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| Volume expansion of super-hydrated kaolinite. a,b, Pressure-and temperature-induced changes in the lattice parameters (a) and unit cell volume and calculated density (b) of kaolinite.
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Water is the most abundant volatile component in the Earth. It continuously enters the mantle through subduction zones, where it reduces the melting temperature of rocks to generate magmas. The dehydration process in subduction zones, which determines whether water is released from the slab or transported into the deeper mantle, is an essential com...
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... range between around 200 °C and 500 °C at pressures between 2.5(1) GPa and 5.0(1) GPa (Fig. 1b and Supplementary Fig. 4). After pressure release, the (001) reflection with a d spacing of ~10 Å disappears, indicating revers- ible water intercalation. Changes in the lattice parameters and unit cell volumes throughout this transition are depicted in Fig. 2 (see also Supplementary Table 3). The length of the c axis contracts gradually by 0.12(1) Å while the a and b axes contract by 0.05(2) Å up to pressures near 2.5(1) GPa (Fig. 2a). Such an anisotropic con- traction is also found in smectite 26 . Above 2.7(1) GPa and heating at 200 °C for 1 hour, the c axis length increases by about 32% ...
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... spacing of ~10 Å disappears, indicating revers- ible water intercalation. Changes in the lattice parameters and unit cell volumes throughout this transition are depicted in Fig. 2 (see also Supplementary Table 3). The length of the c axis contracts gradually by 0.12(1) Å while the a and b axes contract by 0.05(2) Å up to pressures near 2.5(1) GPa (Fig. 2a). Such an anisotropic con- traction is also found in smectite 26 . Above 2.7(1) GPa and heating at 200 °C for 1 hour, the c axis length increases by about 32% while the a and b axis lengths decrease by 1.96% and 0.52%, respectively (Fig. 2a). This results in the expansion of the unit cell volume by approximately 31 % (Fig. 2b). This now ...
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... gradually by 0.12(1) Å while the a and b axes contract by 0.05(2) Å up to pressures near 2.5(1) GPa (Fig. 2a). Such an anisotropic con- traction is also found in smectite 26 . Above 2.7(1) GPa and heating at 200 °C for 1 hour, the c axis length increases by about 32% while the a and b axis lengths decrease by 1.96% and 0.52%, respectively (Fig. 2a). This results in the expansion of the unit cell volume by approximately 31 % (Fig. 2b). This now super-hydrated kaolinite seems to be less stable under pressure, showing a smaller bulk modulus of K 0 = 49.80(1) GPa compared with K 0 = 57.38(1) GPa for kaolinite before super-hydration. The calculated density of the super-hydrated ...
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... near 2.5(1) GPa (Fig. 2a). Such an anisotropic con- traction is also found in smectite 26 . Above 2.7(1) GPa and heating at 200 °C for 1 hour, the c axis length increases by about 32% while the a and b axis lengths decrease by 1.96% and 0.52%, respectively (Fig. 2a). This results in the expansion of the unit cell volume by approximately 31 % (Fig. 2b). This now super-hydrated kaolinite seems to be less stable under pressure, showing a smaller bulk modulus of K 0 = 49.80(1) GPa compared with K 0 = 57.38(1) GPa for kaolinite before super-hydration. The calculated density of the super-hydrated kaolinite is also found to be lower than the original phase at ambient conditions, that is, ...
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... seems to be less stable under pressure, showing a smaller bulk modulus of K 0 = 49.80(1) GPa compared with K 0 = 57.38(1) GPa for kaolinite before super-hydration. The calculated density of the super-hydrated kaolinite is also found to be lower than the original phase at ambient conditions, that is, 2.48(6) g cm −3 versus 2.61(1) g cm −3 (Fig. 2b). The lower density and K 0 of super- hydrated kaolinite compared with the original phase at ambient conditions indicates that it might transform or break down into dense phases at higher pressures and temperatures along the subduction ...
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... structural model of the super- hydrated kaolinite sheds new light on the origin of the hydrated analogue of kaolinite, halloysite (Al 2 Si 2 O 5 (OH) 4 ·2H 2 O). Our experimental data show that when halloysite is compressed in the presence of water, the intensity of its basal reflection at d ≈ 10 Å increases, indicating that additional water insertion forms a phase similar to the super-hydrated kaolinite with three H 2 O molecule per unit cell ( Supplementary Fig. 2b). It is also interesting to note the contrasting morphologies of kaolinite and halloysite at ambient conditions. ...
Citations
... However, it is surprising that high-pressure and hightemperature (HP-HT) studies of clay minerals are scarce, compared to those of crustal minerals and serpentines, although understanding the stabilities of clay minerals, especially along the water-rich subduction interface, would provide new insights into the origins of the ASH system and related deep H 2 O transport into the Earth 24,25 . In our previous work, we have demonstrated that subducting kaolinite (Al 2 Si 2 O 5 (OH) 4 ), one of the representative oceanic clay sediments in the ASH system, increases its H 2 O transport capacity via superhydration, i.e., a counter-intuitive mineral transformation in which a hydrated mineral uptakes more water to form a further hydrated mineral; kaolinite becomes super-hydrated (Al 2 Si 2 O 5 (OH) 4 ·3H 2 O) at a depth of about 75 km along a water-rich cold subduction interface, which subsequently breaks down near 200 km depth to form other minerals in the ASH system 26 . This work called for the need for reevaluating the overall impacts of subducting clays for the origins of the ASH minerals and water transportation into the deep Earth. ...
... Pyrophyllite (Al 2 Si 4 O 10 (OH) 2 ) is a hydrous clay mineral consisting of a sheet of aluminum dioctahedra sandwiched between two layers of silicon tetrahedra, representing the so-called 2:1 clay mineral group in the ASH system. Similar to kaolinite, a representative clay for the 1:1 group 26 , pyrophyllite does not possess interlayer cations nor water molecules at ambient conditions and hence is nominally 'nonexpandable', making it an ideal candidate to examine the possible intercalations of water, i.e., super-hydration, under the subduction interface environment. Pyrophyllite usually occurs in low-grade metamorphosed Al-rich sediments and also in high-pressure/lowtemperature metamorphic rocks 27 . ...
... As a high-pressure vessel, a symmetric-type diamond-anvil cell (DAC) equipped with a pair of type-I anvils of culet diameter of 300 µm or 500 µm was used in combination with a membrane device for online pressure control. A rhenium gasket Pyrophyllite and water reacts to form the gibbsite + diaspore + coesite assemblage (this study), while kaolinite and water reacts to form super-hydrated kaolinite 26 . c topaz + diaspore + coesite assemblage is formed in the upper mantle region along the breakdown sequence from pyrophyllite (this study), while phase-pi + diaspore + coesite is formed along that of super-hydrated kaolinite 26 . ...
Subducting sedimentary layer typically contains water and hydrated clay minerals. The stability of clay minerals under such hydrous subduction environment would therefore constraint the lithology and physical properties of the subducting slab interface. Here we show that pyrophyllite (Al2Si4O10(OH)2), one of the representative clay minerals in the alumina-silica-water (Al2O3-SiO2-H2O, ASH) system, breakdowns to contain further hydrated minerals, gibbsite (Al(OH)3) and diaspore (AlO(OH)), when subducts along a water-saturated cold subduction geotherm. Such a hydration breakdown occurs at a depth of ~135 km to uptake water by ~1.8 wt%. Subsequently, dehydration breakdown occurs at ~185 km depth to release back the same amount of water, after which the net crystalline water content is preserved down to ~660 km depth, delivering a net amount of ~5.0 wt% H2O in a phase assemblage containing δ-AlOOH and phase Egg (AlSiO3(OH)). Our results thus demonstrate the importance of subducting clays to account the delivery of ~22% of water down to the lower mantle.
... The interlayer gaps in the structure of apophyllite-type compounds are densely packed, with no vacancies in them. Recent studies of the behavior of layered silicates compressed in a water-containing fluid (Hwang et al. 2017(Hwang et al. , 2020Basu and Mookherjee 2021) have shown that the penetration of the H 2 O molecules into the structure of kaolin group minerals requires not only high pressure, but also a temperature of about 200 °C. However, the study of fluorapophyllite-(K) at simultaneously high pressure (HP) and high temperature (HT) up to 9 GPa and 225 °C shows the absence of the PIH effect (Likhacheva et al. 2023). ...
The high-pressure structural evolution of a natural hydroxyapophyllite-(K) K0.96 Ca4.01[Al0.01Si7.99O20]((OH)0.95F0.05)·(H2O)8.14, Z = 2, a = 8.9699(1), c = 15.8934(3) Å, space group P4/mnc, from the Hatrurim Basin, Negev Desert, compressed in penetrating (ethanol:water 8:1 mixture) medium up to 5 GPa, was studied by single-crystal X-ray diffraction with a diamond anvil cell. The results clearly demonstrate the absence of pressure-induced hydration in the structure. Within 3 GPa, the compression mechanism is similar to that known in fluorapophyllite-(K). The compression in the plane of silicate layer proceeds via the relative rotation of the four-membered rings. The compression along the c-axis proceeds through the shortening of the inter-layer distance, whereas the thickness of silicate layer remains almost unchanged. As a result, the pressure-induced changes in the unit-cell metrics are similar to those for fluorapophyllite-(K). At about 3 GPa, hydroxyapophyllite-(K) undergoes a phase transition with the symmetry lowering to orthorhombic (space group Pnnm). The symmetry of the high-pressure phase allows deformation of the four-membered rings of the silicate layer, which is impossible within tetragonal symmetry. In this case, the structure is compressed much more along the a-axis than along the b-axis. As a result, the orthorhombic phase of hydroxyapophyllite-(K) is more compressible compared to fluorapophyllite-(K).
... [14] Reversible pressure-induced swelling transitions were found later for GO in several polar solvents, [11,15] synthetic [16] and natural clays. [17] This effect is observed when hydrophilic 2D material is compressed in liquid solvent and undergoes swelling transition due to expansion of inter-layer lattice caused by insertion of additional solvent, either as well defined layers or in "liquid-like" state. Reversible swelling transitions between, for example, oneand two-layered solvate phases were found in high-pressure experiments with GO in alcohols [15c,18] and synthetic hectorite in water. ...
Pressure‐induced swelling has been reported earlier for several hydrophilic layered materials. MXene Ti3C2Tx is also a hydrophilic layered material composed by 2D sheets but so far pressure‐induced swelling is reported for this material only under conditions of shear stress at MPa pressures. Here, high‐pressure experiments are performed with MXenes prepared by two methods known to provide “clay‐like” materials. MXene synthesized by etching MAX phase with HCl+LiF demonstrates the effect of pressure‐induced swelling at 0.2 GPa with the insertion of additional water layer. The transition is incomplete with two swollen phases (ambient with d(001) = 16.7Å and pressure‐induced with d(001) = 19.2Å at 0.2 GPa) co‐existing up to the pressure point of water solidification. Therefore, the swelling transition corresponds to change from two‐layer water intercalation (2L‐phase) to a never previously observed three‐layer water intercalation (3L‐phase) of MXene. Experiments with MXene prepared by LiCl+HF etching have not revealed pressure‐induced swelling in liquid water. Both MXenes also show no anomalous compressibility in liquid methanol. The presence of pressure‐induced swelling only in one of the MXenes indicates that the HCl+LiF synthesis method is likely to result in higher abundance of hydrophilic functional groups terminating 2D titanium carbide.
... Although the cation exchange capacity of kaolinite is extremely low owing to the hydrogen-bonded interlayer region, it is now known that if the hydrogen bonding is weakened, kaolinite does participate in cation exchange reactions with several organic molecules including acetamide, dimethyl sulphoxide (DMSO), dimethyl acetamide, dimethyl formamide, formamide, hydrazine, N methyl acetamide, N methyl formamide, pyridine N oxide, and urea (Johnston, 2010). In a recent study, intercalation of water has been reported in kaolinite at high pressures and temperatures, a phenomenon referred to as pressure-induced hydration (PIH) (Hwang et al., 2017(Hwang et al., , 2019Basu and Mookherjee, 2021). It is speculated that such pressure-induced hydration is likely to transport significantly more water into the Earth's interior. ...
... A key question is what structural changes does kaolinite undergo to facilitate such intercalation at high pressures? So far only a few studies examined the structural changes of kaolinite and its structural polytypes at high pressures (Johnston et al., 2002;Dera et al., 2003;Welch and Crichton, 2010;Welch et al., 2012;Hwang et al., 2017;Michalski et al., 2017;Basu and Mookherjee, 2021;Hong et al., 2022). The high-pressure studies based on X-ray diffraction have proposed polytypic transformations (Dera et al., 2003;Welch and Crichton, 2010). ...
Kaolinite is formed by weathering of continental crustal rocks and is also found in marine sediments in the tropical region. Kaolinite and other layered hydrous silicate minerals are likely to play a vital role in transporting water into the Earth's interior via subducting slabs. Recent studies have experimentally documented the expansion of the interlayer region by intercalation of water molecules at high pressures i.e., pressure-induced hydration. This is counter-intuitive since the interlayer region in the layered silicates is quite compressible, so it is important to understand the underlying mechanism that causes intercalation and expansion of the interlayer region.
To address this, we explore the high-pressure behavior of natural kaolinite from Keokuk, Iowa. This sample is free of anatase impurities and thus helps to examine both low-energy (0–1200 cm−1) and high-energy hydroxyl (3000–4000 cm−1) regions using Raman spectroscopy and synchrotron-based powder X-ray diffraction.
Our results show that the pressure dependence of the hydroxyl modes exhibits discontinuities at ∼3 GPa and ∼ 6.5 GPa. This is related to the polytypic transformation of Kaolinite from K-1 to K-II and K-II to K-III phase. Several low-energy Raman modes' pressure dependence also exhibits similar discontinuous behavior. The synchrotron-based powder X-ray diffraction results also indicate discontinuous behavior in the pressure dependence of the unit-cell volume and lattice parameters. The analysis of the bulk and the linear compressibility reveals that kaolinite is extremely anisotropic and is likely to aid its geophysical detectability in subduction zone settings. The K-I to K-II polytypic transition is marked by the snapping of hydrogen bonds, thus at conditions relevant to the Earth's interior, water molecules intercalate in the interlayer region and stabilize the crystal structure and help form the super-hydrated kaolinite which can transport significantly more water into the Earth's interior.
... However, the ultimate origin of this magmatic water remains ambiguous. It is controversial whether water originates from metasomatized subcontinental lithospheric mantle through interaction with dry mantle plumes, or mantle plumes are "wet" due to the presence of recycled crustal material in the plume source (Dixon et al., 2002;Tappe et al., 2006;Hwang et al., 2017;Kuritani et al., 2019;Wang et al., 2022a). ...
... Based on the measurement of hydrogen concentrations in olivine phenocrysts, our previous studies reveal high water contents of the primitive aillikite melts and their upper mantle source (∼300-400 ppm; Wang et al., 2022a). Water in these magmas may originate from (1) metasomatized subcontinental lithospheric mantle through interaction with melts derived from a relatively "dry" plume source, or mantle plumes that are "wet" because of (2) recycling of subducted crustal material (Dixon et al., 2002;Tappe et al., 2006;Hu et al., 2017;Hwang et al., 2017). The subcontinental lithospheric mantle is highly heterogeneous regarding its age and geochemical composition due to multiple events of partial melting and metasomatism (e.g., Carlson and Irving, 1994). ...
Water is known to play a crucial role in the generation of many large igneous provinces (LIP) worldwide, but the amount and origin of the water in their sources is still under debate. To address this question, this paper presents in situ major-, trace-element, and Sr isotope data coupled with bulk-mineral O-H-He isotope analyses of amphibole in a suite of aillikites from the Tarim LIP (NW China). The cores of zoned macrocrysts and microcrysts display partially overlapping compositions ranging between edenite and pargasite (75−83 versus 75−80 Mg#), which suggest a common origin from an evolving magma. The rims (Mg# = 75−80) of both macrocrysts and microcrysts are very similar to their cores for many elements, except for higher Sr and Ba contents. All the amphibole zones show similar primitive mantle−normalized trace element patterns, suggesting that they crystallized at different stages during magmatic evolution. This interpretation is confirmed by the homogenous Sr isotope compositions (87Sr/86Sr(i) = 0.70298−0.70394) of these amphiboles, which overlap with those of magmatic apatites and perovskites in these aillikites. The hydrogen isotope compositions (δD = −120‰ to −140‰) of the amphiboles are significantly lower than average mantle values. Given the low water contents (<0.66 wt%) of these minerals, the low H isotope signatures of the amphiboles might be caused by variable H2O loss during magma ascent. However, open-system Rayleigh fractionation modeling suggests that the hydrogen isotope compositions of these amphibole phenocrysts cannot be fully reproduced by crystallization following magmatic degassing. These low δD values require incorporation of recycled altered oceanic crust containing hydrous components in the plume source of these aillikites, which is consistent with the previously published moderately radiogenic He isotope ratios of olivine separates and bulk-rock Os and Pb isotope data for these same samples. We conclude that water in these magmas was derived from a plume source containing recycled water-bearing oceanic crust.
... When an aqueous fluid coexists with talc or kaolinite (two kinds of phyllosilicate minerals) under high p-T conditions, experiments have shown that water can be adsorbed into the interlayer, forming a subnanometer quasi-two-dimensional water layer (Chinnery et al., 1999;Fumagalli et al., 2001;Hwang et al., 2017). Researchers have considered phyllosilicates with intercalated water to be hydrous mineral phases, which serve as water carriers in the descending slab (Chinnery et al., 1999;Fumagalli et al., 2001;Hwang et al., 2017;Ohtani, 2005Ohtani, , 2015. ...
... When an aqueous fluid coexists with talc or kaolinite (two kinds of phyllosilicate minerals) under high p-T conditions, experiments have shown that water can be adsorbed into the interlayer, forming a subnanometer quasi-two-dimensional water layer (Chinnery et al., 1999;Fumagalli et al., 2001;Hwang et al., 2017). Researchers have considered phyllosilicates with intercalated water to be hydrous mineral phases, which serve as water carriers in the descending slab (Chinnery et al., 1999;Fumagalli et al., 2001;Hwang et al., 2017;Ohtani, 2005Ohtani, , 2015. However, as shown by our thermodynamic study based on atomic simulations, the intercalated water layer is stable only when the water activity of the coexisting fluid is sufficiently high . ...
... Nevertheless, they reveal that for a crystalline interface that does not form hydrogen bonds well, pressure-induced water intercalation is anticipated. Pressure-induced water intercalation has also been observed in talc and kaolinite interlayers Chinnery et al., 1999;Fumagalli et al., 2001;Hwang et al., 2017). Our previous simulation study of talc and kaolinite with multiple crystalline layers stacking under a periodic boundary condition showed that water can be intercalated when pressure is high . ...
During subduction, metamorphic dehydration reactions in the downgoing slab release fluids, generating fluid overpressure. It has been suggested that fluid is driven to flow upward by buoyancy, but a sufficiently high permeability allowing formation of a fluid percolation network is required. Traditionally, fluid percolation has been identified based on the textural equilibrium assumption by measuring the dihedral angle at the triple junction of grains. According to this theory, grain boundaries generally cannot be infiltrated by fluid, and only the grain edge can form a fluid flow channel. We argue that this theory is insufficient because we have found that water from fluid can be adsorbed into the crystalline interface, that is, a layered mineral interlayer, a crack, or a grain boundary. The high pressure in a subducting slab drives water adsorption into the crystalline interface, forming a low‐dimensional fluidic phase, and thus fluid percolation is achieved. Because water adsorbed in the interface is fluidic, water diffusion drives fluid transport in the subducting slab. Due to water adsorption, fluid overpressure at the dehydration front may release, so that dehydration embrittlement may be excluded. Stable water adsorption in the subduction‐slab conditions is determined here by combining molecular dynamics simulations and thermodynamic calculations. Analysis based on simulations shows that water adsorption requires crystalline surfaces which do not form hydrogen bonds well.
... Micas incorporate atomic groups (OH) that can be transformed to water at special thermodynamics conditions: at 100 km Earth's depth, these minerals can be dehydrated and water can be freed in subduction slabs which triggered off important melting processes in Earth crust (Huang and Wyllie 1973;Hwang et al. 2017). Micas along with serpentines can bring water even beyond the arc front depths (Schmidt and Poli 1998;Schmidt et al. 2004). ...
... From stability critical P-T curve, Phl is considered stable at room pressure at critical temperature of 1370 ℃, increasing 118 ℃ its critical temperature each 1 GPa of increasing pressure (Hazen 1977). Phl can undergo dehydroxylation reaction at approximately 200 km depths, but its stability is affected with Ms substitution (Hwang et al. 2017). In general, the thermodynamics stability of these trioctahedral compounds can be affected by the dioctahedral substitutions. ...
Muscovite (Ms) and phlogopite (Phl) series mineral is studied in the 2 M 1 polytype and modeled by the substitution of three Mg ²⁺ cations in the three octahedral sites of Phl [KMg 3 (Si 3 Al)O 10 (OH) 2 ] by two Al ³⁺ and one vacancy, increasing the substitution up to reach the Ms [KAl 2 □(Si 3 Al)O 10 (OH) 2 ]. The series was computationally examined at DFT using Quantum ESPRESSO, as a function of pressure from − 3 to 9 GPa. Crystal structure is calculated, and cell parameters, and geometry of atomic groups agree with experimental values. OH in the Mg ²⁺ octahedrons are approximately perpendicular to the (001) plane, meanwhile when they are in Al ³⁺ , octahedral groups are approximately parallel to this plane. From Quantum Theory of Atoms in Molecules, the atomic basins are calculated as a function of the pressure, K ⁺ and basal O show the largest volumes. The bulk excess volume (Vxs) and the excess atomic volumes are analyzed as a function of the composition and the pressure. K ⁺ , basal and apical O Vxs show a behavior similar to the bulk Vxs as a function of the composition, keeping qualitatively this behavior as a function of pressure; substituent atoms do not show a Vxs behavior similar to the bulk and their effect consequently is mostly translated to atoms in the interlayer space. Atomic compressibilities are also calculated. Atomic compressibilities are separated in the different sheets of the crystal cell. Atomic moduli of K and basal O are the lowest and the ones behaving as the bulk modulus of the series. The atomic bulk modulus of the H’s is different depending of their position with respect to the (001) plane.
... In this case, however, the wick structure was not very strong. Although kaolinite loses the hydroxyl group at a temperature of ~550°C, the super-hydrated phase of kaolinite broke down as pressure and temperature approached ~19 GPa and 800°C (Hwang et al., 2017). The porosity of four sintered samples (100% zeolite, 90/10 zeolite-kaolin, 80/20 zeolite-kaolin, and 70/30 zeolite-kaolin) was measured after preparation using the pressurized sintering method at various temperatures and pressures (Fig. 7). ...
A wick structure is the core part of a heat pipe that produces capillaries to move liquid from a condenser to an evaporator. The purpose of the current study was to develop a wick structure from zeolite and kaolin using various sintering methods. Due to significant porosity and water-adsorption properties, zeolite and kaolin can produce a large capillary force inside the heat pipe. A porous wick specimen is developed from pure zeolite together with a mixture of zeolite and kaolin by using pressureless (loosely packed) and conventional pressurized sintering for thermosiphon heat-pipe applications. Major properties such as porosity, water adsorption, and permeability were noted to be better under pressureless sintering compared to pressurized sintering. Significant and uneven shrinkage in both radial and linear directions is a major problem in loosely packed sintering of pure zeolite. However, the addition of kaolin helps to overcome the problem of shrinkage in pure zeolite; but the permeability and strength of the wick structure are reduced with the addition of kaolin. A general trend is that increasing porosity causes increasing permeability. Due to grain size and compaction, however, permeability is reduced with the addition of kaolin. Based on the experimental results for porosity and permeability, the wick structure formed from zeolite with 5–10% of kaolin has better thermal properties for heat-pipe applications.
... The dehydration of subducted rocks causes melting of the mantle, which results in volcanic and tectonic activity and ensures stable supplies of fluids and melts (Graham et al., 2008). These fluids not only change the thermal structure of the subducted plate but also influence the structure and construction of the overlying mantle transition zone (Hwang et al., 2017;Okazaki and Hirth, 2016). Slab dehydration plays an important role in megathrust seismicity (Miller et al., 2003). ...
The calamitous phreatomagmatic eruption of the Hunga Tonga–Hunga Ha'apai (HTHH) volcano in January 2022 has been reported to have had a volcanic explosivity index (VEI) of 5-6 and a column height of 20 km and to have caused powerful tsunamis across the Pacific. Along the subvolcanic heterogeneous and tightly coupled megathrusts, the hydrothermal structure is considered essential to the deep arc volcanism and catalysis of focused interplate earthquakes. However, at present, such heterogeneity in slab hydrothermal regimes and the linkage of slab metamorphism to seismotectonics and magmatism remain poorly understood. Here, based on the recurrence of subduction earthquakes and the obtained surface heat flow estimates as constraints, we constructed a 3D thermodynamic model to study this subduction complex and the seismotectonic variation beneath Kermadec–Tonga. The subduction of the Pacific plate beneath the Kermadec–Tonga microplate is associated with a cold thermal transition from 300 °C to >900 °C on forearc interface. The distribution of seismicity is related to the dehydration of subducted water-bearing minerals which promotes the occurrence of both fast and slow subduction earthquakes. Slab metamorphism released large amounts of fluids, especially those from intraslab harzburgitization, which are key to influencing mantle melting and arc volcanism in Kermadec-Tonga.
... The external (applied) pressure p varied in the range of 0.1-10 GPa. This range particularly corresponds to tectonic plates at the characteristic depth interval from 3 km (upper crust) to 300 km (upper mantle) [20], or to highly stressed contact spots in heavily loaded tribological couples [67]. ...
... It is interesting to note that the point p 1 almost coincides with the pressure 2.7 GPa, at which a pressure-induced water insertion into kaolinite Al 2 Si 2 O 5 (OH) 4 ·3H 2 O (a layered hydroxide) is experimentally observed [20]. In this context, it is important that the formation of such a superhydrated phase of mineral may be related to the abrupt reversible increase in compressibility and the transition to a denser molecular packing of the nanoconfined water observed in our simulations (Figure 2a). ...
The interaction of water with confining surfaces is primarily governed by the wetting properties of the wall material—in particular, whether it is hydrophobic or hydrophilic. The hydrophobicity or hydrophilicity itself is determined primarily by the atomic structure and polarity of the surface groups. In the present work, we used molecular dynamics to study the structure and properties of nanoscale water layers confined between layered metal hydroxide surfaces with a brucite-like structure. The influence of the surface polarity of the confining material on the properties of nanoconfined water was studied in the pressure range of 0.1–10 GPa. This pressure range is relevant for many geodynamic phenomena, hydrocarbon recovery, contact spots of tribological systems, and heterogeneous materials under extreme mechanical loading. Two phase transitions were identified in water confined within 2 nm wide slit-shaped nanopores: (1) at p1 = 3.3–3.4 GPa, the liquid transforms to a solid phase with a hexagonal close-packed (HCP) crystal structure, and (2) at p2 = 6.7–7.1 GPa, a further transformation to face-centered cubic (FCC) crystals occurs. It was found that the behavior of the confined water radically changes when the partial charges (and, therefore, the surface polarity) are reduced. In this case, water transforms directly from the liquid phase to an FCC-like phase at 3.2–3.3 GPa. Numerical simulations enabled determination of the amount of hydrogen bonding and diffusivity of nanoconfined water, as well as the relationship between pressure and volumetric strain.
