclastic texture, abundant subgrain boundaries in olivine, and the evidence of localized shear deformation in the tremolite-rich layer. Two different types of olivine lattice preferred orientations (LPOs) were observed: B- and A-type LPOs. Electron backscatter diffraction (EBSD) mapping and transmission electron microscopy (TEM) observations revealed that most subgrain boundaries in olivine consist of dislocations with a (001)[100] slip system. The subgrain boundaries in olivine may have resulted from the deformation of olivine with moderate water content. In addition, TEM observations using a thickness-fringe method showed that the free dislocations of olivine with the (010)[100] slip system were dominant in the peridotites. Our data suggest that the subgrain boundaries and free dislocations in olivine represent a product of later-stage deformation associated with the exhumation process. EBSD mapping of the tremolite-rich layer revealed intracrystalline plasticity in amphibole, which can be interpreted as the activation of the (100)[001] slip system. Full article

(This article belongs to the Special Issue Mantle Strain Localization—How Minerals Deform at Deep Plate Interfaces)

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18 pages, 18835 KiB

Open AccessArticle

Microstructural Analysis of a Mylonitic Mantle Xenolith Sheared at Laboratory-like Strain Rates from the Edge of the Wyoming Craton

by Yuval Boneh, Emily J. Chin and Greg Hirth

Minerals 2021, 11(9), 995; https://doi.org/10.3390/min11090995 - 10 Sep 2021

Cited by 3 | Viewed by 2513

Abstract

Combined observations from natural and experimental deformation microstructures are often used to constrain the rheological properties of the upper mantle. However, relating natural and experimental deformation processes typically requires orders of magnitude extrapolation in strain rate due to vastly different time scales between nature and the lab. We examined a sheared peridotite xenolith that was deformed under strain rates comparable to laboratory shearing time scales. Microstructure analysis using an optical microscope and electron backscatter diffraction (EBSD) was done to characterize the bulk crystallographic preferred orientation (CPO), intragrain misorientations, subgrain boundaries, and spatial distribution of grains. We found that the microstructure varied between monophase (olivine) and multiphase (i.e., olivine, pyroxene, and garnet) bands. Olivine grains in the monophase bands had stronger CPO, larger grain size, and higher internal misorientations compared with olivine grains in the multiphase bands. The bulk olivine CPO suggests a dominant (010)[100] and secondary activated (001)[100] that are consistent with the experimentally observed transition of the A to E-types. The bulk CPO and intragrain misorientations of olivine and orthopyroxene suggest that a coarser-grained initial fabric was deformed by dislocation creep coeval with the reduction of grain size due to dynamic recrystallization. Comparing the deformation mechanisms inferred from the microstructure with experimental flow laws indicates that the reduction of grain size in orthopyroxene promotes activation of diffusion creep and suggests a high activation volume for wet orthopyroxene dislocation creep. Full article

(This article belongs to the Special Issue Mantle Strain Localization—How Minerals Deform at Deep Plate Interfaces)

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19 pages, 5083 KiB

Open AccessFeature PaperArticle

Rheological Contrast between Quartz and Coesite Generates Strain Localization in Deeply Subducted Continental Crust

by Kouhei Asano, Katsuyoshi Michibayashi and Tomohiro Takebayashi

Minerals 2021, 11(8), 842; https://doi.org/10.3390/min11080842 - 4 Aug 2021

Cited by 3 | Viewed by 2930

Abstract

Deformation microstructures of peak metamorphic conditions in ultrahigh-pressure (UHP) metamorphic rocks constrain the rheological behavior of deeply subducted crustal material within a subduction channel. However, studies of such rocks are limited by the overprinting effects of retrograde metamorphism during exhumation. Here, we present the deformation microstructures and crystallographic-preferred orientation data of minerals in UHP rocks from the Dabie–Shan to study the rheological behavior of deeply subducted continental material under UHP conditions. The studied samples preserve deformation microstructures that formed under UHP conditions and can be distinguished into two types: high-strain mafic–ultramafic samples (eclogite and garnet-clinopyroxenite) and low-strain felsic samples (jadeite quartzite). This distinction suggests that felsic rocks are less strained than mafic–ultramafic rocks under UHP conditions. We argue that the phase transition from quartz to coesite in the felsic rocks may explain the microstructural differences between the studied mafic–ultramafic and felsic rock samples. The presence of coesite, which has a higher strength than quartz, may result in an increase in the bulk strength of felsic rocks, leading to strain localization in nearby mafic–ultramafic rocks. The formation of shear zones associated with strain localization under HP/UHP conditions can induce the detachment of subducted crustal material from subducting lithosphere, which is a prerequisite for the exhumation of UHP rocks. These findings suggest that coesite has an important influence on the rheological behavior of crustal material that is subducted to coesite-stable depths. Full article

(This article belongs to the Special Issue Mantle Strain Localization—How Minerals Deform at Deep Plate Interfaces)

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16 pages, 4414 KiB

Open AccessArticle

Non-Dilatant Brittle Deformation and Strength Reduction of Olivine Gabbro due to Hydration

by Yuya Akamatsu, Kumpei Nagase and Ikuo Katayama

Minerals 2021, 11(7), 694; https://doi.org/10.3390/min11070694 - 28 Jun 2021

Cited by 1 | Viewed by 2364

Abstract

To investigate the influence of hydration on brittle deformation of oceanic crustal rocks, we conducted triaxial deformation experiments on gabbroic rocks with various degrees of hydration at a confining pressure of 20 MPa and room temperature, measuring elastic wave velocity. Hydrated olivine gabbros reached a maximum differential stress of 225–350 MPa, which was considerably less than those recorded for gabbros (~450 MPa), but comparable to those for serpentinized ultramafic rocks (250–300 MPa). Elastic wave velocities of hydrated olivine gabbros did not show a marked decrease even prior to failure. This indicated that the deformation of hydrated olivine gabbro is not associated with the opening of the stress-induced cracks that are responsible for dilatancy. Microstructural observations of the samples recovered after deformation showed crack damage to be highly localized to fault zones with no trace of stress-induced crack opening, consistent with the absence of dilatancy. These data suggest that strain localization of hydrated olivine gabbro can be caused by the development of shear cracks in hydrous minerals such as serpentine and chlorite, even when they are present in only small amounts. Our results suggest that the brittle behavior of the oceanic crust may considerably change due to limited hydration. Full article

(This article belongs to the Special Issue Mantle Strain Localization—How Minerals Deform at Deep Plate Interfaces)

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30 pages, 6651 KiB

Open AccessArticle

Reduced Viscosity of Mg₂GeO₄ with Minor MgGeO₃ between 1000 and 1150 °C Suggests Solid-State Lubrication at the Lithosphere–Asthenosphere Boundary

by Thomas P. Ferrand and Damien Deldicque

Minerals 2021, 11(6), 600; https://doi.org/10.3390/min11060600 - 3 Jun 2021

Cited by 5 | Viewed by 3256

Abstract

Tectonic plates are thought to move above the asthenosphere due to the presence of accumulated melts or volatiles that result in a low-viscosity layer, known as lithosphere–asthenosphere boundary (LAB). Here, we report experiments suggesting that the plates may slide through a solid-state mechanism. Ultrafine-grained aggregates of Mg₂GeO₄ and minor MgGeO₃ were synthetized using spark plasma sintering (SPS) and deformed using a 1-atm deformation rig between 950 °C and 1250 °C. For 1000 < T < 1150 °C, the derivative of the stress–strain relation of the material drops down to zero once a critical stress as low as 30–100 MPa is reached. This viscosity reduction is followed by hardening. The deformation curves are consistent with what is commonly observed in steels during the shear-induced transformation from austenite to martensite, the final material being significantly harder. This is referred to as TRansformation-Induced Plasticity (TRIP), widely observed in metal alloys (TRIP alloys). It should be noted that such enhanced plasticity is not necessarily due to a phase transition, but could consist of any kind of transformation, including structural transformations. We suspect a stress-induced grain-boundary destabilization. This could be associated to the transient existence of a metastable phase forming in the vicinity of grain boundaries between 1000 and 1150 °C. However, no such phase can be observed in the recovered samples. Whatever its nature, the rheological transition seems to occur as a result of a competition between diffusional processes (i.e., thermally activated) and displacive processes (i.e., stress-induced and diffusionless). Consequently, the material would be harder at 1200 °C than at 1100 °C thanks to diffusion that would strengthen thermodynamically stable phases or grain-boundary structures. This alternative scenario for the LAB would not require volatiles. Instead, tectonic plates may slide on a layer in which the peridotite is constantly adjusting via a grain-boundary transformation. Full article

(This article belongs to the Special Issue Mantle Strain Localization—How Minerals Deform at Deep Plate Interfaces)

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27 pages, 4275 KiB

Open AccessArticle

Conductive Channels in the Deep Oceanic Lithosphere Could Consist of Garnet Pyroxenites at the Fossilized Lithosphere–Asthenosphere Boundary

by Thomas P. Ferrand

Minerals 2020, 10(12), 1107; https://doi.org/10.3390/min10121107 - 10 Dec 2020

Cited by 5 | Viewed by 3733

Abstract

Magnetotelluric (MT) surveys have identified anisotropic conductive anomalies in the mantle of the Cocos and Nazca oceanic plates, respectively, offshore Nicaragua and in the eastern neighborhood of the East Pacific Rise (EPR). Both the origin and nature of these anomalies are controversial as well as their role in plate tectonics. The high electrical conductivity has been hypothesized to originate from partial melting and melt pooling at the lithosphere–asthenosphere boundary (LAB). The anisotropic nature of the anomaly likely highlights high-conductivity channels in the spreading direction, which could be further interpreted as the persistence of a stable liquid silicate throughout the whole oceanic cycle, on which the lithospheric plates would slide by shearing. However, considering minor hydration, some mantle minerals can be as conductive as silicate melts. Here I show that the observed electrical anomaly offshore Nicaragua does not correlate with the LAB but instead with the top of the garnet stability field and that garnet networks suffice to explain the reported conductivity values. I further propose that this anomaly actually corresponds to the fossilized trace of the early-stage LAB that formed near the EPR about 23 million years ago. Melt-bearing channels and/or pyroxenite underplating at the bottom of the young Cocos plate would transform into garnet-rich pyroxenites with decreasing temperature, forming solid-state high-conductivity channels between 40 and 65 km depth (1.25–1.9 GPa, 1000–1100 °C), consistently with experimental petrology. Full article

(This article belongs to the Special Issue Mantle Strain Localization—How Minerals Deform at Deep Plate Interfaces)

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