Rebecca Peretz-Lange, MS - US grants

This award provides 50% of the funds required for the purchase of a differential scanning calorimeter and a dilatometer/viscometer that will be housed and operated in the Department of Geological Sciences at the University of Michigan. The University of Michigan is committed to providing the remaining funds necessary for this equipment acquisition. The equipment is to be used for the measurement of heat capacity and other thermodynamic and transport properties of silicate minerals and liquids of interest in research on the chemical and physical processes taking place in the Earth's crust and mantle.

The proposed research will elucidate the relationship between density and coordination changes of Al3+, Fe3+ and Ti4+ in silicate melts. Experiments are designed to obtain precise measurements of melt density using the double-bob Archimedean method over a range of compositions and temperatures at a pressure of one bar. The proposed density measurements will complement information on melt structure obtained by NMR, Raman and IR spectroscopy. Properties such as density, and the factors that affect them, are fundamental in studies of magma evolution - - they affect melt segregration at the source region, magma ascent through diapirs and fractures, and the processes that produce chemical diversification in magmas.

9405768 Lange This award will support experiments to measure the denisty and compressibility of hydrous silicate liquids between 900- 1600 oC and 1-20 kbars. Measurements will be performed on NaAlSi3O8, KAlSi3O8, and rhyolitic liquids containing 1-10% H2O and will be based on the floating and sinking of ultra- pure crystalline graphite buoyancy markers. The experiments outlined will allow direct determination of the partial molar volume of water in silicate melts as a function of temperature and pressure.

9508133 Lange Despite the overwhelming evidence for the role of carbonatite melts as metasomatic agents in the mantle, the physical properties of these melts are poorly constrained. Although carbonatite melts are known to have extremely low viscosities, their density and compressibility (particularly as a function of composition) are completely unknown. The research goal of this study is to provide the first direct measurements of density, thermal expansion and compressibility on a wide variety of multicomponent (CaCO vya1 3-MgCO3-FeCO3-SrCO3-BaCO3-Na2CO3-K2CO3) melts over a wide range of temperature (1000-17000oC) and pressure (0-35 kbars). After developing a model equation appropriate to this seven-component system, experiments will be extended to carbonatite liquids containing dissolved SiO2, P2O5, and F. The long-term teaching goals include: the active recruitment, advising and support of undergraduates to pursue research for a senior thesis; teaching an upper division, required petrology course that allows the students to practice the application of calculus and thermodynamics to big-picture, tectonically-related problems of magmatism and metamorphism; teaching summer filed camp each year; development of a new introductory course that will demonstrate why a knowledge of geology has implications for understanding the political and economic structure of a developing country, like Mexico. vya1

9526338 Lange This grant awards $16,610 as one-half of the costs of acquiring equipment necessary to construct a rapid-quench, cold-seal pressure apparatus for experimental petrological research to be conducted at the University of Michigan. Specifically, the system will be used to synthesize volatile-bearing silicate liquids at low pressures (<300 MPa). These samples will then be used for low- temperature (<1000 degrees C) measurements of density, thermal expansion, viscosity, and heat capacity. In situ density (sink/float) and viscosity (falling sphere) experiments will also be conducted using volatile-bearing silicate liquids. These experiments will allow precise determination of the partial molar volume of water and other volatiles in silicate melts. ***

9706075 Lange This project involves experiments to measure the density, thermal expansivity and compressibility of H2O-bearing magmatic liquids between 400 and 1300oC and from 1 bar to 2000 MPa. Two approaches will be taken: (1) low temperature density measurements of hydrous liquids at their glass transition temperatures, and (2) the sinking and floating of ultra-pure crystalline graphite and commercially carbon-coated quartz, albite, and anorthite buoyancy markers in a rapid-quench cold-seal pressure apparatus between 50-200 MPa and a piston cylinder apparatus between 600-2000 MPa. The results will have application to problems of melt segregation and migration from source regions and the dynamics of melt degassing and fragmentation during explosive magmatic eruptions.

9903070
Lange

This grant provides partial support of the costs to acquire an ultrasonic acoustic interferometer for the High Pressure and Temperature Laboratory at the University of Michigan. This instrument will be used to measure the compressibilities of multicomponent silicate liquids. The ultra-high temperature capability of the apparatus (> 2000 degrees centigrade) will allow access to a wide range of melt compositions, including those with high liquidus temperatures (e.g. peraluminous liquids, molten peridotite) and those that are too viscous to obtain relaxed sound speeds below 1600 degrees centigrade (e.g. molten rhyolite). Constraints on the temperature dependence of melt compressibility will be substantially improved by measuring relaxed sound speeds over temperature intervals spanning several hundered degrees. The interferometer will also be used at lower temperatures on volatile-bearing liquids (containing fluorine and phosphorous) and a variety of carbonatite liquids under conditions where it is established that volatile loss does not occur. An additional application is to examine variations in the compressibility of silicate melts undergoing composition-induced coordination change of cations (Al3+, Fe3+, and Ti4+) at one bar. These experiments will provide analogies for understanding the consequences of pressure-induced coordination change of these cations on melt density. In addition to the P.I., Rebecca Lange, other faculty at the University of Michigan who are likely to utilize the equipment in their research include Associate Professors Youxue Zhang and Lars Stixrude. This will be the first acoustic interferometer that is capable of ultra-high temperature work on liquids and is thus likely to attract outside users throughout the U.S.

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9815351
Zhang
This award supports Drs. Youxue Zhang and Rebecca Lange and two postdoctoral or graduate students from the University of Michigan in a collaboration with Francois Holtz and Harold Behres of the Institute for Mineralogy at the University of Hannover, Germany. The research funded by this award will focus on thermodynamic and transport properties of silicate melts and glasses, especially as affected by dissolved H2O. Understanding the effects of dissolved H2O in silicate melts on such properties as viscosity, density, crystallization temperature, and diffusivity is critical to a complete understanding of geological processes. Because of the complementary expertise and facilities of the German and U.S. groups, and their interest in different aspects of the same research problems, this collaboration will be of great benefit to both sides. The research program will investigate many new areas of collaboration that will increase our knowledge of geological and volcanic phenomena.

9911352
Essene

This award provides 67 percent partial funding support for the acquisition of a new electron microprobe to be installed in the Department of Geological Sciences at the University of Michigan. The University is committed to providing the remaining funds necessary for the acquisition. The new microprobe will be operated as part of the University of Michigan's Electron Microbeam Analytical Laboratory, ensuring adequate technical support and access for all campus researchers. The electron microprobe is an analytical tool that focuses a beam of energetic electrons on a sample surface, generating characteristic X-rays from the elements in the sample. The technique produces precise chemical composition analyses of unknown samples with good spatial resolution in the micron range. Anticipated applications at the University of Michigan include research in earth sciences, science of materials, chemistry, engineering and dentistry.
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Lange
9909567
The goal of grant EAR-9909567 is to take advantage of recent improvements in the precision and automation of 40Ar/39Ar geochronology to perform an intensive dating program of Quaternary volcanic products along the western Mexican volcanic arc. In addition, we will use field measurements and topographic maps to quantify the volume of magma erupted over the last 1 Myr. The climate and infrastructure within this 200 km arc segment, render it among the best in the world for accurately quantifying the volume of erupted magma over this time period. Our primary aim is to obtain a quantitative history of the eruptive flux, in terms of the volume and relative proportion of magma type erupted along the strike of the arc. We will test whether the volcanic output varies as a function of crustal thickness, rate of slab subduction, age of subducted slab, and degree of lithospheric extension.

Lange
EAR-0087764

The primary goal of this proposal is to measure the zero pressure compressibility of a variety of silicate liquids over a wide temperature range using an ultrasonic acoustic interferometer. Our high-temperature capability will be used to: (1) obtain relaxed sound speeds on liquids that are too viscous for such measurements below 1600 degrees C (e.g., dacite and rhyolite), (2) access melts with exceptionally high liquidus temperatures (e.g., peraluminous melts, komatiite, peridotite), and (3) improve constraints on the temperature dependence of melt compressibility by measuring relaxed sound speeds over temperature intervals that span several hundred degrees. In addition, experiments are planned to examine variations in the compressibility of silicate melts undergoing composition-induced coordination change of cations (Al3+, Fe3+, Ti4+) at one bar. These experiments will provide analogies for understanding the consequences of pressure-induced coordination change of cations on melt density. A final application is to silicate melts containing volatile components (fluorine and phosphorous) and a variety of carbonatite liquids. All of the proposed sound speed measurements at zero pressure (one bar) will provide a critical complement to in-situ methods that allow density and compressibility to be derived at pressure.

Lange
EAR-0310079

A major challenge to modeling the partial melting process at deep mantle depths is the lack of information on the density of magmatic liquids at high pressure. The largest uncertainty is with the pressure dependence on melt compressibility (K0' = dK0/dP), and how K0' varies with melt composition. The goal of this proposal is to tightly constrain values of K0' for four silicate (NaAlSi3O8, CaTiSiO5, Na2Si2O5, K2Si2O5) and three carbonate (Li2CO3, Na2CO3, K2CO3) liquids that are highly compressible at one bar (KT,0 between 4 and 17 GPa at 1600 degrees C). These results, when combined with K0 and K0' data in the literature will provide a robust test of the hypothesis that the K0' of a silicate liquid is inversely correlated with its one-bar bulk modulus (K0). If this new hypothesis is verified, it will allow the K0' of magmatic liquids to be estimated from their one-bar bulk modulus, for which there are well-calibrated models. Conversely, if the postulated relation between K0 and K0' is shown not to hold, the new K0' data for silicate and carbonate liquids will substantially augment the existing data set for liquids for which K0' is known independently of K0. The method that we will use to determine liquid K0' is fusion curve analysis, combined with high-quality phase-equilibrium experiments. This project will provide training to two female graduate students in X-ray diffraction, FTIR spectroscopy, and electron microprobe analysis, as well as with high-pressure and high-temperature equipment including a cold-seal pressure vessel and piston-cylinder apparatus. It will also provide them with an education in thermodynamic calculations of crystal-liquid equilibria, and on the importance of their results to studies of magmatism and volcanism. The skills that they will develop will prepare them equally well for a career in either the earth sciences or the high-tech materials industry.

This project, jointly supported by the Petrology and Geochemistry (EAR) and the Americas Programs (INT, is to perform an intensive 40Ar/39Ar dating study, coupled with quantitative estimates of erupted volumes, to fully characterize the volcanic history of three large central volcanoes in western Mexico and their surrounding peripheral vents. This proposed study would extend coverage of the total volcanic output (= 1 Ma) along a continuous 200 km arc segment, which is crucial in addressing global questions regarding the role of different subduction parameters on the eruptive output at arcs. In addition, new data on the eruptive history at individual volcanic fields significantly enhances geochemical and petrological data sets and allows more robust tests of the mechanisms and timescales for magma differentiation. The results of our proposed 40Ar/39Ar dating program will assist in the creation of volcanic hazards maps (independently, by Mexican scientists) in the proposed study area, which is the site of at least six, highly-explosive eruptions in the last 1 Myr, all from vents within = 40 km of Tepic, the capital of the state of Nayarit. Our collaboration with Dr. Hugo Delgado-Granados, from the Universidad Nacional Autonoma de Mexico (UNAM), has led to an extensive exchange of expertise and facilities between the University of Michigan and UNAM, as well as a series of student field trips that alternate between the U.S. and Mexico every other year. This project will provide training to two Ph.D. students (one female/one male), who will become skilled in Ar chronology, volcanic petrology, field mapping, and GIS (Geographic Information System) software tools.

An equation of state (P-V-T relation) for magmatic liquids is critical for quantitative models of partial melting and melt transport beneath spreading ridges and subduction zones, where oceanic and continental crust are formed. A major challenge to thermodynamic models of partial melting in the deep mantle is the lack of information on the density of magmatic liquids at high pressure. The largest uncertainties are with the pressure dependence to melt compressibility and with how volatile components affect melt density at high pressure. The primary objective of this proposal is to measure the compressibility and density of numerous geologically relevant liquids as a systematic function of pressure and temperature, using a frequency-sweep acoustic interferometer in an internally heated pressure. These data will provide a quantitative link between the microscopic structure of liquids, obtained from spectroscopic studies, and their macroscopic properties. Thus these data will greatly enhance the utility and insights provided by different spectroscopic tools and molecular modeling within the earth and material sciences. The sound velocity data on melts at high pressure will also be helpful for improved interpretation of seismic velocity variations in the crust and mantle, where partial melt may be present. Graduate students will be partially supported by this grant. The interdisciplinary nature of the training that they will receive is excellent preparation for either an academic career in the earth sciences or an industry career involving high-tech materials.

EAR-0447113
Lange

The goal of this project is the development of a high-pressure acoustic interferometer that can be used to measure the sound speed and density (and thus compressibility) of silicate liquids in an internally heated pressure vessel (IHPV). We plan to develop two different techniques at elevated pressure: (1) the frequency sweep method to measure liquid sound speed, and (2) the reflection coefficient method to measure liquid density. We will use an existing IHPV that is operable to 0.3 GPa and 1200 degrees celsius. Funds from this grant will be used for various equipment and machine shop costs and to partially support a full-time technician. Measurement of the density and compressibility of silicate liquids at high pressure is a major experimental imperative in the earth sciences, especially when applied to volatile-bearing melts. These data are needed for accurate thermodynamic calculations of crystal-melt and fluid-melt equilibrium at depth, which in turn are required for quantitative models of partial melting, melt transport, crystallization and degassing, and the mechanics of magma eruption. The graduate students involved in this project will obtain a strong background in thermodynamics, acoustics and signal processing, as well as petrology and geochemistry. It is anticipated that the techniques that we develop will become widely used throughout the ultrasonics and earth sciences community.

This award was co-funded by the Americas Program (Office of International Science and Engineering), and the Petrology and Geochemistry program (Division of Earth Sciences) in order to provide support to offset the costs for young Latin American and U.S.scientists (including graduate students and postdoctoral fellows) to participate in two Geochemistry meetings in south-central Chile that will address first-order questions bearing on arc magmatism and volcanism: (1) the 2007 State of the Arc (SOTA) meeting, and (2) a Geological Society of America (GSA) Field Forum to the Tatara-San Pedro volcanic complex. Many Latin American countries are located along subduction zones, and are subject both to the hazards and benefits that arise from them. The volcanic and plutonic exposures in these countries have been the focus of intense international research on all aspects of subduction zone processes. It is also known that almost a third of the Quaternary arc volcanoes around the Pacific Rim are located in Mexico, Central America, and South America. The purpose of the 2007 SOTA meeting is to critically examine the state of knowledge regarding arc magmatism and volcanism. The purpose of the GSA Field Forum is to bring together researchers from around the world to visit one of the most spectacularly exposed, yet young (925 ka to the Holocene) volcanic complexes in the world, which has been intensively studied over the last 20 years.

The primary goal of this award will be to enable young Latin American and U.S.scientists (including senior graduate students and postdoctoral fellows) to attend the two meetings, meet with one another, and thus initiate and foster long-term collaborative relationships. Funds to support the participation of U.S. graduate students will ensure that the next generation of researchers will be educated to see the benefit of international scientific cooperation at an early stage in their careers. The small size of the meetings (70-90 for SOTA and 32 for the GSA FF) is especially conducive to substantial and extensive dialogue between different groups, which is critical to the formation of viable, international partnerships in the future.

The goal of this proposal is to provide the first measurements of various thermodynamic properties (heat capacity, density, thermal expansion, compressibility) for a wide range of liquids in the MgCO3-FeCO3-CaCO3-Na2CO3-K2CO3-Li2CO3 system. These fundamental thermodynamic data for carbonate liquids, especially those containing CaCO3 and MgCO3, will permit thermodynamic models of partial melting for carbonate-bearing mantle rocks. Such models are needed to rigorously evaluate the complex global carbon cycle, which includes the subduction of carbonated oceanic crust, the formation of carbonatite melts that metasomatize diverse mantle lithologies, the partial melting of these carbonated rocks, and the subsequent volcanic outgassing of CO2 to the atmosphere. Thermodynamic property measurements on multi-component carbonate liquids are of interest not only to earth scientists, but also to material scientists interested in molten carbonate fuel cells to derive energy from hydrogen.

We plan to add 10-50 mol % CaCO3 and MgCO3 (and 10-30 mol % FeCO3) to various mixed alkali (Li-Na-K) carbonate liquids with low melting temperatures, and to perform measurements of heat capacity (by differential scanning calorimetry; DSC), density (by the double-bob Archimedean method), and sound speed (by acoustic interferometry) to obtain melt compressibility. An additional objective is to perform a series of phase equilibrium experiments to locate the fusion curves of various carbonate phases (e.g., K2Ca(CO3)2, Na2Ca(CO3)2, Na2CO3, CaCO3, MgCO3, KLiCO3, etc.) in P-T space. From these two sets of experimental data, we propose to use fusion curve analysis to constrain the enthalpies of fusion of the various carbonate phases as well as their respective liquid values (the pressure dependence of their melt compressibility).

This research is a highly coordinated, multi-lab, collaborative effort to measure the density and compressibility of magmas that form during melting in the Earth's interior. The measurements will greatly advance our ability to predict the conditions under which magmas will rise buoyantly to the Earth's surface and erupt as lavas or form volcanoes. The measurements will also reveal the conditions and depths where magmas are too dense to rise to the surface, remaining either trapped by neutral buoyancy, or sinking further into our planet's deep interior. The experimental data will also provide new insight into the way in which the Earth was differentiated into crust, mantle, and core during its primordial formation stage. The collaborative effort combines experimental techniques that span the entire range of pressure and temperature conditions that exist for melting and magma production in the Earth. The highest pressures, simulating the deepest regions of Earth's mantle, will be done under dynamic compression at the Caltech Shockwave Laboratory, the intermediate pressures will be carried out under static compression in large presses at the University of New Mexico's High Pressure Laboratory, and the near-surface magmatic conditions will be studied in high temperature furnaces with ultrasonic techniques at the University of Michigan's Experimental Petrology Laboratory.

The new data will lead to the development of an empirically-based equation of state and a model for multicomponent silicate melts. This model should allow precise characterization of the locations of crystal/melt density crossovers in the upper mantle, transition zone, lower mantle, and D" layer. This equation of state will be used in models of differentiation of a whole-mantle magma ocean or in defining the chemistry and dynamics of possible silicate melting at the modern core-mantle boundary. The investigators expect that the data will also provide the essential basis for development of next-generation melt models that encompass explicit speciation and/or non-ideal mixing terms. The data gathered under this proposal will be a precious resource for all future studies of melt properties and igneous differentiation at high pressure. Never before have such a wide range of techniques been applied to a common set of samples; together the complementary data sets will significantly enhance our understanding of magma physics within our planet.

Rhyolite is the most differentiated silicate magma type on Earth and makes up some of the largest explosive eruptions (100-1000's km3), including those that have occurred at Yellowstone National Park. Understanding the origin and evolution of large-volume rhyolitic magmatic systems is of considerable interest because their formation must fundamentally reconstitute and differentiate continental crust, and they are candidates for future "supervolcano" eruptions. The mineral phases in rhyolites often provide a rich opportunity to examine pre-eruptive temperatures, oxidation states, and melt water concentrations, as well as time scales for melt accumulation in the upper crust. However, there is a surprising paucity of phase-equilibrium experiments on natural rhyolite melt compositions, which limits the potential to use these mineral phases to extract the maximum amount of information.

The goal of this proposal is to perform hydrous phase-equilibrium experiments in a cold-seal and piston-cylinder apparatus under controlled oxygen and water fugacity (fO2 and fH2O) conditions on a variety of natural rhyolite liquids over a range of temperature and pressure, which will enable calibration of the plagioclase-liquid hygrometer to rhyolite compositions. The experiments will also be used to determine trace element partition coefficients between mineral and melt, particularly for Sr and Ba. The partitioning behavior is critical to understanding how extremely low-Sr rhyolites form, some of which constitute some of the largest (most voluminous) explosive eruptions on Earth. Finally, these experiments will greatly enhance the calibration of broad thermodynamic models of crystal-melt equilibrium, which when combined with geophysical models can provide a deeper understanding of how large-volume rhyolite magma bodies form and why they sometimes erupt explosively, which is a significant geohazard.

Water plays a unique role in the planetary evolution of Earth, particularly at subduction zones. The recycling of oceanic water into the mantle at subduction zones, the tectonic setting where continental crust forms, triggers partial melting and the formation of hydrous basalts, which differentiate to form continental crust, unique to Earth within our solar system. One of the many challenges associated with the study of hydrous basalts is that current thermometers cannot be accurately applied to them. The goal of this project is to calibrate a Ni-based olivine-melt thermometer, which is independent of melt water contents and can thus be applied to hydrous basalts to obtain accurate temperatures of formation. It will also allow the concentration of water in basaltic liquids to be determined at the onset of crystallization. This project will engage two Ph.D. graduate students and at least three undergraduate students, who will be trained in the operation of various experimental apparatus and analytical techniques, as well as thermodynamic modeling; all of these tools and skills have important applications in material science. The project will support students from underrepresented groups in a research team that has demonstrated a commitment to expanding the diversity of those in the sciences.

The specific goals of this proposal are to perform hydrous phase-equilibrium experiments in a cold-seal apparatus under controlled fO2 and fH2O conditions on a variety of natural basalt and basaltic andesite liquids over a range of temperature and pressure, which will enable calibration of how these parameters, together with melt composition, affect the partitioning of Ni between olivine and liquid. In addition, the depression of the olivine liquidus as a function of melt water content (up to ¡Ü 8 wt%) will be experimentally mapped out for several melt compositions. Once a well-calibrated thermometer and hygrometer are in hand, it will be applied to >100 basalts from the Mexican and Cascades volcanic arcs and compared to results from olivine-hosted melt inclusions. Two additional experimental goals are to measure crystal growth rates of olivine phenocrysts under hydrous melt conditions, especially for natural samples that contain olivine with diffusion-limited growth textures, and to test whether Fe-Mg KD values obtained in hydrous olivine-melt experiments can be used to place constraints on the oxidation state of natural basalts.