Low Initial Water Content Research Articles

Testing infiltration run effects on the estimated water transmission properties of a sandy-loam soil

Testing factors influencing determination of soil water transmission properties by an infiltrometer method helps better interpretation of the collected data and allows the development of appropriate sampling strategies for the intended use of the data. These factors include the soil water content at the start of the experiment, the height from which water is poured onto the soil surface, and the duration of the infiltration run. A sandy-loam soil was sampled with the BEST (Beerkan Estimation of Soil Transfer parameters) procedure of soil hydraulic characterization and two heights of pouring of water (0.03 and 1.5m) under three different initial soil water content, θi (0.12≤θi≤0.20m3m−3), conditions. According to the BEST guidelines, relatively short infiltration runs (average run duration ≤1.5h, depending on both the date and the height from which water was poured) were carried out. However, three long infiltration runs (10h) were also carried out when θi was of 0.075m3m−3. The saturated soil hydraulic conductivity, Ks, and the soil water sorptivity, S, were estimated for each infiltration run with the BEST-steady algorithm. The mean values of Ks varied with the height of pouring of water and θi from 13 to 496mmh−1, and a low height from which water was poured yielded 13 to 27 times higher Ks means than a high height, depending on θi. An inverse relationship between Ks and θi was clearer with the low height of pouring of water than the high one. The mean saturated hydraulic conductivity obtained with the long runs (15mmh−1) was close to the means of Ks obtained with the high and shorter runs (13–19mmh−1, depending on θi). The means of S varied from 35 to 126mmh−0.5, with the low runs yielding 2.3 to 2.8 times higher means than the high runs. The high sorptivity obtained with the long runs (160mmh−0.5) was in line with the low initial soil water content. In conclusion, the water application procedure and the duration of the infiltration run can have a noticeable effect on the estimated soil water transmission properties. Long duration runs or runs carried out with a high height of pouring of water appear more appropriate than short duration runs with a low height of pouring of water to obtain data usable to explain surface runoff generation phenomena during intense rainfall events, especially when the soil is relatively dry at the time of sampling. In the future, the effects of both the height from which water is poured and the run duration on the water transmission properties measured with BEST should be tested for different initial soil water conditions in other soils. The usability of the height from which water is poured onto the soil surface as a parameter to mimic high intensity rain should also be investigated specifically.

Modeling virgin compression of reconstituted clay at different initial water contents

The observations on compressibility of reconstituted clays show that the compression line with a higher initial water content lies above the compression line with a lower initial water content for a given clay. Hence there exists additional void ratio due to initial water contents among virgin compression lines (VCLs) of reconstituted clays. In this paper, the difference in void ratio caused by different initial water contents is investigated based on the empirical equation proposed by Liu and Carter (2000) for describing the differential void ratio at the same stress between natural and reconstituted clays. The mechanism of compressibility of reconstituted clays, when the stress level is larger than the remolded yield stress, is also discussed.

Laboratory investigation of the effect of cyclic wetting and drying on the behaviour of an expansive soil

The behaviour of an expansive soil was studied through a number of experiments involving cycles of wetting and drying. Laboratory tests were conducted on compacted samples of an expansive soil (a mixture of bentonite and kaolin, CH) in a modified oedometer under different constant surcharge pressures. The void ratio and water content of samples were determined at different stages. The results show that the swelling–shrinkage was reversible after the soil reached the equilibrium condition where the deformations were the same and the wetting and drying paths (in the water content–void ratio space) converged to an S-shaped curve. The hysteresis phenomenon was studied through the variation of the void ratio with suction, and the results showed that it diminished gradually with the increase in cycles of wetting and drying. The effect of fabric on the behaviour of soil samples was studied during cycles of wetting and drying. The results show that the samples with lower initial water content (on the dry side of optimum) have more swelling potential than samples with a higher initial water content (on the wet side of optimum).

Comparing the Thixotropic and Lightly Solidified Hardening Behavior of a Dredged Marine Clay

When a soil is disturbed upon remolding, it may lose part or all of its strength. As time passes, the structural arrangement of the soil particles would be restored to a stable form and the soil would regain hardness under constant volume and water content. The process is known as “thixotropic hardening”. On another note, dredged marine soils of the fine-grained type can be reused as a backfill material instead of being disposed to the open sea. The rest period required for the relocated soil to regain strength and stiffness, i.e. thixotropic hardening, needs to be estimated precisely. For this purpose, a study on the phenomena of strength and stiffness gain by a dredged marine clay was carried out. The strength and stiffness improvement with time was measured using the vane shear and fall cone tests respectively. The clay was remolded at different water contents in multiples of the soil’s liquid limit (LL), namely 0.75LL, 1.00LL and 1.25LL, in order to evaluate the effect of initial water content on thixotropic hardening. A separate series of samples were prepared with light solidification using cement, to examine the possibilities of enhancing the soil’s improvement in a shorter rest period. The results showed the dredged marine clay can potentially be used as a backfill material for reclamation works, with lower initial water content and light solidification contributing to accelerated better performance

The Thixotropic Hardening Behaviour of a Low Plasticity Dredged Marine Silt

An alternative to solve the problem of disposing dredged marine sediments (DMS) in open sea, which could lead to undesirable contamination and destruction of the marine ecosystem, is to reuse the material in reclamation works. For such applications, it is important to determine the time required for strength gain of the relocated DMS. A lab-based study was conducted to simulate and examine the post-consolidation hardening of DMS when placed as a backfill with relation to time. A separate series of tests were also carried out on the DMS being lightly solidified with cement, with the purpose of identifying potential shortening of the waiting period. The DMS sample was prepared at different water contents based on the soil's liquid limit (LL = 54.5 %), i.e. 0.90, 1.25 and 1.81LL. The undrained shear strength was measured using the laboratory vane shear (VS) test. Complementary fall cone (FC) tests were conducted for additional information on the improved remoulded strength and stiffness of the DMS. The results showed that the strength and stiffness (cone penetration resistance) of the relocated DMS could effectively improve with time, though the rest period required is shorter for a sample with lower initial water content. On the other and, light cementation shortened the rest period, and significantly improved the strength and stiffness at dosages as low as 5 % (as per dry weight of the soil). Overall the study gave an overview of the reusability of DMS as a backfill material in reclamation works, whether with or without lightly induced solidification, depending mainly on the limitations of rest period available.

Managing crop stubble during fallow period for soil water conservation: field experiment and modelling

In the arid and semi-arid environments where the rainfall is limited and variable, fallow period soil moisture conservation using stubble is one of the ways of increasing the soil moisture required for crop sowing and development. However, the effectiveness of moisture conservation using stubble depends on the paddock management, soil water content, and rainfall characteristics. To assess the effect of stubble rate and amount of rainfall on the soil moisture conservation, a two-season field experiment was conducted using four stubble rates (0, 2, 4, 6 t/ha) and two water supply amounts. The soil water dynamics was also analysed using a validated Agricultural Production System Simulator (APSIM). In the relatively wet summer season with a high initial soil water content, the amount of water stored in the 2, 4, and 6 t/ha stubble rate treatment plots was higher than that of the bare plots by 10.4, 15.9, and 17.8 mm, respectively. However, in the summer season with a relatively high amount of in-season water input and low initial soil water content, the soil water storage was increased by 29.4, 35.6, and 43.0 mm, respectively. Comparing the results of the two seasons, the highest increase was observed for the 2 t/ha stubble rate. The amount of conserved soil moisture was found to be the highest when the soil profile water content at the start of the summer-fallow period is low and the amount of rain during the summer season is high. The good agreement between the measured and APSIM-simulated soil water contents (R 2 = 0.812), indicates that the model can be used to assess the soil water dynamics under a fallow condition. The APSIM-simulated soil water balance using the weather data of the past 100 years indicated that in a year with low start-of-fallow period soil water content, a 6 t/ha stubble rate can increase the end-of-fallow period soil moisture by up to 60 %.

Thermogravimetric and calorimetric study of cellulose paper at low doses of gamma irradiation

The study of the behaviour of cellulose materials at low doses of ionizing radiation regained the interest because of the recent results showing that physical properties of the paper have less or no changes for absorbed doses below 10 kGy, despite the high decrease of the degree of polymerization. The understanding of the relationship among molecular, microscopic and macroscopic changes in cellulose materials may change the current opinion that irradiation of paper is not the best choice for conservation of cultural heritage. The aim of this study is to reveal the changes in gamma-irradiated pure cellulose paper by simultaneous TG/DSC analysis. For cellulose fibres, the thermal decomposition parameters depend on the cellulose degree of polymerization. For high irradiation doses, there is established a relationship between the absorbed dose and the degree of polymerization. However, a direct relationship between absorbed dose and the parameters of cellulose thermal decomposition for low irradiation doses was not established either in the literature or in our study. By using a peak separation technique, we studied the changes in the region of water loss (70–150 °C) and physical ageing (160–300 °C) for Whatman paper with low initial water content (<1 %), previously gamma irradiated at doses between 0 and 30 kGy. We concluded that strength of the hydrogen bond structure is increasing up to a point when the stress produces fractures in the fibrilar structure. This may explain the results reported for mechanical tests at low dose irradiation and it is in agreement with scanning electron microscopy pictures showing changes in fibril structure at high irradiation doses. Cellulose irradiated at low doses maintains its original hydrogen bond structure despite the decrease of the degree of polymerization.

Continuous production of biodiesel using whole-cell biocatalysts: Sequential conversion of an aqueous oil emulsion into anhydrous product

A continuous production of biodiesel from an aqueous plant oil emulsion was attempted using immobilized fungal whole cells. Six packed-bed reactors were connected in series and operated with stepwise methanol addition. In the first column, more than 3% water was necessary for methanolysis to proceed. Despite the low initial water content of 0.36%, the methyl ester content in the effluent from the second column increased similarly in a wide range of contents of water (0–20%) added, which shows the water-content-independent reaction in this column in contrast to the reaction in the first column. Further investigations using reaction mixture models suggested a contribution of the composition of the reaction mixture to the phenomenon. On the basis of these findings, the sequential methanolysis through six columns was attempted, where the upper layer of the effluent from each column was supplied into the next column without further addition of water. Consequently, an aqueous plant oil emulsion with 3% water was converted into the final product with 96.1% methyl ester and 0.15% water. Therefore, the system developed is useful for producing biodiesel enzymatically from water-containing feedstocks.

Leachate formation and characteristics from gasification and grate incineration bottom ash under landfill conditions

Characteristics and formation of leachates from waste gasification and grate firing bottom ash were studied using continuous field measurements from 112m3 lysimeters embedded into landfill body for three years. In addition, the total element concentrations of the fresh ash were analysed and laboratory batch tests were performed to study leachate composition. The three-year continuous flow measurement showed that about one fifth of the leachates were formed, when the flow rate was >200l/d, covering <3.5% of the study time. After three years, the liquid/solid-ratio for the quenched grate ash was 1 (l/kg (d.m.)) and for the initially dry gasification ash 0.4 (l/kg (d.m.)). The low initial water and residual carbon content of the gasification ash kept the leachate pH at a high level (>13) major part of the study. In the grate ash leachate pH was lower (<8) due to the presence of organic carbon and biodegradation indicated by biological oxygen demand and redox potential measurements. In the gasification ash the high pH probably delayed leaching of major elements such as Ca, therefore, raising the need for a longer after-care period. The high pH also explains the higher leaching of As from the gasification ash compared to the grate ash both in the batch test and under landfill conditions.

Electrochemical Impedance Spectroscopy Detection of Saturation Level in a Frozen Polymer Electrolyte Membrane Fuel Cell

A modified electrochemical impedance spectroscopy (EIS) method has been developed to probe fundamental hydration properties in polymer electrolyte membrane fuel cells (PEMFCs) related to subzero cold-start phenomena. Subzero cold-starts are vital to widespread automotive PEMFC commercialization. The EIS method is specifically sensitive to the charge transfer and diffusional resistances of the membrane electrode assembly (MEA). The lower initial water content [ vs 3.2 (mol )] of the PEMFC negatively impacted the initial ohmic and charge transfer resistances. Isothermal water fill tests (WFTs) were performed at to make discrete increases in water content within the MEA. The initial water content affected water uptake of the ionomer ( vs 3.2 was almost double) and the change in ohmic and charge transfer resistances. EIS performed at three stages—pre-WFT, hydrated, and freeze-out—show specific changes. In initial WFTs, the ohmic resistances decrease to similar values ( for , for ). Diffusional changes are negligible. In freeze-out WFTs, ice forms in the catalyst layer. An increase in the ohmic resistance and almost tripling of the diffusional resistance were observed for and 3.2. Ice produced in the void volume and changes in the diffusional resistance were not significantly affected by the preconditioned initial water content ( vs 3.2).

Effect of Cathode Pore Volume on PEM Fuel Cell Cold Start

Start-up of a proton exchange membrane (PEM) fuel cell from subzero temperatures, commonly referred to as cold start, remains a major challenge for automotive applications. In this work, we theoretically and experimentally study the effect of catalyst layer (CL) pore volume (or, more directly, CL thickness) on the cold-start performance of a PEM fuel cell for both isothermal and nonisothermal operations. Special attention is directed to determining the limits of a cold-start performance with an ultrathin CL . The cold-start product water or the operational time approaches a minimum nonzero asymptote as the CL is gradually made infinitesimally thin. For a PEM fuel cell with standard cell thermal mass, e.g., , and with moderately low initial membrane water content , successful start-up from at can be achieved for CL thicknesses of and above, whereas a CL thickness of is required for successful self-start-up from . However, successful start-up can be achieved even with a thick CL, given certain adjustments to cell design and material properties. In particular, we study the effects of cell thermal mass and membrane water diffusivity and present a design map for self-start-up of a CL PEM fuel cell from various subfreezing temperatures.

Relative Humidity Controls Ammonia Loss from Urea Applied to Loblolly Pine

In the United States, approximately 600,000 ha of pine trees are fertilized with urea each year, with NH3 volatilization losses ranging from &lt;1% to &gt;50% depending on environmental conditions. Previous work showed that the timing of rainfall after urea application plays a significant role in controlling NH3 loss, but the effect of other environmental variables is not well understood. We conducted 10 29‐d studies under different environmental conditions during 2 yr to identify important variables controlling NH3 loss from urea applied to loblolly pine (Pinus taeda L.) at 200 kg N ha−1 Ammonia loss was measured with dynamic chambers that adjusted the rate of air flow through the system based on wind speed at 1 cm above the soil surface. Regression analysis indicated that a variable related to the initial water content of the forest floor and a variable related to the relative humidity (RH) during the study explained 85 to 94% of the observed variability in NH3 loss. Relatively high initial water content followed by consistently high RH led to large NH3 losses. In contrast, low initial water contents resulted in slow rates of NH3 loss, which increased when elevated RH led to an increase in the water content of the forest floor. These results indicate that RH can play a significant role in NH3 loss by accelerating urea dissolution and by increasing or decreasing the water content of the forest floor, which in turn can affect the rate of urea hydrolysis.

Late Shield-Stage Silicic Magmatism at Wai'anae Volcano: Evidence for Hydrous Crustal Melting in Hawaiian Volcanoes

Late shield-stage silicic (icelandite and rhyodacite) lavas and dikes are exposed within the caldera region of Wai‘anae Volcano, O’ahu, and comprise the most continuous silicic, subalkaline and transitional suites in Hawai‘i. The silicic rocks can be divided into two groups. Group I consists of transitional icelandite dikes and icelandite to basaltic icelandite lava flows that follow a tholeiitic liquid line of descent. Group II includes the Mauna Kūwale Rhyodacite and several intermediate-silica lavas that follow a K-rich, calc-alkaline evolutionary trend. Group II lavas are highly porphyritic, with biotite and hornblende in the rhyodacites, and are selectively enriched in Rb, U and Pb. Pb, Sr and Nd isotope ratios of a Group I dike are similar to those of other Wai‘anae basaltic samples, whereas Group II lavas have lower 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and e Nd , and high ratios of radiogenic 208 Pb*/ 206 Pb*, similar to some lavas from Ko’olau, Lāna‘i, and Kaho’olawe volcanoes. Most Group I dikes define a trend consistent with fractional crystallization at ∼0·5 kbar with low initial water (0·3 wt %) contents, whereas the chemical trends for Group II samples cannot be reproduced by simple crystallization models. These results, together with trace element modeling and isotopic characteristics, suggest derivation of the Group II silicic flows by hydrous melting of lower Hawaiian crust that had been altered to amphibolite. Crustal melting toward the end of the shield stage may be related to an increase in lithostatic pressure following rapid accumulation of lavas in the shield stage and ponding of basaltic magmas at depths below the level of crack closure (∼9–10 km). Contemporaneously, Group I silicic magmas formed by shallow-level crystallization as a consequence of decreased magma supply to the upper crust as a result of waning activity at the end of the shield stage. Geochemical evidence indicates significant mixing between the different types of silicic magma and between basaltic and silicic magmas at this stage of volcano evolution. Although melting of recycled crustal material entrained in the upwelling Hawaiian plume has previously been proposed, this is the first documentation of a role for melting of lower Hawaiian crust in the genesis of Hawaiian volcanoes.

Leaf water absorption and desorption functions for three turfgrasses

Summary Plant leaf can absorb water when the leaf is in contact with water. This happens when the rainfall is intercepted by plant leaves, where the intercepted part of rain remains on the leaf surface. When the intercepted water is either absorbed or subsequently evaporated into the atmosphere, the plant leaves can dissipate water through the desorption process until the plant is dry or rewatered. In this paper, two symptomatic models in the form of exponential functions for leaf water absorption and leaf water desorption were derived and validated by experimental data using leaves of three turfgrasses (Tall fescue, Perennial ryegrass and Kentucky bluegrass). Both the models and measured data showed that the rate of leaf water absorption was high at the low initial leaf water content and then gradually leveled off toward the saturated leaf water content. The rate of leaf water desorption was high at the high initial leaf water content then decreased drastically over time toward zero. The different plant leaves showed different exponents and other parameters of the functions which indicate the difference of plant species. Both the absorption and desorption rates were relatively higher for the Kentucky bluegrass and lower for the Tall fescue and Perennial ryegrass. The concept of specific leaf area (SLA) was used to understand the saturated leaf water content (Cs) of the three turfgrasses. Linear relationships were found between Cs and SLA. The leaf water absorption and desorption functions are useful for deriving physiological parameters of the plant such as permanent wilting leaf water content, naturally irreducible leaf water content, exponential leaf water absorption coefficient, and exponential leaf desorption coefficient, as well as for evaluating the effects of rainfall interception on plant growth and water use efficiency.

Numerical studies of cold-start phenomenon in PEM fuel cells

In this paper, a PEM fuel cell model for cold-start simulations has been employed for numerical investigations of the cell startup characteristics from subfreezing temperatures. The effects of many key parameters on fuel cell isothermal cold-start behaviors have been carefully examined. Numerical results indicate that a high gas flow rate in the cathode gas channel, a low initial membrane water content, a low current density under the constant current condition, and a high cell voltage under the constant cell voltage operation are beneficial for the PEM fuel cell isothermal cold-start processes. Increasing the startup cell temperature would significantly delay ice formation and consequently lead to longer cold-start time. Therefore, incorporating internal and external heating sources in the cell design scheme is very important for achieving fast and successful cold start of a PEM fuel cell from subfreezing temperatures.

Stabilizing Formulations for Inhalable Powders of Live-Attenuated Measles Virus Vaccine

Carbon dioxide Assisted Nebulization with a Bubble Dryer((R)) (CAN-BD) processing allows particles to be made in the 3-5 mum size range, which is desirable for lung delivery, without destroying biological activity. In response to the Grand Challenge in Global Health Initiative #3, we have been developing an inhalable needle-free live-attenuated measles virus vaccine for use in developing countries. Measles was chosen because it is the number one vaccine preventable killer of children worldwide. Powders were processed by CAN-BD, where a solution containing excipients and live-attenuated measles virus in water was mixed intimately with supercritical or near superctitical carbon dioxide to form an emulsion. The emulsion was expanded to atmospheric pressure through a flow restrictor. The resulting plume was dried by heated nitrogen and the powders collected on a filter at the bottom of the drying chamber. Powders were analyzed using varying techniques including X-ray diffraction, scanning electron microscopy, Andersen cascade impaction, differential scanning calorimetery, Karl Fischer titration, and viral plaque assay. CAN-BD has been used to produce powders of live-attenuated measles virus vaccine with characteristics desirable for lung delivery. The powders retain viral activity through forming and drying the microparticles by CAN-BD, and have passed the WHO stability test for 1 week at 37 degrees C. The powders have an amorphous character and a glass transition temperature of around 60 degrees C. Lyophilization, the present standard commercial method of processing measles vaccine makes solids with a water content of less than 1%. By substituting myo-inositol for sorbitol and using the CAN-BD drying technique the water content can be lowered to 0.5%. The most successful formulations to date have been based conceptually on the current lyophilized formulation, but with modifications to the type and amounts of sugar. Of current interest are formulations containing myo-inositol, as they retain high viral activity and have low initial water content.

Quantifying risk for water harvesting under semi-arid conditions: Part II. Crop yield simulation

Risk assessment of maize yield was carried out using a crop growth model combined with a deterministic runoff model and a stochastic rainfall intensity model. These were compared with empirical models of daily rainfall–runoff processes. The combination of the deterministic runoff model and the stochastic rainfall intensity model gave more flexible performance than the empirical runoff model. Scenarios of crop simulation included production techniques (water harvesting, WH, and conventional total soil tillage, CT) and initial soil water content at planting (empty, half and full). The in-field water harvesting technique used in the simulation was a no-till type of mini-catchment with basin tillage and mulching. The lower the initial soil water content at planting, the greater the yield difference between the WH and CT production techniques. With the low initial soil water content at planting, the WH production technique had up to 50% higher yield compared to the CT production technique, clearly thus demonstrating the superiority of the WH production technique. Under all the variations in agronomic practices (planting date, plant population, cultivar type) tested, the WH had a lower risk than CT under these semi-arid climatic conditions (i.e., WH increased the probability of higher crop yields).

Retention performance of geotextile containers confining geomaterials

The design of geotextile containers for dewatering applications typically requires hydraulic compatibility between the geotextile and the confined fill material. Ideally, a geotextile container must successfully retain the solid phase of the fill material and must not be clogged during the dewatering process. This becomes difficult to achieve when the fill material is fine grained and the pore openings are large, such as with traditional geotextile containers. Fly ash and bottom-sea dredged sediments are some of the fine-grained geomaterials that exhibit behaviour that is different from that of regular soils because of differences in their particle structure and chemical composition. In most cases, existing geotextile filter selection criteria are not directly applicable to these unusual geomaterials: therefore an evaluation of the filtration performance of such materials is necessary. A laboratory testing programme was conducted to evaluate the retention performance of geotextiles with fly ash and bottom-sea dredged sediments. The results indicated that both fly ash and dredged sediments could be successfully retained by a variety of woven geotextiles and nonwoven/woven combinations. Results also showed that use of a double-layer geotextile system, rather than a single woven geotextile, significantly increased the retention capacity. Geotextile hydraulic properties such as permittivity and the apparent opening size had little effect on dewatering efficiency; however, the same properties directly influence the retention performance. Additionally, a relatively low initial water content of slurry and the filter cake formed at the soil/geotextile interface promote the retention performance. Geotextile apparent opening size-to-soil particle size ratios in the existing retention criteria did not always accurately predict the observed performance. Therefore a parametric study is needed to evaluate various ratios and to find the most discriminating ratio for retention performance.

Retention performance of geotextile containers confining geomaterials

The design of geotextile containers for dewatering applications typically requires hydraulic compatibility between the geotextile and the confined fill material. Ideally, a geotextile container must successfully retain the solid phase of the fill material and must not be clogged during the dewatering process. This becomes difficult to achieve when the fill material is fine grained and the pore openings are large, such as with traditional geotextile containers. Fly ash and bottom-sea dredged sediments are some of the fine-grained geomaterials that exhibit behaviour that is different from that of regular soils because of differences in their particle structure and chemical composition. In most cases, existing geotextile filter selection criteria are not directly applicable to these unusual geomaterials: therefore an evaluation of the filtration performance of such materials is necessary. A laboratory testing programme was conducted to evaluate the retention performance of geotextiles with fly ash and bottom-sea dredged sediments. The results indicated that both fly ash and dredged sediments could be successfully retained by a variety of woven geotextiles and nonwoven/woven combinations. Results also showed that use of a double-layer geotextile system, rather than a single woven geotextile, significantly increased the retention capacity. Geotextile hydraulic properties such as permittivity and the apparent opening size had little effect on dewatering efficiency; however, the same properties directly influence the retention performance. Additionally, a relatively low initial water content of slurry and the filter cake formed at the soil/geotextile interface promote the retention performance. Geotextile apparent opening size-to-soil particle size ratios in the existing retention criteria did not always accurately predict the observed performance. Therefore a parametric study is needed to evaluate various ratios and to find the most discriminating ratio for retention performance.

An experimental study on the shallow-level migmatization of ferrogabbros from the Fuerteventura Basal Complex, Canary Islands

Spectacular shallow-level migmatization of ferrogabbroic rocks occurs in a metamorphic contact aureole of a gabbroic pluton of the Tierra Mala massif (TM) on Fuerteventura (Canary Islands). In order to improve our knowledge of the low pressure melting behavior of gabbroic rocks and to constrain the conditions of migmatization of the TM gabbros, we performed partial melting experiments on a natural ferrogabbro, which is assumed as protolith of the migmatites. The experiments were performed in an internally heated pressure vessel (IHPV) at 200 MPa, 930–1150 °C at relatively oxidizing conditions. Distinct amounts of water were added to the charge. From 930 to 1000 °C, the observed experimental phases are plagioclase (An 60–70), clinopyroxene, amphibole (titanian magnesiohastingsites), two Fe–Ti oxides, and a basaltic, K-poor melt. Above 1000 °C, amphibole is no longer stable. The first melts are very rich in normative plagioclase (>70 wt.%). This indicates that at the beginning of partial melting plagioclase is the major phase which is consumed to produce melt. In the experiments, plagioclase is stable up to high temperatures (1060 °C) showing increasing An content with temperature. This is not compatible with the natural migmatites, in which An-rich plagioclase is absent in the melanosomes, while amphibole is stable. Our results show that the partial melting of the natural rocks cannot be regarded as an “in-situ” process that occurred in a closed system. Considerable amounts of alkalis probably transported by water-rich fluids, derived from the mafic pluton underplating the TM gabbro, were necessary to drive the melting reaction out of the stability range of plagioclase. A partial melting experiment with a migmatite gabbro showing typical “in-situ” textures as starting material supports this assumption. Crystallization experiments performed at 1000 °C on a glass of the fused ferrogabbro with different water contents added to the charge show that generally high water activities could be achieved (crystallization of amphibole), independently of the bulk water content, even in a system with very low initial bulk water content (0.3 wt.%). Increasing water contents produce plagioclase richer in An, reduces the modal proportion of plagioclase in the crystallizing assemblage and extends the melt fraction. High melt fractions of >30 wt.% could only be observed in systems with high bulk water contents (>∼2 wt.%). This indicates that the migmatites were generated under water-rich conditions (probably water-saturated), since those migmatites, which are characterized as “in-situ” formations, show generally high amounts of leucosomes (>30 wt.%).