Boundary Of Transition Zone Research Articles

A transition zone boundary determining method based on MIKE21: A case study of Baiyangdian Lake, North China

River and lake ecosystems converge to form transition zones, which play a key role in the flow of organisms, matter and energy. Although the importance of transition zone has been gradually recognized, there is still a lack of unified understanding on the transition zone boundary determination. In this study, taking Baiyangdian Lake, North China as an example, we proposed a method for determining the transition zone boundary based on water quality gradient using MIKE21 software, in which the confluence of the river and the lake was taken as the upper boundary, and the lower boundary was determined according to the variation inflection point of the water quality gradient. Total nitrogen (TN) was selected as the critical parameter due to its key role and high percentage among inflow river pollution. The results showed that the transition zone ranges varied with inflow rates and TN concentrations, as well landforms, and the corresponding areas of three transition zones, namely Fu River-Baiyangdian Lake, Xiaoyi River-Baiyangdian Lake and Baigou Canal-Baiyangdian Lake were 37.92, 34.11 and 24.99 km2 under critical flow conditions respectively. And the transition zone boundary was stable when connected flow was higher than critical value. This study has explored a theoretical way of determining the boundary of the river–lake transition zones, thus providing a scientific basis for further research on water quality-ecological response and the optimal allocation of water resources in transition zone.

Constraining seismic anisotropy on the mantle transition zone boundaries beneath the subducting Nazca slab

Some seismic evidence suggests that the mantle transition zone (MTZ) may become highly hydrous and anisotropic, particularly in the vicinity of subduction zones. The two-dimensional path-integrated anisotropy from the upper mantle to the MTZ has been well established beneath the northwestern region of South America. However, explicit details of azimuthal anisotropy on the MTZ boundaries remains ambiguous. Therefore, we attempted to constrain the azimuthal anisotropy on the MTZ boundaries by implementing the P-to-S anisotropic receiver function analysis. We detected significant seismic evidence of azimuthal anisotropy on the 410-km discontinuity, but weak anisotropy on the 660-km discontinuity. The synthetic waveform modeling indicated the fast symmetry axis of anisotropy trends 50° from the north and plunges 40° downwards from horizontal with an anisotropy strength of 4.0% near 410 km depth. The direction of anisotropy suggests the mantle material moves downwards and towards the subducting Nazca slab near the depth of 410 km. The increased anisotropy strength around the 410 km suggests the hydrous wadsleyite may attribute to anisotropy in the upper MTZ. The lack of detectable seismic anisotropy near the depth of 660 km could be caused by the insufficient amount of aligned anisotropic minerals, even though the mantle material continues moving downwards.

A Method for Computing Slip-Line Fields with Stress Discontinuity in Cohesionless Backfills

A method for computing slip-line fields in the case of cohesionless backfills with stress discontinuity was proposed. The potential failure zone is divided into the Rankine zone and the transition zone, and the Rankine zone is rigorously determined using the theory of plastic mechanics. The potential failure zone and the Rankine zone are then further divided into a series of triangular slices. On the basis of the force and moment equilibrium conditions of a typical triangular slice, the recurrence equation of the lateral force is established. Furthermore, the relationship between the failure surface inclination angle and the interslice force inclination angle is established by satisfying the Mohr–Coulomb criterion. An iterative procedure for calculating the lateral force of the triangular slices by changing the failure surface inclination in the transition zone is performed until the interslice force satisfies the stress condition of the transition zone boundary, resulting in a stress discontinuity line if the Rankine zone and the transition zone intersect and the intersection line satisfies the stress characteristics of stress discontinuity. Example studies are performed to verify the present method, which shows that the soil–wall interface friction has the most significant effect on stress discontinuity, and the location of the stress discontinuity line gradually approaches the backfill surface with an increase in retaining wall inclination.

Engineering properties of waste-based alkali activated concrete brick containing low calcium fly ash and rice husk ash: A comparison with traditional Portland cement concrete brick

Alkali activated concrete bricks manufactured from waste materials are an alternative to replace PC as the principal binder in brick manufacture. The current study reports the mechanical and durability properties of blended fly ash and 20% rice husk ash (20RHA) alkali activated bricks and compares with Portland cement (PC) bricks (100PC). The 20RHA brick showed a compressive strength growth rate of 4% between 7 and 28 days as compared to 13.8% for 100PC bricks. Both achieved similar 28 days compressive strength (approximately 17 MPa). High tensile strength was observed in 20RHA this is attributed to the high bond strength at the interface of the 20RHA alkali activated binder and aggregates. In microstructural investigation, 20RHA brick displayed a stronger bond within the interfacial transition zone (ITZ) boundary compared to 100PC bricks at all ages. This makes the fracture plane more prone to pass through the aggregates than through the bond interface. Lower capillary suction near the surface for 20RHA concrete is hypothesized as the reason for the lower initial rate of absorption obtained for 20RHA when compared with 100PC. The addition of RHA makes the bricks more vulnerable to efflorescence when exposed to moisture due to the combined effect of the high porosity, a high Na2O/Al2O3 ratio and greater leaching of sodium ions.

Long term mechanical performance of nano-engineered high volume fly ash concrete

High Volume Fly Ash (HVFA) concrete is a sustainable construction material which can act as a viable alternative to Portland cement (PC) concrete. This study investigates the long-term mechanical performance of two unique HVFA concrete mixes, 65% and 80% cement replacements, incorporating hydrated lime, up to 18%, and 3% nano silica. HVFA-65 concrete achieved compressive strength values increasing from 32 to 73 MPa, from 7 to 450 day while HVFA-80 displayed a strength increase from 22 to 71 MPa in the same period. The flexural strength of HVFA-65 concrete increased from 3.6 to 8.7 MPa while the splitting tensile strength and elastic modulus gave values of 2.7–5.8 MPa and 30.3–40.5 GPa, respectively. Meanwhile, HVFA-80 concrete achieved flexural strengths of 2.7–8.7 MPa, splitting tensile strengths of 1.6–5.0 MPa and an elastic modulus of 28.9–37.0 GPa. Analysis of paste samples identified the presence of 11%, 3.2%, 5.3% and 2.1% higher concentrations of Portlandite within the HVFA-65 system at 7, 28, 90 and 450 days respectively, indicating a high availability of portlandite for the pozzolanic reaction of the fly ash. In microstructural investigation, HVFA-65 concrete displayed a denser gel matrix and stronger bond within the interfacial transition zone (ITZ) boundary compared to HVFA-80 at all ages. In addition, a statistical regression analysis conducted to predict relationships between long term mechanical properties of HVFA concrete are compared with existing design equations available in Australian Standards and ACI codes.

A new data‐driven riparian revegetation design method

AbstractHydrologic and physical gradients influence vegetation zonation and can form the basis of riparian revegetation design. We present a new data‐driven method to develop riparian revegetation designs by relating the ground height above river (HAR) or a low streamflow water surface as a groundwater proxy to existing vegetation cover types and applying those relationships to design conditions. Steps in the process are as follows: (1) map existing vegetation within the riparian corridor; (2) construct existing and design topographic and groundwater digital elevation models (DEMs), and then difference those DEMs to create a HAR detrended DEM (HAR dtDEM); (3) define existing vegetation habitat zones using the relationship between existing HAR dtDEM and mapped vegetation cover types; (4) apply habitat zone boundaries to detrended design topography; and (5) develop planting schematics using habitat zones and detrended design topography. We developed a revegetation design for a rehabilitation site on the Trinity River, California, using the HAR dtDEM method. We used a data‐driven method to define five habitat zones in riparian areas: aquatic, emergent margin, mesic, mesic–xeric transition, and xeric zones. Zonal boundaries were identified using four criteria: (1) capillary fringe elevation above the low flow water surface, (2) shifts from herbaceous to woody‐dominated cover types, (3) a difference equal to or >0.5 m between two adjacent ranked cover types, and (4) locations where a linear trendline intersected median HAR values or where a group of regression residuals changed from positive to negative or vice versa. The capillary fringe height was the most effective method when determining vegetation zones near the channel. The shift between herbaceous and woody‐dominated cover types defined the boundary between the emergent margin and mesic zone. Elevation increases >0.5 m between adjacent ranked cover types defined the upper and lower mesic–xeric transition zone boundaries best. Comparing linear residuals was most useful for separating drier cover types occurring on higher ground surfaces. Existing habitat zone boundaries were applied to detrended design topography to direct which selected native plant species could be arranged within habitat zones to improve planting survival and increase ecological function following rehabilitation.

Localized Anisotropy in the Mantle Transition Zone Due to Flow Through Slab Gaps

AbstractMeasurement of anisotropy advances our understanding of mantle dynamics by linking remote seismic observations to local deformation state through constraints from mineral physics. The Pacific Northwest records the largest depth‐integrated anisotropic signals across the western United States but the depths contributing to the total signal are unclear. We used the amplitudes of orthogonally polarized P‐to‐S converted phases from the mantle transition zone boundaries to identify anisotropy within the ∼400–700 km deep layer. Significant anisotropy is found near slab gaps imaged by prior tomography. Focusing of mantle flow through slab gaps may lead to locally elevated stress that enhances lattice preferred orientation of anisotropic minerals within the transition zone, such as wadsleyite.

A Critical Note on the Engineering Model of Radiating Antenna in Homogeneous Medium: Field Regions and Transition Zone Boundaries

Although radiating antenna field configuration and propagation principles in homogeneous media were theoretically established long ago, certain issues in their practical implementation proved full of twists and turns due to the complexity of the physical processes and mathematical intricacies. Those may and often do result in confusion with multiple definitions of antenna near and far field regions and the various “rules of thumb” criteria for their boundaries, contradicting each other to the frustration of practicing engineers. This may lead to erroneous interpretation of measurement results as well as technical difficulties and financial losses in important practical applications. The purpose of this work is to address this kind of issues regarding the formulation and implementation of the engineering model of the radiating antenna field. Based on the well established physical and mathematical underpinnings we elucidate the origins of and physical mechanisms behind the arising problems, as well as their potential effect on development of modern technologies. We also look at ideas for potential improvements and standardization in these areas.

Mantle Transition Zone Structure Beneath Myanmar and Its Geodynamic Implications

AbstractLinking the India‐Tibet collision to the north and the Andaman oceanic subduction to the south, Myanmar occupies a crucial position in the India‐Eurasia convergence system. Various seismological studies have indicated that the Indian plate is obliquely subducted along the Burma arc. However, the depth extent and continuity of the subducted slab remain enigmatic. With seismic recordings collected from 114 recently deployed seismic stations, we map the topographies of the mantle transition zone (MTZ) boundaries, that is, the 410‐ and 660‐km discontinuities, beneath Myanmar using receiver functions. Regional 3‐D velocity models were adopted to account for the lateral velocity heterogeneity. The 410‐km discontinuity is uplifted by over 15 km within 95°E‐97°E and 21°N‐24°N beneath Myanmar. This feature correlates well with the east‐dipping high‐velocity anomaly in the tomographic models, with a velocity increase of 0.9%–1.2% at the 410‐km discontinuity depth, suggesting that the subducted slab has reached the MTZ. The uplift of the 410‐km discontinuity terminates to the south at ∼21°N, indicating a distinct change in slab geometry. Our results also reveal a depressed 660‐km discontinuity, which is spatially offset to the southwest of the uplifted 410‐km discontinuity. We propose that the offset between the 410‐km discontinuity uplift and the 660‐km discontinuity depression could indicate a slab break‐off and tearing beneath Myanmar, which was triggered by the northward motion of the Indian plate during the eastward subduction. We further speculate that the slab tear could mark the transition from oceanic to continental plate subduction.

Root Development: A Go-Faster Stripe and Spoilers.

Root growth depends on spatially distinct cell division and elongation activities in the root meristem. The correct positioning of a "transition zone" boundary between the division and elongation zones is critical for efficient root growth; new work from Salvi etal. sheds light on how this boundary is established and maintained.

A Mississippian black shale record of redox oscillation in the Craven Basin, UK

Early diagenetic redox oscillation processes have been rarely recognised in the ancient rock record but potentially exert an important control on mineral authigenesis, hydrocarbon prospectivity and supply of metals and/or reduced S as part of associated mineral systems. The upper unit of the Mississippian Bowland Shale Formation is a candidate record of diagenetic redox oscillation processes because it was deposited under a relatively high sediment accumulation rate linked to a large delta system, and under dominantly anoxic and intermittently sulphidic bottom-water conditions. In order to characterise the syngenetic and early diagenetic processes, sedimentological and geochemical data were integrated through the Upper Bowland Shale at three sites in the Craven Basin (Lancashire, UK). Organic matter (OM) comprises a mixture of Type II, II-S, II/III and III OM. ‘Redox zones’ are defined by patterns of Fe-speciation and redox-sensitive trace element enrichment and split into two groups. ‘Sulphidic’ zones (EUX, AN-III, AN-I and AN-IT) represent sediments deposited under conditions of at least intermittently active sulphate-reduction in bottom-waters. ‘Non-sulphidic’ zones (OX-RX, OX-F and OX) represent sediments deposited under non-sulphidic (oxic to ferruginous anoxic) bottom-waters. Operation of a shelf-to-basin ‘reactive Fe’ (FeHR) shuttle, moderated by sea level fluctuation and delta proximity, controlled the position and stability of redoxclines between zones of Fe and sulphate reduction, and methanogenesis. Early diagenetic redoxclines were capable of migration through the shallow sediment column relatively quickly, in response to sea level fluctuation. Preservation of syngenetic and early diagenetic geochemical signals shows redoxclines between Fe and sulphate reduction, and the upper boundary of sulphate-methane transition zone, were positioned within decimetres (i.e., 10 s cm) of seabed. Falling sea level and increasing FeHR supply is recognised as a switch from zones EUX (high sea level), AN-III and ultimately AN-I and AN-IT (low sea level). Zone AN-I defines the operation of ‘redox oscillation’, between zones of Fe and sulphate reduction in shallow porewaters, associated with enhanced degradation of OM and complete dissolution of primary carbonate. Preservation of OM and carbonate, in this system, was a function of changing bottom and pore water redox processes. Redox oscillation operated in a siliciclastic, prodeltaic environment associated with a relatively high sediment accumulation rate and high loadings of labile organic matter and metal oxides. These findings are important for understanding Late Palaeozoic black shales in the context of hydrocarbon and mineral systems.

The role of water in Earth's mantle.

Geophysical observations suggest that the transition zone is wet locally. Continental and oceanic sediment components together with the basaltic and peridotitic components might be transported and accumulated in the transition zone. Low-velocity anomalies at the upper mantle–transition zone boundary might be caused by the existence of dense hydrous magmas. Water can be carried farther into the lower mantle by the slabs. The anomalous Q and shear wave regions locating at the uppermost part of the lower mantle could be caused by the existence of fluid or wet magmas in this region because of the water-solubility contrast between the minerals in the transition zone and those in the lower mantle. δ-H solid solution AlO2H–MgSiO4H2 carries water into the lower mantle. Hydrogen-bond symmetrization exists in high-pressure hydrous phases and thus they are stable at the high pressures of the lower mantle. Thus, the δ-H solid solution in subducting slabs carries water farther into the bottom of the lower mantle. Pyrite FeO2Hx is formed due to a reaction between the core and hydrated slabs. This phase could be a candidate for the anomalous regions at the core–mantle boundary.

Deformable plate tectonic models of the southern North Atlantic

Significant, poly-phase deformation occurred prior to, simultaneous with, and after the opening of the North Atlantic Ocean. Understanding this deformation history is essential for understanding the regional development and the mechanisms controlling rifting and subsequent failure or breakup. Here, we primarily use published constraints to construct deformable plate tectonic models for the southern North Atlantic from 200 Ma to present using GPlates. The aim of this work is to test both the capability of the GPlates deformable modelling approach and the reliability of published plate reconstructions. Overall, modelled crustal thickness values at 0 Ma produced from the deformable models show general, regional-scale, similarities with values derived from the inversion of gravity data for crustal thickness. However, the deformable models typically underestimate thinning in marginal basins and overestimate crustal thickness in continental fragments compared to values from gravity inversion. This is possibly due to: 1) thinning occurring earlier than the 200 Ma start time modelled, 2) variations in the original crustal thickness, 3) depth-dependent stretching, 4) rigid blocks undergoing some degree of thinning, and 5) variations in the mesh density of the models. The results demonstrate that inclusion of micro-continental fragments, and locally defined limits of continental crust, generally produce results more akin to observations. One exception is the Grand Banks where global GPlates models produce more realistic deformation, likely due to the inclusion of the exhumed domains continent-ward of the transition zone boundary. Results also indicate that Flemish Cap rotation is required to provide a reasonable fit between North America and Iberia, with the palaeo-position of the Flemish Cap likely to be the proto-Orphan sub-basins. Moreover, the East and West Orphan sub-basins formed separately due to the respective rotations of the Flemish Cap and the Orphan Knoll, which was likely associated with other continental fragments that subsequently contributed to the thicker crust forming the boundary between the East and West Orphan basins. The results also suggest a link between tectonic and magmatic processes. For example, the inclusion of an Orphan Knoll micro-continental block results in greater extension (higher beta factors) in the northern West Orphan Basin near the termination of the Charlie-Gibbs Fracture Zone, and the site of the Charlie-Gibbs Volcanic Province (CGVP). Thus, we infer that the CGVP was likely influenced by plate tectonic processes through the concentration of strain resulting from interaction in proximity to the transform system. Finally, marginal basins that were considered to be conjugate and thus related, may only appear conjugate through later rotation of micro-continental blocks, and thus their genesis is not directly related.

Mineral inclusions in diamonds from Karowe Mine, Botswana: super-deep sources for super-sized diamonds?

Mineral inclusions in diamonds play a critical role in constraining the relationship between diamonds and mantle lithologies. Here we report the first major and trace element study of mineral inclusions in diamonds from the Karowe Mine in north-east Botswana, along the western edge of the Zimbabwe Craton. From a total of 107 diamonds, 134 silicate, 15 oxide, and 22 sulphide inclusions were recovered. The results reveal that 53% of Karowe inclusion-bearing diamonds derived from eclogitic sources, 44% are peridotitic, 2% have a sublithospheric origin, and 1% are websteritic. The dominant eclogitic diamond substrates sampled at Karowe are compositionally heterogeneous, as reflected in wide ranges in the CaO contents (4–16 wt%) of garnets and the Mg# (69–92) and jadeite contents (14–48 mol%) of clinopyroxenes. Calculated bulk rock REEN patterns indicate that both shallow and deep levels of the subducted slab(s) were sampled, including cumulate-like protoliths. Peridotitic garnet compositions largely derive from harzburgite/dunite substrates (~90%), with almost half the garnets having CaO contents <1.8 wt%, consistent with pyroxene-free (dunitic) sources. The highly depleted character of the peridotitic diamond substrates is further documented by the high mean and median Mg# (93.1) of olivine inclusions. One low-Ca garnet records a very high Cr2O3 content (14.7 wt%), implying that highly depleted cratonic lithosphere at the time of diamond formation extended to at least 220 km depth. Inclusion geothermobarometry indicates that the formation of peridotitic diamonds occurred along a 39–40 mW/m2 model geotherm. A sublithospheric inclusion suite is established by three eclogitic garnets containing a majorite component, a feature so far unique within the Orapa cluster. These low- and high-Ca majoritic garnets follow pyroxenitic and eclogitic trends of majoritic substitution, respectively. The origin of the majorite-bearing diamonds is estimated to be between 330 to 420 km depth, straddling the asthenosphere–transition zone boundary. This new observation of superdeep mineral inclusions in Karowe diamonds is consistent with a sublithospheric origin for the exceptionally large diamonds from this mine.

Encapsulating Earth's deep water filter

Geochemistry Small inclusions in diamonds brought up from the mantle provide valuable clues to the mineralogy and chemistry of parts of Earth that we cannot otherwise sample. Tschauner et al. found inclusions of the high-pressure form of water called ice-VII in diamonds sourced from between 410 and 660 km depth, the part of the mantle known as the transition zone. The transition zone is a region where the stable minerals have high water storage capacity. The inclusions suggest that local aqueous pockets form at the transition zone boundary owing to the release of chemically bound water as rock cycles in and out of this region. Science , this issue p. [1136][1] [1]: /lookup/doi/10.1126/science.aao3030

Ice-VII inclusions in diamonds: Evidence for aqueous fluid in Earth's deep mantle.

Water-rich regions in Earth's deeper mantle are suspected to play a key role in the global water budget and the mobility of heat-generating elements. We show that ice-VII occurs as inclusions in natural diamond and serves as an indicator for such water-rich regions. Ice-VII, the residue of aqueous fluid present during growth of diamond, crystallizes upon ascent of the host diamonds but remains at pressures as high as 24 gigapascals; it is now recognized as a mineral by the International Mineralogical Association. In particular, ice-VII in diamonds points toward fluid-rich locations in the upper transition zone and around the 660-kilometer boundary.

A Bayesian method to quantify azimuthal anisotropy model uncertainties: application to global azimuthal anisotropy in the upper mantle and transition zone

Seismic anisotropy is a powerful tool to constrain mantle deformation, but its existence in the deep upper mantle and topmost lower mantle is still uncertain. Recent results from higher mode Rayleigh waves have, however, revealed the presence of 1% azimuthal anisotropy between 300 km and 800 km depth, and changes in azimuthal anisotropy across the mantle transition zone boundaries. This has important consequences for our understanding of mantle convection patterns and deformation of deep mantle material. Here, we propose a Bayesian method to model depth variations in azimuthal anisotropy and to obtain quantitative uncertainties on the fast seismic direction and anisotropy amplitude from phase velocity dispersion maps. We applied this new method to existing global fundamental and higher mode Rayleigh wave phase velocity maps to assess the likelihood of azimuthal anisotropy in the deep upper mantle and to determine whether previously detected changes in anisotropy at the transition zone boundaries are robustly constrained by those data. Our results confirm that deep upper mantle azimuthal anisotropy is favored and well-constrained by the higher mode data employed. The fast seismic directions are in agreement with our previously published model. The data favor a model characterized, on average, by changes in azimuthal anisotropy at the top and bottom of the transition zone. However, this change in fast axes is not a global feature as there are regions of the model where the azimuthal anisotropy direction is unlikely to change across depths in the deep upper mantle. We were, however, unable to detect any clear pattern or connection with surface tectonics. Future studies will be needed to further improve the lateral resolution of this type of model at transition zone depths

Seismic evidence for water transport out of the mantle transition zone beneath the European Alps

The mantle transition zone has been considered a major water reservoir in the deep Earth. Mass transfer across the transition-zone boundaries may transport water-rich minerals from the transition zone into the water-poor upper or lower mantle. Water release in the mantle surrounding the transition zone could cause dehydration melting and produce seismic low-velocity anomalies if some conditions are met. Therefore, seismic observations of low-velocity layers surrounding the transition zone could provide clues of water circulation at mid-mantle depths. Below the Alpine orogen, a depressed 660-km discontinuity has been imaged clearly using seismic tomography and receiver functions, suggesting downwellings of materials from the transition zone. Multitaper-correlation receiver functions show prominent ∼0.5–1.5% velocity reductions at ∼750–800-km depths, possibly caused by partial melting in the upper part of lower mantle. The gap between the depressed 660-km discontinuity and the low-velocity layers is consistent with metallic iron as a minor phase in the topmost lower mantle reported by laboratory studies. Velocity drops atop the 410-km discontinuity are observed surrounding the Alpine orogeny, suggesting upwelling of water-rich rock from the transition zone in response to the downwelled materials below the orogeny. Our results provide evidence that convective penetration of the mantle transition zone pushes hydrated minerals both upward and downward to add hydrogen to the surrounding mantle.

Experimental Investigation of the Supersonic Flow over an Axisymmetric Ring Cavity

This paper presents the results of the experimental investigation of the supersonic flow over a ring cavity of rectangular cross-section on a cylindrical body with a conical tip. The evolution of the flow over a cavity with its continuously changing extent has been investigated. The transition zone boundaries within which both an open and a closed schemes of flow are possible have been determined by the parameter of the relative extent of the cavity. It has been shown that the flow conditions in the transition zone depend on the prehistory of the flow. The main stages of cavity flow restricuting at the transition zone boundaries have been described.

Water and partial melting of Earth’s mantle

Abstract Water plays a crucial role in the melting of Earth’s mantle. Mantle magmatisms mostly occur at plate boundaries (including subduction zones and mid-ocean ridges) and in some intraplate regions with thermal anomaly. At oceanic subduction zones, water released by the subducted slab may induce melting of the overlying mantle wedge or even the slab itself, giving rise to arc magmatism, or may evolve into a supercritical fluid. The physicochemical conditions for the formation of slab melt and supercritical fluid are still under debate. At mid-ocean ridges and intraplate hot zones, water and CO2 cause melting of the upwelling mantle to occur at greater depths and in greater extents. Low degree melting of the mantle may occur at boundaries between Earth’s internal spheres, including the lithosphere-asthenosphere boundary (LAB), the upper mantle- transition zone boundary, and the transition zone-lower mantle boundary, usually attributed to contrasting water storage capacity across the boundary. The origin for the stimulating effect of water on melting lies in that water as an incompatible component has a strong tendency to be enriched in the melt (i.e., with a mineral-melt partition coefficient much smaller than unity), thereby lowering the Gibbs free energy of the melt. The partitioning of water between melt and mantle minerals such as olivine, pyroxenes and garnet has been investigated extensively, but the effects of hydration on the density and transport properties of silicate melts require further assessments by experimental and computational approaches.