H2O Oxygen Research Articles

In Situ TEM Study of the Degradation of PbSe Nanocrystals in Air

PbSe nanocrystals have attracted widespread attention due to a variety of potential applications. However, the practical utility of these nanocrystals has been hindered by their poor air stability, which induces undesired changes in the optical and electronic properties. An understanding of the degradation of PbSe nanocrystals when they are exposed to air is critical for improving the stability and enhancing their applications. Here, we use in situ transmission electron microscopy (TEM) with an environmental cell connected to air to study PbSe nanocrystal degradation triggered by air exposure. We have also conducted a series of complementary studies, including in situ environmental TEM study of PbSe nanocrystals exposed to pure oxygen and PbSe nanocrystals in H2O using a liquid cell, and ex situ experiments, such as O2 plasma treatment and thermal heating of PbSe nanocrystals under different air exposure. Our in situ observations reveal that when PbSe nanocrystals are exposed to air (or oxygen) under elec...

Applying the B12N12 nanoparticle as the CO, CO2, H2O and NH3 sensor

In this study, the various properties including the stability energies, structural and electronic aspects of the hydrazine (N2H4), carbon monoxide (CO) water (H2O) and ammonia (NH3) molecules adsorptions on the top of the boron nitride nanoparticles (BNn) were studied through the Minnesota Functionals computations, DFT/M06-2X. The calculations clarifies that the most stable adsorption configurations are those in which the oxygen, carbon, oxygen and nitrogen atoms of CO2, CO, H2O and NH3 are closed to the boron atom of the nanoparticle, respectively. The absorption energies were obtained about -0.14, -0.15, -0.87 and -1.54 eV for abosorption of CO2, CO, H2O and NH3 gasses. The geometry optimizations, energy calculations and NBO charge transfer were used to evaluate the sensing ability of BNn for different analytes. The computed density of states (DOS) clarifies that a strong orbital hybridization take place between CO2, CO, H2O and NH3 and BNn in adsorption process. Finally, it is concluded that the BNn nanoparticle has greater response selectivity toward NH3 compared to CO, CO2 and H2O

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Corrigendum.

Constraining magma storage conditions at a restless volcano in the Main Ethiopian Rift using phase equilibria models

The Main Ethiopian Rift hosts a number of peralkaline volcanic centres, several of which show signs of recent unrest. Due to the low number of historical eruptions recorded in the region and lack of volcanic monitoring, conditions of magma storage in the Main Ethiopian Rift remain poorly constrained. Aluto is one of these restless volcanic centres and identifying magma storage conditions is vital for evaluating the significance of recent periods of unrest. Using Aluto as a case study, we explore magma storage conditions using Rhyolite-MELTS thermodynamic modelling software. We performed ~150 fractional crystallisation models using a primitive basalt as the starting composition, and for a range of pressures (50–300MPa), initial H2O contents (0.5–3wt%) and oxygen fugacities (QFM−2–QFM+1). Predicted liquid lines of descent from these models are compared with published whole-rock data and, together with new observations of natural phase assemblages and erupted mineral compositions, provide constraints on magma storage conditions.Using a statistical approach to compare empirical data and thermodynamic model outputs, we find that compositions of evolved peralkaline rhyolites from Aluto are best reproduced by protracted (90%) isobaric fractional crystallisation from a rift-related basaltic composition, without the need for significant crustal assimilation. The required extent of fractional crystallisation suggests that much of the magmatic system may exist as a highly crystalline mush with only a small lens of rhyolitic melt. The best agreement between models and natural samples is at low pressures (150MPa), low initial H2O concentrations (0.5wt%) and an oxygen fugacity near the QFM buffer. The depth of magma storage derived from these results (~5.6±1km) is consistent with the source depths modelled from measured ground deformation. Data from other peralkaline volcanic centres in the Main Ethiopian Rift (Boset and Gedemsa), and other locations globally (e.g. Pantelleria, Italy) suggest that these storage conditions are a common feature of many peralkaline volcanic centres.

Theoretical Study of the Heterolytic σ Bond Cleavage on the Ge═O Bond of Germanone. An Insight into the Driving Force from Both Electronic and Dynamical Aspects.

The mechanism of the σ bond cleavage of H2O, NH3, Me2C═O, H2, CH4, BH3, and SiH4 on the Ge═O bond of germanone is examined by means of both quantum mechanical (QM) and molecular dynamics (MD) methods. The QM calculations show that the σ bonds of all the substrates are heterolytically broken on the very largely polarized Ge═O bond. Before the σ bond cleavage, the substrate at first approach the Ge═O germanium in the cases of H2O, Me2C═O, and NH3, and in contrast, the Ge═O oxygen in the cases of H2, CH4, BH3, and SiH4. For the cases of H2O, NH3, and Me2C═O, a cluster in which the substrate coordinates to the Ge exists before the σ bond cleavage, and this coordination of the substrate plays an important role on the heterolytic σ bond cleavage. The QM-MD simulations are also conducted for the case of H2O, and they show that the kinetic energy of the H2O-coordinated cluster especially concentrates on the coordinated H2O oxygen to strongly oscillate the coordinate bond between the H2O oxygen and the Ge. This oscillation further enlarges just before the O-H σ bond cleavage, and the kinetic energy of this oscillation would be transmitted to the normal mode of the O-H bond breaking. Thus, the coordination and the vibration of the H2O oxygen was thought to be an important driving force of the heterolytic cleavage of the O-H σ bond in both electronic and dynamical aspects.

Quantum Chemistry Calculations on the Mechanism of Isoquinoline Ring-Opening and Denitrogenation in Supercritical Water

Computational studies at the M06/6-311G(d,p) and M06-2X/6-311+G(d,p) levels were performed to explore the detailed mechanism of isoquinoline ring-opening and denitrogenation in a supercritical water system. Three reaction paths with the same product, 2-(2-oxoethyl) benzaldehyde, were supported by the computational results. The rate-limiting step in the major degradation reaction is an addition reaction at the N position. H2O is added to both the 1C–2N double bond (1C–2N addition reaction) and the 2N–3C double bond (2N–3C addition reaction) of the isoquinoline molecule, where the oxygen of H2O is added to the carbon atom. The energy barrier of the 1C–2N addition reaction is 52.7 kcal/mol, while that of 2N–3C addition (from Path 6) is 60.1 kcal/mol. From catalysis by two water molecules, the barrier of 1C–2N addition (Reaction (1)) is reduced to 27.5 kcal/mol. Catalysis from water molecule clusters is shown to considerably affect the process of isoquinoline ring-opening and denitrogenation, as indicated by ...

Electrochemical Oxygen Separation Using Layered Double Hydroxides As Hydroxide Ion Conductor

Oxygen separation membranes using oxide ion conducting materials have been studied for oxygen separation from air. However, the membrane can effectively separate oxygen from the air only at high temperatures higher than several hundred degrees, because the oxide ion conductor shows high ionic conductivity at only elevated temperatures. On the other hand, we have been studied layered double hydroxide (LDH) as a hydroxide ion conducting material [1-3]. LDHs are consisting of positively charged metal hydroxide layer and interlayer anions for charge compensation of cationic layer. The general formula for LDHs is [MII 1−x MIII x(OH)2][(An−)x/n • mH2O], where MII is a divalent cation such as Ni2+, Mg2+, Zn2+, etc., and MIII is a trivalent cation such as Al3+, Fe3+, Cr3+, etc., and An− is an anion such as CO3 2−, Cl−, OH−, etc. We have recently reported that LDHs intercalated with CO3 2- showed high ionic conductivity of the order of 10-3 S cm-1under humidification, and the LDHs are solid hydroxide ion conductors [1-3]. Here we report the development of an electrochemical oxygen separation process using a hydroxide ion conductor [4]. The electrochemical oxygen separation cell consists of pelletized OH− conductive solid electrolyte and electrodes. At the air feed side, oxygen in air, H2O and electrons produces OH- ions at the electrode with the electrochemical oxygen reduction reaction. At the same time, oxygen, H2O and electrons are generated from OH− ions at the other electrode with the electrochemical oxygen evolution reaction. Since H2O will easily be separated with O2, oxygen separation will be achieved. In this study, Ni-Fe LDH intercalated with CO3 2− (Ni-Fe CO3 2− LDH) was used as a hydroxide ion conductive material. The pellet of Ni-Fe CO3 2− LDH as an electrolyte was sandwiched with electrodes using Pt/C as a catalyst and Ni-Fe CO3 2− LDH as an ionomer. The oxygen concentration at the O2 product side was determined using a gas chromatography system. The electrochemical oxygen product flow was confirmed to be proportional to the external current density at 50oC under 70% of relative humidity, indicating that the membrane functioned as electrochemical oxygen separator. [1] K. Tadanaga, Y. Furukawa, A. Hayashi, M. Tatsumisago, Adv. Mater., 22 (2010) 4401-4404. [2] Y. Furukawa, K. Tadanaga, A. Hayashi, M. Tatsumisago, Solid State Ionics, 192(2011) 185-187. [3] D. Kubo, K. Tadanaga, A. Hayashi, M. Tatsumisago, J. Electroanal. Chem., 671 (2012) 102-105. [4] Y. Arishige, D. Kubo, K. Tadanaga, A. Hayashi, M. Tatsumisago, Solid State Ionics, 262 (2014) 238-240. Figure 1

Acetonitrile–water hydrogen-bonded interaction: Matrix-isolation infrared and ab initio computation

The 1:1 hydrogen-bonded complex of acetonitrile (CH3CN) and water (H2O) was trapped in Ar and N2 matrices and studied using infrared technique. Ab initio computations showed two types of complexes formed between CH3CN and H2O, a linear complex A with a CN⋯H interaction between nitrogen of CH3CN and hydrogen of H2O and a cyclic complex B, in which the interactions are between the hydrogen of CH3CN with oxygen of H2O and hydrogen of H2O with π cloud of CN of CH3CN. Vibrational wavenumber calculations revealed that both the complexes A and B were minima on the potential energy surface. Interaction energies computed at B3LYP/6-311++G(d,p) showed that linear complex A is more stable than cyclic complex B. Computations identified a blue shift of ∼11.5cm−1 and a red shift of ∼6.5cm−1 in the CN stretching mode for the complexes A and B, respectively. Experimentally, we observed a blue shift of ∼15.0 and ∼8.3cm−1 in N2 and Ar matrices, respectively, in the CN stretching mode of CH3CN, which supports the formation of complex A. The Onsager Self Consistent Reaction Field (SCRF) model was used to explain the influence of matrices on the complexes A and B. To understand the nature of the interactions, Atoms in Molecules (AIM) and Natural Bond Orbital (NBO) analyses were carried out for the complexes A and B.

Contrasting conditions of rift and off‐rift silicic magma origin on Iceland

AbstractFactors controlling the origin of silicic magmas on Iceland are poorly constrained. Here we present new data on H2O content, pressure, temperature, oxygen fugacity, and oxygen isotope composition of rhyolites from Askja, Öræfajökull, and Hekla volcanoes. All these parameters correlate with tectonic (rift and off‐rift) setting of the volcanoes. Askja rift rhyolites originate through extensive assimilation of high‐temperature hydrothermally altered crust (δ18O < 2‰) at shallow depths (≥1.8 km). These rhyolites are hot (935–1008°C), relatively dry (H2O < 2.7 wt%), and oxidized (QFM = +1.4). Cooler (874–902°C), wet (H2O = 4‐6.3 wt%), and non‐oxidized (~QFM to QFM‐1) off‐rift rhyolites (Öræfajökull, Hekla) originate through differentiation deeper in the crust (≥4 km) with almost no or little assimilation of high‐T, altered crust, as reflected by slightly lower to normal δ18O values (5.2–6‰). Although off‐rift rhyolites predominate during the Holocene, older silicic rocks on Iceland primarily formed in a rift setting possibly analogous to the oldest continental crust on Earth.

Sodium-promoted Pd/TiO2 for catalytic oxidation of formaldehyde at ambient temperature.

Catalytic oxidation of formaldehyde (HCHO) to CO2 at ambient conditions is of great interest for indoor HCHO purification. Here, we report that sodium-doped Pd/TiO2 is a highly effective catalyst for the catalytic oxidation of HCHO at room temperature. It was observed that Na doping has a dramatic promotion effect on the Pd/TiO2 catalyst and that nearly 100% HCHO conversion could be achieved over the 2Na-Pd/TiO2 catalyst at a GHSV of 95000 h(-1) and HCHO inlet concentration of 140 ppm at 25 °C. The mechanism of the Na-promotion effect was investigated by using Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), CO chemisorption, Temperature-programmed reduction by H2 (H2-TPR), X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption of O2 (O2-TPD) methods. The results showed that Na species addition can induce and further stabilize a negatively charged and well-dispersed Pd species, which then facilitates the activation of H2O and chemisorbed oxygen, therefore resulting in the high performance of the 2Na-Pd/TiO2 catalyst for the ambient HCHO destruction.

Water-Accelerated OH Addition to Sulfur Dioxide SO2: Direct Ab Initio Molecular Dynamics (AIMD) Study

Ionization dynamics of water microsolvated sulfur dioxide SO2(H2O)n (n = 1-3 and 6) have been investigated by means of direct ab initio molecular dynamics (AIMD) method to elucidate the hydration effects of OH addition reaction to SO2 following the ionization. The calculations showed that the neutral 1:1 complex SO2-H2O has a C(s) symmetry and the sulfur of SO2 interacts with the oxygen of H2O with an eclipsed form. In the case of ionization of SO2-H2O 1:1 complex (n = 1), the cation complex composed of [H2O-SO2](+) with a face-to-face form was obtained as the product. The OH addition reactions to SO2 were found in larger systems (n = 2, 3, and 6) following the ionization. The reaction was expressed as SO2(+)(H2O)n → SO2(OH)···H(+)(H2O)(n-1) (n = 2, 3, and 6). The proton generated as (SO2-H2O)(+) → (HSO3) + H(+) was stabilized by the second water molecule as the reaction: H(+) + H2O → H3O(+). These processes occurred and were completed within the cluster. The OH addition mechanism in SO2(+)(H2O)n cluster was discussed on the basis of the present results.

Silicate speciation in H2O–Na2O–SiO2 fluids from 3 to 40 mol% SiO2, to 600 °C and 2 GPa

The silicate speciation in H2O–Na2O–SiO2 fluids was studied in situ up to 600°C and 2.0GPa using Raman spectroscopy and a Bassett-type hydrothermal diamond-anvil cell. Fluid compositions ranged from 3 to 40mol% SiO2, with various Na/Si ratios. The main trends observed in Raman spectra of fluids with increasing SiO2 concentration include (1) decrease in the intensity of the ∼770cm−1 band (monomer, Q0, symmetric stretch); (2) increase in the intensity of the ∼1050cm−1 band (bridging oxygen Si–O–Si antisymmetric stretch) and the bands at ∼450–600cm−1 (bridging oxygen Si–O–Si bending modes); and (3) increase in spectral contributions at ∼800–1000cm−1 from stretching vibrations of Q1, Q2 and Q3 species. These trends are interpreted to represent decrease in the proportion of Q0 monomers, and increase in the proportions of Q1 and Q2 (±Q3) species, with increasing silicate concentration in the fluid up to 40mol% SiO2. Raman spectra in the range of tetrahedral Si–O stretching vibrations (700–1200cm−1) exhibit little discernable difference with changing Na/Si ratio, when compared at constant molar concentration of SiO2. Particularly at lower Na/Si ratio, increasing silicate concentration also results in increasing relative intensity of the Raman signal of O–H stretching vibrations at about 3300cm−1, suggesting increased intermolecular hydrogen bonding between H2O molecules and/or oxygen atoms belonging to silicate species. These results suggest that silicate in hydrous fluids in the deep Earth remains occurs predominately as partly polymerized, Q1 and Q2 species up to high silicate concentrations, providing an opportune medium for mobilizing high field-strength and other elements in the lithosphere.

Synthesis, characterization of dinuclear vanadium(III) hydroquinonate–iminodiacetate complexes

A new VIII complex (1) of 2,5-bis[N,N-bis(carboxymethyl)aminomethyl]hydroquinone (bicah6−) was synthesized by reaction of H6bicah with two equivalents of VCl3 and six equivalents of base in aqueous solution. Crystallographic characterization shows the neutral complex to have a dinuclear hydroquinonate bridged structure. The octahedral environment of vanadium is occupied by the four (N, O, O, O) donor atoms in each binding site of the ligand and two H2O oxygen atoms. Addition of 2,2-bipyridine (bipy) in the reaction mixture resulted in the synthesis of a new dinuclear VIII-μ-bicah6− complex (2) containing a bipy chelated to each vanadium center. The structure of 1 was compared with the respective dinuclear structures of the bicah6− complexes with VIVO2+ (3) and VVO2+ (4). Strong hydrogen bonds between the free, the ligated to vanadium water molecules and the carboxylate and hydroquinonate oxygen atoms result in supramolecular 3D structures by self-assembly of the dinuclear units. These structures are controlled by synthesis conditions and vanadium ion coordination environment. The cyclic voltammogram of 1 showed a reversible VIV+e-⇋VIII process at 0.48V versus NHE. The EPR spectra of 3 gave a broad peak indicating magnetic interactions between the uncoupled electrons of the two vanadium centers through the hydroquinone bridge. In acidic pHs bellow 2.0, EPR data reveal protonation of the hydroquinonate oxygen and hydrolysis of the complex. The relation of these results with the reduction of VIV and stabilization of VIII ions is discussed.

Adsorption of atmospheric oxidants at divacancy sites of graphene: A DFT study

Periodic DFT calculations are performed to compare the reactivity with respect to atmospheric oxidants like O2, H2O, O3 and atomic oxygen of different divacancy structures created in graphene sheet by removing two adjacent carbon atoms. The present approach shows that O and O3 can easily be chemisorbed at the divacancy sites, the reaction product being however strongly dependent on the divacancy structure. The situation appears more intricate when considering the interaction of O2 and H2O with the defective graphene sheet. In this case, dissociative chemisorption on the surface is evidenced only when dangling bonds are present at the divacancy site.

Fundamental studies about the interaction of water with perfect, oxygen-vacancy and pre-covered oxygen Cu2O(1 1 1) surfaces: Thermochemistry, barrier, product

The adsorption and dissociation of H2O on three types of Cu2O(111) surfaces, including perfect, oxygen-vacancy and pre-covered oxygen surfaces have been systematically investigated using periodic density functional slab model calculations. Different kinds of possible modes of H2O adsorbed on those surfaces are identified. Our results first show that the bonding of dissociated species (HO, H and O) for H2O is substantially stronger than that of H2O on Cu2O(111) surface. Then, on perfect surface, H2O mainly exist in the form of molecular adsorption, in which CuCUS site is chemisorption, OSUF site is physisorption with a weak hydrogen bond. On oxygen-vacancy surface, dissociative adsorption of H2O occurs predominantly, suggesting that oxygen-vacancy exhibits a strong catalytic activity toward H2O dissociation; meanwhile, a small quantity of chemisorption H2O adsorbed at CuCUS site also exists. On pre-covered oxygen surface, H2O is typical of physisorption due to a hydrogen bond interaction between H of adsorbed H2O and pre-covered oxygen. Further, the dissociation mechanisms of molecular adsorption H2O, OH from dissociative adsorption H2O, as well as single OH group on different surfaces, leading to the final products H and O atoms, give out the thermochemistry, barrier of each elementary reaction, which indicates that OH species is energetically the most stable product on those surfaces. Pre-covered oxygen on Cu2O(111) surface can act as a promoter to facilitate the first dehydrogenation of molecular adsorption H2O leading to OH species, which is more favorable both thermodynamically and kinetically than that of molecular adsorption H2O on other two surfaces. Finally, the vibrational frequencies for the adsorbed H2O and OH species on Cu2O(111) surfaces can be applied to guide surface vibrational spectroscopy in experiment. Our calculation may be a worthwhile theoretical example for the interaction of H2O with other metal oxide surface.

A new solid oxide molybdenum–air redox battery

A new type of rechargeable molybdenum–air battery based on the technologies of reversible solid oxide fuel cells and chemical looping is reported in this study. The reversible solid oxide fuel cell serves as the electrical unit to realize the charging and discharging cycles while a pair of Mo/MoO2 redox couple integrated with the reversible solid oxide fuel cell stores electrical energy via an H2–H2O oxygen shuttle. The specific charge of the new battery reaches 1117 A h per kg-Mo at 550 °C, which is 45% higher than the non-rechargeable Mo–air battery. The corresponding discharge specific energy is 974 W h per kg-Mo with a round trip efficiency of 61.7%. In addition, the new Mo–air redox battery also exhibits 13.9% and 24.5% higher charge density (A h L−1) and energy density (W h L−1) than the state-of-the-art solid oxide Fe–air redox battery, respectively.

No oxygen isotope exchange between water and APS–sulfate at surface temperature: Evidence from quantum chemical modeling and triple-oxygen isotope experiments

In both laboratory experiments and natural environments where microbial dissimilatory sulfate reduction (MDSR) occurs in a closed system, the δ34SSO4 ((34S/32S)sample/(34S/32S)standard−1) for dissolved SO42− has been found to follow a typical Rayleigh-Distillation path. In contrast, the corresponding δ18OSO4 ((18O/16O)sample/(18O/16O)standard)−1) is seen to plateau with an apparent enrichment of between 23‰ and 29‰ relative to that of ambient water under surface conditions. This apparent steady-state in the observed difference between δ18OSO4 and δ18OH2O can be attributed to any of these three steps: (1) the formation of adenosine-5′-phosphosulfate (APS) from ATP and SO42−, (2) oxygen exchange between sulfite (or other downstream sulfoxy-anions) and water later in the MDSR reaction chain and its back reaction to APS and sulfate, and (3) the re-oxidation of produced H2S or precursor sulfoxy-anions to sulfate in environments containing Fe(III) or O2. This study examines the first step as a potential pathway for water oxygen incorporation into sulfate. We examined the structures and process of APS formation using B3LYP/6-31G(d,p) hybrid density functional theory, implemented in the Gaussian-03 program suite, to predict the potential for oxygen exchange. We conducted a set of in vitro, enzyme-catalyzed, APS formation experiments (with no further reduction to sulfite) to determine the degree of oxygen isotope exchange between the APS–sulfate and water. Triple-oxygen-isotope labeled water was used in the reactor solutions to monitor oxygen isotope exchange between water and APS sulfate.The formation and hydrolysis of APS were identified as potential steps for oxygen exchange with water to occur. Quantum chemical modeling indicates that the combination of sulfate with ATP has effects on bond strength and symmetry of the sulfate. However, these small effects impart little influence on the integrity of the SO42− tetrahedron due to the high activation energy required for hydrolysis of SO42− (48.94kcal/mol). Modeling also indicates that APS dissociation via hydrolysis is achieved through cleavage of the P–O bond instead of S–O bond, further supporting the lack of APS–H2O–oxygen exchange. The formation of APS in our in vitro experiments was verified by HPLC fluorescence spectroscopy, and triple-oxygen isotope data of the APS–sulfate indicate no oxygen isotope exchange occurred between APS–sulfate and water at 30°C for an experimental duration ranging from 2 to 120h. The study excludes APS formation as one of the causes for sulfate–oxygen isotope exchange with water during MDSR.

Case Scenario

Case Scenario

Syntheses, structure and photoluminescent properties of lanthanide oxalatosulfocarboxylate coordination polymers

Hydrothermal reactions of oxalic acid (H2ox) and 2-sulfobenzoic acid (H2L) with lanthanide oxide or hydroxide yielded five lanthanide oxalatosulfocarboxylates. They have a general formula [Ln2L2(ox)(H2O)6]n [Ln = La (1), Nd (2), Eu (3), Gd (4), Tb (5)]. Their structures were characterized by single crystal X-ray diffraction, powder X-ray diffraction (PXRD), infrared (IR) spectroscopy, elemental analysis (EA), and thermogravimetric analysis (TGA). 1–5 are isostructural coordination polymers and feature one-dimensional (1D) chains, which are extended into 3D supramolecular frameworks through inter-chain hydrogen bonds between coordinated H2O donors and oxygen acceptors from carboxylate, sulfonate and oxalate groups. In addition, the solid-state photoluminescence properties of the Nd (2), Eu (3) and Tb (5) derivatives have been measured at room temperature. The Eu and Tb-containing coordination polymers (CPs) exhibit intense red and green luminescence emissions, respectively, with lifetimes in the order of millisecond.

Initiation and development of the Twelve Mile Bay shear zone: the low viscosity sole of a granulite nappe

Structural, microstructural and petrological data have enabled determination of the mechanical and geochemical processes involved in dynamic weakening and fabric transposition along the margins of a granulite nappe (the Parry Sound domain (PSD)) during transport to mid-crustal levels of the Grenville Orogen. The data establish a genetic link between outcrop-scale structures in the southern PSD and the development of the underlying Twelve Mile Bay shear zone (TMBSZ). Following granulite facies metamorphism (� 11 kbar ⁄ � 850 � C) in the southern PSD, the emplacement of pegmatite dykes resulted in hydration reactions within adjacent wall rocks and the development of thin (<1 m) amphibolite facies (� 6.5 kbar ⁄ � 700 � C) shear zones. The shear zones exhibit bulk H2O and K2O enrichment and oxygen isotope values similar to the adjacent pegmatites, suggesting metasomatic alteration by pegmatite-derived fluids. Phase-equilibrium models indicate that the destabilization of the pre-existing pyroxene and garnet-bearing assemblages, as observed within discrete shear zones in the southern PSD and the TMBSZ, requires H2O-saturated conditions at these (amphibolite facies) P-T conditions. The spacing between discrete shear zones and the depth of hydration into the adjacent wall rock are of comparable length-scales (� metres), suggesting that this type of reworking process can be an effective means of hydrating kilometre-scale areas of crust relatively rapidly. Furthermore, considering the well- established effects of hydrous fluids on the creep strength of anhydrous minerals, a fracture-initiated, localized hydration-and-shearing process may be an efficient mechanism for weakening strong, dry rocks (e.g. granulites) in the middle to lower orogenic crust.