V31C-0596
Pyrite Recrystallization Experiments With Circulating Hydrothermal Solution
Pyrite is one of the most common sulfide minerals found in hydrothermal deposits and sea-floor sediments from hydrothermal fumaroles. Hydrothermal fluid flow plays an important role in crystallization of sulfide minerals. In this study, we tried to reproduce pyrite crystallization with one-way flowing hydrothermal fluid. We designed a circuit circulating hydrothermal fluid by thermal convection. A rectangular circuit (42.6 cm by 17.3 cm) of SUS316 pressure tubes with 5 mm in inner diameter was used as a reaction vessel. In the circuit, pyrite dissolves to acidic fluid in upstream region. Then, pyrite will crystallize again in downstream region as temperature decreases. The rectangular plane was held to be 20 degrees inclination to generate thermal convection. One of the long sides of the rectangular was heated by an electric furnace. Starting materials were put in a tube to be heated. Upper half, approximately 20 cm, of the tube was filled with quartz sand. Next quarter was filled with equivalent mass mixture of quartz sand and powdered pyrite crystals. The lowest quarter was filled with mixture of quartz sand, pyrite, anhydrite and sulfur, those mass are equivalent. The solution was a mixture of 0.5mol/l HCl and 3.0mol/l NaCl. Maximum temperature was controlled to approximately 350°C at the center of the heated tube. Experimental durations were up to 9 days. Fluid pressure increased to approximately 6 MPa as heating. After the experiments, the run products were fixed with resin in a sample tube, and vertical sections were observed by SEM. In the run products, pyrite dissolved at the lower part of the starting material. In the upper half of the sample tube, pyrite crystals precipitated on quartz surface. Crystallization density depends on temperature gradient of the fluid. Predominant morphology of the pyrite crystals consists (100) plains. Tiny framboidal aggregates and crystals with (210) plains also occur. In the run products of longer than 3 days run durations, platy elongated crystals with (100) plains occur. Platy crystals are almost parallel to the surface of the host quartz grains. High temperature fluid flow and condensation of vapor phase may control nucleation density, crystal morphology and growth habit of pyrite crystals in hydrothermal fluid.
V31C-0597
Partial Molar Volumes of Components and Species in O-S-Fe-Ni Oxide and Sulfide Liquids
High-quality thermochemical models are now available for sulfide liquids at one bar pressure. An accurate description of the volume mixing properties of these liquids is required in order to apply these one-bar models to important problems at elevated pressure, including sulfide-hosted ore formation, sulfur cycling in convergent margin settings and core formation. Our experimental data have been combined with select density data from other laboratories to calibrate a comprehensive model for density and partial molar volumes of liquids in the O-S- Fe-Ni system. Our results indicate significant negative deviation from linear mixing across the Fe-S, Ni-S and Cu-S binaries. This result is in qualitative agreement with those from prior studies. In the context of associated homogeneous speciation models for sulfide liquids (Kress, 2000, 2007), this negative volume of mixing can be interpreted as a strongly negative volume of reaction for the formation for intermediate melt species from end member elemental components (Δ Vf). Our regression yields Δ Vf values of -6.2, -9.4 and -9.1 cc/mol for FeS, NiS and CuS respectively. There is insufficient oxygen in experimental liquids to resolve a composition dependence for v̄O, but the unrealistic negative regressed value for oxygen partial molar volume suggests a negative Δ Vf for FeO and FeO1.5. Partial molar volumes of Fe, Ni and Cu liquid species are calculated from Nash and Steinemann (1995). All other v̄i are assumed to be linear mixtures of component species volumes. This assumption also implies a moderate negative Δ Vf for the species in question. The resulting model reproduces experimental densities from our laboratory with a 3.6% average error. This is comparable to the estimated measurement error. The larger 5.1% error for the full data set can be attributed to lower precision in some of the other studies and the effects of inter-laboratory error. The sulfide volume model can be applied to calculate thermochemical properties of sulfide liquids to moderate pressures. This model is used in conjunction with literature experiments on coexisting sulfide and silicate liquids at pressure to explore complex interactions between the pressure dependences of oxygen fugacity, sulfur fugacity and sulfide saturation.
V31C-0598
Carbonate Solid Solution Models to 6 GPa
At convergent boundaries, volatile compounds are transported in the interior of the Earth affecting the chemical evolution of our planet. H2O and CO2 are the most important compounds affecting phase stabilities during subduction. The stability of carbonates at high pressure is proved by the occurrence of coesite and diamond inclusions in dolomite and magnesite from carbonate-bearing eclogite, with the general succession of carbonates with pressure being calcite - dolomite - magnesite. The fate of carbonates, is controlling the residence time of C in the mantle, affecting its global geochemical cycle and contributing to the chemical and, in carbonate rich sediments, also mechanical structure of subducted crust. Nevertheless the phase diagram of CaCO3- MgCO3- FeCO3 is unknown at high pressure and is now investigated to 6 GPa and 1300 °C. Starting materials are natural MgCO3, synthetic CaCO3 and FeCO3 in different proportions. Preliminary experiments have been carried out at 3.5 GPa, 900 °C in Pt-C capsules to fix oxygen fugacity roughly to GCO, thus avoiding siderite oxidation. These runs show a broad miscibility field between CaCO3 and CaMgxFe1-x(CO3)2, which is in agreement with the observation of (Mg,Fe)- calcites with high Mg+Fe contents in experiments on natural bulk compositions. At this P-T conditions ankerite is not been observed, it has been observed a continuous solid solution between dolomite and CaMg0.2Fe0.8(CO3)2 . Between CaMgxFe1-x(CO3)2 and the continuous solid solution siderite-magnesite exist a broad miscibility gap; no three phase field has been noted. Selected runs have been observed with TEM to investigate disordering and reordering after quench, future synchrotron X-ray diffraction will determine in-situ the state of disorder of carbonates and the transition, and quantify the experimental "quenchability" of disordering. Further experiments at different P-T conditions in piston cylinder and multi anvil apparatus are necessary to obtain a full set of thermodynamic properties and a full fledged solid solution model as a function of pressure and temperature.
V31C-0599
The Importance of Chemical Compostion on the Electrical Conductivity of Silicate Melts
The electrical conductivity of geomaterials can vary by several orders of magnitude over small changes in temperature and/or chemical composition. The variation in electrical conductivity of Earth's mantle is largely dependent on temperature as it increases from approximately 0.01 S/m in the upper mantle to 1 S/m in the shallow depths of the warmer lower mantle. Activation energies for electrical conduction of iron-bearing silicate minerals are on the order of 1 eV and depend mostly on Fe and H2O contents. Over a more restricted temperature range, the importance of chemical composition on the conductivity of natural silicate melts is much more evident. From a database of several experimental data we have generated an empirical model for the electrical conductivity of natural silicate melts as a function of chemical composition and temperature. The data include those obtained in our laboratory and others taken from the literature. All melts are anhydrous and we take into account seven major chemical components (SiO2, Al2O3, Na2O, K2O, MgO, CaO, and Fetot) in addition to temperature. Various forms of equations are utilized (Arrhenian-based, VTF-based) with the aim of minimizing both standard error and number of adjustable parameters. In some cases, the resulting fit parameters show strong correlations to other properties (e.g. cation field strength) of their respective chemical components. We also address partially molten systems and how both melt composition and volume fraction affect bulk conductivity. Interestingly, in a basaltic system melt fraction appears to be more important than melt composition in affecting bulk conductivity. However, in more alkali-rich systems, melt composition plays a much more important role and the variation of electrical conductivity with increased melting can be complex. These results can be potentially useful for locating and estimating the size of magmatic reservoirs in regions where magnetotelluric data are available.
V31C-0600
The Rheological Behaviour of Vesuvius Magmas
Somma-Vesuvius is considered one of the highest-risk volcanoes of the world due to its high population density and the large variability of its past explosive activity. Eruptive style at Vesuvius largely varies from effusive to explosive and is strongly controlled by the evolution of the physical and chemical properties of the magma. However, with the exception of previous investigations of the 1631 eruption [1,2], rheological properties of Vesuvius products are still unconstrained. Here, we investigate the viscosity of dry and hydrous remelted glasses from the Mercato (plinian) and 1906 (violent strombolian) eruptions that differ for size, eruption styles and chemistry (phonolite vs. phonolitic tephrite). In addition, we also investigate the rheological properties of the total rocks and matrices of the products of the Pollena and the Pompei eruptions. Preliminary results on the rheology of the liquid+crystals mixtures were obtained at high-T using concentric cylinder. Low T viscosities were measured using micropenetration viscometry. The results from this study were parameterized by a modified Vogel-Fulcher-Tammann equation, accounting for the effect of water and composition, and compared with previous measurements [1,2]. The results show that the high T viscosities differ by as much as 2.5 orders of magnitude and that it varies from close to Arrhenian to significantly non- Arrhenian depending on composition. Hydrothermal syntheses were performed for the Mercato and the 1906 eruption. The results show that the viscosity strongly decreases with water content, the decrease being more marked at low water contents. Isothermal holds measurements on Vesuvian melts suggest that non-Newtonian rheology occurs even at low crystal contents. Isothermal holds viscosity measurements can also define a time-temperature-viscosity window over which crystallization occurs. Results indicate that below 1150°C a very rapid viscosity increase occurs due to a high crystallization rate. [1] Romano et al., 2003, Chem. Geol. 202, 23-38; [2] Giordano et al., 2006, Chem Geol. 229,42-56
V31C-0601
Fluid-mineral interactions in subduction zones: insights from experiments in the diamond- anvil cell
Volatile-rich high-pressure fluids released into the mantle during the subduction of the oceanic lithosphere have a broad impact on the mass transfer in the Earth since they mediate the recycling of elements into the mantle and their return to the atmosphere through arc volcanism. Constrains on element transport and mass fluxes in these environments rely on quantitative thermodynamical modeling of fluid-mineral interactions, that is greatly limited by the lack of thermodynamic data of aqueous fluids at high pressure and temperature conditions (10 GPa – 800 C). As a part of the efforts to adress this problem, this contribution will present recent results on it in situ studies of fluid-mineral interactions at high P-T conditions in the diamond anvil cells using synchrotron X-ray and vibrational spectroscopies. Experiments designed to measure in situ the solubility of mineral, the distribution of stable isotopes between minerals-melts-fluids and the density of aqueous fluids will be presented. Synchrotron X-ray Fluorescence spectroscopy (SXRF) has been used to conduct it in situ dissolution/precipitation kinetics studies and mineral solubility measurements with detection limits as low as 40 ppm in the diamond-anvil cell. Results on the solubility of carbonate minerals in water will be shown to illustrate the potentials of the technique for in situ observations of mineral-fluids interactions at extreme conditions. In another example we report investigations on the systematic of boron isotopic fractionation between mineral/melt/fluid at subduction zone conditions. Boron isotopic fractionation factors between trigonal B(OH)3 and tetragonal B(OH)4- aqueous species at high P-T conditions (10 GPa – 500 C) were calculated using measured vibrational spectra (Raman and IR) and thermodynamical modeling following Urey's theory. Combining these results with previous data on B-isotopic fractionation between minerals/melts/fluids we propose a model in which B-isotopic exchanges at high P-T conditions can be quantitatively predicted from coordination changes between phases, be it solids or fluids. Finally, efforts on the evaluation of the thermodynamic properties of high pressure fluids will be illustrated by the determination of the equations of state from sound velocity measurements in the diamond-anvil cell by Brillouin scattering spectroscopy. Densities of H2O and NaCl-H2O fluids will be presented and discussed in comparison with literature data.
V31C-0602
Experimental Studies on Rutile Solubility
Rutile (TiO2) is an important high field strength element (HFSE) sequestering mineral, and has been implicated in the observed depletion of HFSE in arc magmas. It is thought that rutile is insoluble in slab-derived fluids, and remains residual in the subducted slab. Indeed, experimental data indicates a very low solubility of rutile in pure H2O (Tropper and Manning, 2005), and this low solubility may result in HFSE depleted fluids imparting a depleted signature to arc magmas. However, there is scant experimental data available on rutile solubility in fluids of more complex compositions (Ayers and Watson, 1993). We are carrying out a systematic experimental study into the effect of specific chemical components on rutile solubility in fluids and also silicate melts. This should further our understanding of HFSE mobility in metamorphic rocks within subduction zones. References: J. C. Ayers and E. B. Watson (1993) Rutile solubility in supercritical aqueous fluids and the high P-T mobility of elements it concentrates. Contrib. Mineral. Petrol. 114, 321-330. P. Tropper and C. E. Manning (2005) Very low solubility of rutile in H2O at high pressure and temperature, and its implications for Ti mobility in subduction zones. American Mineralogist 90(2-3), 502-505.
V31C-0603
Bridging the piston-cylinder/multi-anvil gap
The piston-cylinder device is a favored tool for studying rocks under Earth's crust and uppermost mantle conditions. Experiments on fairly large sample volumes featuring careful control of pressure, temperature, oxygen fugacity, volatile content etc. are routine in this device, up to 3.0 GPa (non end-loaded) and 5.0 to 6.0 GPa (end-loaded). For higher-pressure studies, the multi-anvil takes the place of the piston-cylinder as the primary large-volume device. However, there is a notable gap in several capabilities when transitioning from the piston-cylinder to the multi-anvil. Because the furnace is necessarily shorter in a multi-anvil, thermal gradients are higher and the available volume is smaller. This makes it more difficult to control many environmental variables, such as oxygen fugacity, in a multi-anvil experiment. Much higher friction in the system means that pressure accuracy is lower. Also, it is more difficult to use quasi-hydrostatic media such as NaCl, which means that stresses and pressure gradients are likely to be higher. Current developments are aimed towards partially bridging this capability "gap" between piston-cylinders and multi-anvils. The development of new large-volume assemblies, through the COMPRES cell development project, will be described, in particular new larger octahedral assemblies with 18 and 25 mm edge lengths. A fundamental redesign of the furnace from the elongated furnaces characteristic of the piston-cylinder, which gain their low thermal gradients sinply from the length of the furnace (an infinite tubular furnace would have no thermal gradient inside) is necessary. While some laboratories have chosen step-heaters to reduce thermal gradients, we are experimenting with box heaters that are surrounded by a thermal insulating material (zirconia) and have very small electrical leads to avoid heat loss. The large sample volumes resulting from this design allow low- gradient experiments with sample volumes the same as those of a 3/4" piston-cylinder assembly up to 5 or 6 GPa (25/15 assembly) and a 1/2" piston-cylinder up to 8 or 10 GPa (18/12 assembly). This allows better control of external variables than is possible in smaller-volume or higher-gradient assemblies. Some problems, such as the higher friction and higher pressure uncertainty, are not solved, but we can combine the fact that the multi- anvil has been modified for in-situ x-ray experiments, allowing pressures to be measured directly, with more careful control of assembly components, to at least partially overcome this accuracy problem. These and other developments are being used to create a smoother transition from piston-cylinder to multi-anvil experimental conditions.
V31C-0604
Experimental Characterization of Redox Changes During Degassing of a Vapor Saturated Magma: Redox Exchanges Between H-O-Fe Species
The redox state of a magma reaching the surface is generally thought to be buffered by its iron redox ratio during ascent, reflecting therefore that of its source region. Only recently, the role of volatiles degassing on redox state of silicic magmas has been quantitatively addressed using numerical modelling. In these iron-poor magmatic systems, oxygen fugacity (fO2) is almost dominated by the chemical potential of the H2 and H2O volatile components. Because water is several orders of magnitude more soluble than molecular hydrogen in molten silicate, it was found that the ratio of their chemical potential dramatically changes during closed system degassing leading to an increase in fO2 of 2 orders of magnitude. We present here the results of an experimental test of such an oxidation event associated to the decompression of silicic melts saturated in volatiles. A peralkaline synthetic composition containing 2-4wt percent of dissolved iron oxides is used as starting material. Experiments are performed in cold seal pressure vessels pressurized with pre-mixed argon and hydrogen bottles. All experiments are equilibrated under water-saturated conditions at 800°C and variable pressures between 200 MPa and 25 MPa. Experiments were ended by rapid drop quench. Three oxygen fugacity conditions were investigated by using pure Argon (NNO+3) and two Ar-H2 mixtures buffering fO2 conditions at NNO+1.5 and NNO. Water content was determined using infrared spectroscopy and Karl-Fisher titration and the iron redox ratio was measured by wet chemistry. All run products are free of crystals. Time series experiments at fixed pressure were performed to determine the equilibrium dependence of iron redox ratios on pressure. Decompression experiments were performed from an equilibrated vapor-saturated melt at 200 MPa, lasted from few minutes to few hours, and were quenched at 100 MPa to 25 MPa. The measured iron redox ratios after decompression do not considerably differ from the ones before decompression. A slight oxidation is however noticed for some experiments, which can correspond to 0.7 log- units of fO2 increase in the most favorable cases. We conclude that a "Le Chatelier effect" most likely dominates and restricts the fO2 increase that is otherwise expected to be of ~2 log units in an iron-free melt: The increase in the fugacity ratios of H2O/H2 due to degassing upon decompression is restricted by H2 produced during oxidation of ferrous iron by water. The importance of this "Le Chatelier effect" strongly depends on the fO2 conditions prior to degassing.
V31C-0605
Rapid Quench Cold-Seal Apparatus with Computer-Controlled Pressure and Temperature Cycling
We have constructed two computer-controlled, rapid quench, hydrothermal apparatuses that are ideal for experimentation on volcanological, geothermal, and ore deposit research problems. The devices can achieve maximum pressures of about 2 kbar and temperatures to 1100C, have the ability for experiments to be quenched very rapidly in a water-cooled environment, and are interfaced with computers which can control any regimen of pressure and/or temperature cycling that may be desired, accomplished via Lab-View software and data acquisition and motion control boards from National Instruments. The rapid quench aspects of the design were developed originally by Dr. Phil Ihinger and have subsequently been adopted by many labs around the world; a good summary description of these aspects of the equipment, and the use of filler-rods for controlling redox conditions in such equipment, are provided by Matthews et al. (2004, Am. Mineral., 88: 701-707). Our design has fixed Rene 41 pressure vessels, furnaces that are raised and lowered by computer controlled pneumatic cylinders and water cooling systems that are controlled by computer operated solenoid valves. The novel feature of our design is the pressure generation and control systems. We coupled the seal-ends of commercially available (HIP) pressure generators to shop-built linear actuators consisting of nearly frictionless ball lead screws within thick walled stainless steel housings. These in turn are driven by NEMA size 23 stepper motors coupled to 100:1 gear reduction units. The actuators require 21 revolutions to achieve their full stroke of 12.7 cm which displaces about 10 cc of fluid. Operating the motors at the relatively low resolution of 800 steps per revolution leads to about 132,000 steps per cm of travel of the pressure-generating piston, providing exceptionally high precision and excellent pressure control. Instantaneous decompression can be achieved by simply opening a valve while motor-controlled decompression from 2 kbar to 1 bar can occur over time spans ranging from about one minute to months. This equipment will find immediate use in studies of decompression- induced magmatic vesiculation and crystallization in sub-volcanic and volcanic conduit environments and decompression-induced precipitation of fracture-filling ore and silicate minerals in crustal hydrothermal environments.
V31C-0606
Experimental Constraints on Ar and Ne Solubility in H2O-CO2 Bearing Basaltic Melts
Although noble gases are only trace components of magmatic volatile phases, generally dominated by H2O and CO2, they represent a powerful tool to study the degassing behavior of ascending magmas. Current models of noble gas degassing from magmas use theoretical values of noble gas solubilities, because experimental measurements in hydrous melts are very rare. Here we report an experimental study of Ar and Ne solubilities in anhydrous and H2O-CO2 bearing basaltic melts. The starting material was represented by an Etnean lava erupted in 2002. High pressure experiments were performed at superliquidus temperature (1200°C) and pressures of 1-3 kbar in internally heated pressure vessels. Investigated volatile phases were represented either by Ar or Ne (open capsule experiments) or by Ar, Ne, H2O and/or CO2 (sealed capsule experiments). In sealed capsule experiments the charged amounts of volatiles were computed to have a H2O-CO2 dominated vapor, with noble gases as minor species (partial pressure of a few bars), similarly to natural magmatic systems. Rapidly quenched glasses have been analyzed by electron microprobe (major elements), FTIR spectroscopy (H2O and CO2), bulk extraction and quadrupole mass spectrometry (noble gases). Ne and Ar molar fractions in the vapor were calculated by mass balance considering loaded and dissolved aliquots of volatiles. In some cases, the capsule was directly opened in an ultra-high-vacuum line and the pressure of each volatile was measured by a vacuometer, cryogenically separating the species. Experimental Ar solubility is comparable to the theoretical one predicted by the IP model, while Ne solubility results much higher. The effect of water on Ar and Ne solubility is in agreement with the predictions by the EIP model: increasing concentrations of dissolved water decrease the Henry's constant values for both Ar and Ne. Nonetheless, the model overestimates the intensity of the water effect on Ar solubility. The theoretical model has been therefore refitted to the experimental data. The obtained results can be directly employed for a reliable modeling of noble gas degassing from Etnean melts. The adopted experimental setting avoids any extrapolation and/or assumption deriving from the use of experimental data achieved in conditions unlike those of natural magmatic systems.
V31C-0607
Lherzolite-saturated melt compositions of peridotite MM3: results of near-solidus micro- sandwich experiments
Results of the 1 GPa diamond-aggregate melting experiments of Baker and Stolper (1) and Baker et al. (2) on the peridotite composition MM3 continue to be controversial (3,4), especially regarding the observation (1,2) of high SiO2 and low TiO2 contents of partial melts produced near the solidus. Here we present the results of four 1 GPa micro-sandwich experiments on MM3 at near-solidus temperatures of 1245-1250°C. As in our earlier experiments (1,2), the MM3 mix consists of natural olivine, orthopyroxene, clinopyroxene, and spinel grains that are less than 15 microns in size. Four different synthetic glass compositions were used and all lie off the compositional trends defined by the MM3 partial melts in oxide vs. MgO space (1,2,5). Experimental charges were constructed by placing a small chip of synthetic glass (0.4-0.8 mg) within a much larger mass (13-14 mg) of powdered MM3; each combined glass-MM3 sample was run in a graphite crucible within a sealed Pt capsule for 122 to 144 hr in a piston cylinder apparatus. At P and T, the initial glass chip within a charge generates a small pool of liquid whose composition shifts as it equilibrates with the MM3 solid phase assemblage. If the near- solidus MM3 partial melting trend of (1,2,5) is correct, then experiments with different initial glass compositions will produce final liquids that are consistent with this compositional trend. Except for TiO2 vs. MgO in one experiment, the final glasses all lie within 1-2 sigma of the oxide vs. MgO trends defined by the partial melts of MM3 (1,2,5). Note, that by minimizing the amount of basaltic glass added to MM3 in each experiment (mass fractions varied from 0.03-0.06), the glasses do not substantially perturb the bulk composition of the starting peridotite, which minimizes the need for iterative sandwich experiments (e.g., 6). We also compared the liquid compositions from both the peridotite melting experiments and traditional sandwich experiments of (4; done using a synthetic oxide mix of MM3) with our data (1,2,5). The two data sets overlap at the 1-2 sigma level when liquid compositions are plotted as a function of liquid MgO content and thus, contrary to the claims of (4), the two data sets are consistent with each other. The divergence of the two data sets when liquid compositions are plotted as a function of temperature reflects the increasing concentration of K2O, P2O5, H2O, and Cl in the partial melts of (1,2) compared to the liquids of (4), whose synthetic bulk compositions were K2O, P2O5, and Cl-free. Results of our micro-sandwich experiments lend support to the partial melting trend of (1,2,5) on MM3, especially with regard to the high SiO2 and low TiO2 contents in liquids at low degrees of partial melting.(1) Baker and Stolper (1994) GCA 58, 2811-2827; (2) Baker et al. (1995) Nature 375, 308-311; (3) Falloon et al. (1997) EPSL 152, 149-162; (4) Falloon et al. (1999) JPet 40, 1343-1375; (5) Hirschmann et al. GCA 62, 883-902; (6) Robinson et al. (1998) EPSL 155, 97-111
V31C-0608
xMELTS: A thermodynamic model for the estimation of magmatic phase relations over the pressure range 0-30 GPa and at temperatures up to 2500 C
A thermodynamic model for multicomponent silicate liquids in the system SiO2-TiO2-Al2O3- Fe2O3-Cr2O3-FeO-MgO-CaO-Na2O-K2O-P2O5-H2O is calibrated over the pressure range 0-27.5 GPa and temperature range 700-2500°C from previously published experimental data (LEPR, http://lepr.ofm-research.org) on liquid-solid phase equilibria. The liquid model is combined with thermodynamic models for relevant igneous solid solutions - including a new model for majoritic garnets - to facilitate the calculation of phase relations by minimization of thermodynamic potentials. Extension to high pressures is achieved by adopting the liquid EOS of Ghiorso (2004, AJS 304, 637-838) and the Universal EOS for solid phases. The Gibbs free energy of the liquid is described as a regular associated solution, which permits a more physical description of the configurational entropy. The model includes both the speciation of water as molecular and hydroxyl units and multiple species of oxidized iron. The latter makes possible an internally consistent description of melt redox equilibria over the oxygen fugacity range from the iron- wüstite buffer to air. The model is calibrated from approximately 20000 statements of phase equilibria, including 6100 between endmember components of clinopyroxene and liquid, 3550 between olivine and liquid, 2800 orthopyroxene-liquid, 2750 feldspar-liquid, 2200 spinel-liquid, 950 garnet-liquid, 350 liquid-rhombohedral oxide (largely ilmenitess), 650 statements of water saturation, and a host of miscellaneous phases coexisting with liquid, importantly quartz, leucite, nepheline, (Mg,Fe2+)-perovskite, and (Mg,Fe2+)- wüstite. Calibrant liquids span naturally occurring compositions, but do not include data on simple systems (e.g., CMAS). xMELTS supersedes MELTS (Ghiorso and Sack, 1995, CMP 119, 197-212) and pMELTS (Ghiorso et al., 2002, G3 10.1029/2001GC000217) for the calculation of magmatic phase equilibria from crustal conditions down to the base of the transition zone of the Earth's mantle.
V31C-0609
Sugar-Mineral Interactions and the Origins of Life
Sugars may have been necessary for the origin of life, specifically in the initial abiological synthesis of RNA. One possible mechanism sugars could have formed on the primitive Earth is the formose reaction, the base-catalyzed polymerization of HCHO. This reaction provides a plethora of sugar products, none of them in particularly high yield relative to the others. Ribose, and its derivative deoxyribose, are the only sugars used in biological nucleic acids, if the formose reaction or something similar was responsible for the initial synthesis of sugars for biology, there must have been some mechanism by which ribose was selectively concentrated in the environment. It is hypothesized that stereochemistry of sugar molecules and their interaction with surrounding minerals may have provided one such mechanism. A formose solution was synthesized through the polymerization of formaldehyde. A technique was developed for the fluorescent derivitization of these sugars using dansyl-hydrazine. The derivitized sugars were then analyzed using an HPLC with UV-vis and fluorescence detection. To see if mineral-sugar interactions could provide some selectivity during fluid migration, formose mixtures were run through mineral columns (CaCO3 or beach sand (mostly quartz)) and the eluant was analyzed. There did appear to be some mild differences in the migration patterns of the various components. Since formose reactions typically must occur in concentrated solution, whereas the bulk concentration of HCHO in the primitive oceans was likely rather low, the eutectic synthesis of sugars, both in the presence and absence of Al2O3 and CaCO3, was performed to determine whether HCHO can be concentrated and reacted via this mechanism. This research provides a procedure for further study of mineral and sugar interactions.