AN INVESTIGATION OF THE STABILITY OF NICKEL-BEARING MINERALS IN ULTRAMAFIC-HOSTED HYDROTHERMAL VENT SYSTEMS
Rachael Hoover (University of Colorado) and Dionysis Foustoukos
A possible explanation for why life can thrive in extreme conditions, such as hydrothermal vents, is the presence of hydrocarbons. In ultramafic-hosted hydrothermal systems, synthesis of abiogenic hydrocarbons has been suggested to occur through the following processes: a)serpentinization, which promotes elevated concentrations of H2(aq):
Olivine + H2O → Serpentine + Brucite + Mgt + H2(aq)
and b) reduction of CO2(aq) or CO(aq) to short chain hydrocarbons:
CO2(aq) + [2 + (m/2n)] H2(aq) = (1/n) CnHm(aq) + 2 H2O
In the case of a homogeneous system, carbon reduction has been shown to produce low yields of hydrocarbons. However, vent fluid samples collected from ultramafic-hosted hydrothermal systems along mid-ocean ridges, such as Rainbow or Lost City at the Mid-Atlantic Ridge, are enriched in short chain hydrocarbons (Proskurowski et. al 2008). Thus, a number of experimental studies have been conducted to investigate the role of mineral catalysts in promoting formation of organics by Fischer-Tropsch Type synthesis. From the whole range of mineral phases evaluated, the most efficient catalyst for methane synthesis has been widely accepted to be native Ni and the Ni-Fe alloy; awaruite (Horita and Berndt, 1999). Our project investigated the stability of nickel and nickel-bearing minerals under hydrothermal conditions and compared experimental data to theoretical models. The current models published by Klein and Bach (2009) show that in order for awaruite to be present, highly reducing conditions need to be established. Based on our current knowledge or serpentinization reactions this is not feasible and therefore awaruite must be stable at less reducing conditions (i.e. low H2(aq) concentrations). The main hypothesis of our study was that thermodynamic data of awaruite are incorrect and this can have a profound effect on phase equilibria between Ni-bearing sulfides (i.e. heazlewoodite, pentlandite) and awaruite. A series of hydrothermal experiments has been conducted involving, magnetite, heazlewoodite and a composite of native Ni, Fe (80:20) coexisting with 3.2 wt% NaCl aqueous solution at 400°C or 200°C and 500 bars. Dissolved volatile concentrations (H2, H2S) were measured with gas chromatography and the final mineral phases were identified by using a scanning electron microscope. Preliminary results clearly indicate presence of awaruite at less reducing conditions than those proposed in theoretical studies. Accordingly, peridotite alteration at elevated temperatures can render stable Ni and Ni-bearing metals, promoting in this way the abiotic synthesis of hydrocarbons during seawater hydrothermal circulation.
UNDERSTANDING THE CAUSE OF OUR OXYGENATED ATMOSPHERE
Breana Hashman (Dickenson College) and Dominic Papineau
Approximately 2.45-2.32 billion years ago the Earth’s atmosphere became oxygenated, allowing for a radiation of biological evolution. Around this time, the Earth also experienced major glaciations, tectonic rifting, and one of the largest δ13C excursions in history; the Lomagundi-Jatuli event. Data was collected that tested the hypothesis that weathering of phosphates and subsequent blooms of primary productivity in the oceans would cause an increase in atmospheric O2. This model explains not only an increase in atmospheric oxygen, but also the cause of the major δ13C isotope excursion in carbonates due to the large amount of organic material burial that takes place with high primary productivity rates. Using δ13C excursions as a proxy of primary productivity, and phosphorus concentrations to show the presence of rate limiting nutrients, the hypothesis of the project was that phosphorus would be linked with δ13C excursions. Samples were analyzed from 15 distinct localities in the Aravalli Supergroup, NW India. δ13C values were collected using a gas bench linked to a Delta XL IRMS. Phosphorus data was collected using a modified colormetric method developed by Murphey and Riley, 1962. Phosphorus and δ13C excursions were found together in five of the localities, but the other ten basins had phosphorus bearing rocks without the presence of δ13C excursions. However, no definite conclusion can be found regarding the hypothesis until δ13C values for organic carbon have been collected, because previous literature has found excursions in δ13C organic data when it was absent in δ13C carbonate data.
UNDERSTANDING THE PREBIOTIC SYNTHESIS OF OROTATE AND URACIL
Rachel Maxwell (University of Arizona) and George Cody
The subject involving the origin of life is as much geochemical as biological. The question that remains unanswered is how and where life could have possibly originated if the Hadean earth did not have a concentrated reservoir of useful organic molecules. One possible pathway to the synthesis of organic molecules is through the abiotic reduction of carbon dioxide. The energy released from these redox reactions becomes available for the synthesis of organic molecules which evolve and become autocatalytic by forming metabolic cycles. Theoretical calculations have stated that the reduction of carbon dioxide to form organic molecules is thermodynamically favored in hydrothermal vent systems. In this set of experiments, we focused on the synthesis of orotate and uracil. These molecules are both important building blocks of life. Orotate and uracil are synthesized naturally occurring through the addition of carbamoyl phosphate reacting with aspartic acid. Carbamoyl phosphate is a highly reactive molecule and it releases energy to remove the phosphate group during its pathway to synthesize uracil. We conducted a series of experiments to see if orotate and uracil could be synthesized via a urea addition to fumaric acid. We wanted to investigate whether an elevated pressure, similar to those in hydrothermal fluids, would enhance orotate synthesis. Solutions were prepared ranging in different concentrations of urea, fumaric acid, and ammonium hydroxide. These solutions were either heated in an oven or run in a hydrothermal apparatus to simulate temperatures and pressures equivalent to those found in hydrothermal fluids. Once the mixtures had reacted the results were analyzed using GC-MS and LC-MS. When the experiments were completed it was observed that (1) higher concentrations of urea correlate to higher yields of orotate, (2) as pressure increased the yield of orotate decreases and the yield of carbonate increases, and (3) that there is a direct relationship between the synthesis of carbamate and n-carboxyl-aspartic acid. The problem happened to be that urea is unstable under hydrothermal conditions. The results show that the synthesis of orotate starting with the reactants urea and fumaric acid can occur in hydrothermal fluids but the yield suffers due to the hydrolysis of urea. If this route is the most likely abiotic route to orotate it would require protection of urea, from water, perhaps through the development of a hydrophobic environment, e.g. abiologic “ooze,” or a layer of non-polar hydrocarbons that would likely cover all exposed surfaces.
TRACE AND MINOR ELEMENT ANALYSIS OF MOLYBDINITE
Melissa McMillan (University of Arizona) and Robert Hazen
To enhance the mineral evolution framework proposed by Hazen et al. (2008), trace and minor element analyses were collected on the mineral phase molybdenite (MoS2) to explore the existence of trends in composition over geologic time. Molybdenite may prove to be a useful case study as a consequence of its presence in Earth’s early history and its possible coevolution with biology via its role in the nitrogen fixation enzyme nitrogenase. Fifty molybdenites were collected from the Smithsonian National Museum of Natural History and correspond to 35 locations worldwide. The ages of the samples span 2.5 billion years and were obtained by publications corresponding to the location of their formation. The electron microprobe was used to test for Fe, W, Re, Mn, Cd, Cu, Ni, and V, but Ni, Cd, and V were determined to be absent. Trace amounts of Mn and Cu were observed on the order of 100 ppm for both. Larger amounts of Fe, W, and Re were detected on the order of 100 ppm up to 4000 ppm. Lack of homogeneity in Fe concentrations was observed throughout samples, suggesting the presence of pyrite inclusions rather than an incorporation of the element in the molybdenite crystal structure. Analyses were examined as a function of time, and results show that the samples containing high concentrations of W and Re formed within the last billion years. The trends of W and Re may reflect a delay in the incorporation of an oxygenated atmosphere into the Earth’s crust since the Great Oxidation Event at ~2.4 Ga. The enrichment of oxygen in continental material would allow for increased oxidation of W and Re, and may have possibly allowed for increased availability and addition to the molybdenite crystal structure. Further analyses must be obtained before a definitive hypothesis is proposed.
HIGH-PRESSURE CRYSTAL CHEMISTRY OF NORBERGITE
Amanda Lindoo (Augustana College) and Stephen Gramsch
Norbergite and other humite minerals are important in ultra-high pressure metamorphic (UHPM) terrains, where it is debated if they are the source of ilmenite exsolution. In our study we addressed the possible role of pressure in the exsolution process, with a focus on the humite group. Our goal was to observe the polyhedral change in response to increasing pressure to identify a structural discontinuity, which may assist the exsolution process. The crystal structure of norbergite was examined using single crystal x-ray diffraction analysis up to 8.5 GPa. Zigzag-type octahedral chains running parallel to the c-axis are the main features of the orthorhombic structure. Pressure was increased from ambient to 2.5, 4.5, 6.5 and 8.5GPa yielding R-values of 3.7, 6.5, 3.8, and 5.9%. Norbergite unit cell parameters were refined by least-squares methods using 15-20 reflections. Atomic positions were rendered in the CrystalMaker program to observe polyhedral distortions occurring with increasing pressure. Between 4.5 and 6.5 GPa it was found that the edge-sharing octahedral chains buckle or dramatically distort. Pressure-volume data for the mineral also suggests a change in the compression mechanism around these pressures. The structural discontinuity found in our study may assist the exsolution process. Though it is the more complex members of the group that are found in these terrains, we can hypothesize that the compression behavior seen in norbergite may continue on and occur at lower pressures. If so, this find would be consistent with previous pressure estimates for UHPM around 3-4GPa. Powder diffraction data on norbergite was also collected at station 16-ID-B (HPCAT) at the Advanced Photon Source, Argonne National Laboratory, at 5.6, 14.8, 18.3, and 20.0 GPa, to investigate the possibility of a structural transition at higher pressures suggested by lattice enthalpy calculations carried out with the GULP code. As pressures rose, the diffraction pattern changed dramatically with the introduction and departure of peaks over this pressure range. Our data reflects a possible phase transition in norbergite around 15 to 20 GPa.
THE DISSOLUTION OF CARBON DIOXIDE IN SODIUM SILICATE MELT AT 15 KBARS AND 1400 °C
Kathryn Kumamoto (Williams College), George Cody, and Bjorn Mysen
Volatile compounds dissolved in melts strongly affect the chemical and physical properties of the melt. By studying the dissolution mechanisms of such compounds, the chemical speciation of the volatile in the melt can be characterized. In order to determine dissolution mechanisms for carbon dioxide in a sodium-silicate melt, glass samples were synthesized and analyzed for carbon speciation. In these studies, samples were prepared from a mixture of 13C-enriched silver oxalate and sodium-silicate glass with a sodium-to-silicon ratio of 0.5. The experimental conditions for all melt samples were the same: 15 kilobars of pressure and a constant temperature of 1400 °C for 90 minutes. The glasses were then analyzed with Raman spectroscopy and 13C-NMR in order to characterize the immediate local environment of the carbon species within the glass. Four levels of oxygen fugacity were studied by using four different buffers: magnetite-hematite, nickel-nickel oxide, magnetite-wüstite, and ironwüstite. It was found that under the oxidizing conditions of magnetite-hematite and nickel-nickel oxide, carbon was dissolved as a networked carbonate, which confirmed previous experimental observations. Under the reducing conditions of magnetite-wüstite and ironwüstite, carbon was dissolved as methane and methyl groups bonded to silicon. The observation of the presence of methyl groups bonded to silicon is a new finding for this class of systems. In addition, the Raman spectra confirmed that water was present in all the melts to varying degrees and that reduced hydrogen in the form of H2 was present in the reduced samples.
SEISMOLOGY: THERE'S AN APP FOR THAT
Benjamin Horkley (Woodrow Wilson High School) and Steven Golden
Seismic measurements are often done in remote areas, accessible only a few times per year. A typical stand-alone seismic station consists of the seismometer and a data logger, which records the data to attached disk drives for later collection by a field crew. During station visits, field personnel control the data logger through a handheld device to check its status, and change its configuration if necessary. One widespread seismic data logger is the RT130 by REFTEK Inc., which is traditionally controlled through REFTEK’s proprietary software running on a Palm handheld device. While this software functions well, compatible Palm handhelds are not produced anymore, and we felt that its user interface still offered room for improvement. Therefore, we developed a new RT130 control application, named AcquiControl, which runs on Apple’s iPhone or iPod Touch, and features a redesigned, user-friendly interface. While the Palm handheld communicates with the data logger through a serial cable, the iPhone or iPod Touch connects to it wirelessly. This is made possible through a wireless “dongle” attached to the data logger’s serial port. AcquiControl demonstrates the possibility of creating a third-party application to interface with data loggers in the field. Planned future work includes the expansion of the application to cover all capabilities of the older Palm software and beyond. In particular, the application could be adapted to support other data loggers than the RT130, giving the user a similar interface across different models. Also, recording parameters could be synchronized with a centralized database to ease the preparation of seismic metadata.
STUDYING THE UPPER MANTLE THROUGH THE UNDERSIDE REFLECTIONS: AN INVESTIGATION OF THE X DISCONTINUITY
Byron Kelly (Memorial University of Newfoundland) and Nicholas Schmerr
The X discontinuity is a proposed upper mantle discontinuity, lying at a depth of 250-350 km and associated with volcanic hotspots and active or old subduction zones. This boundary is characterized as a 1-2% impedance contrast with a thickness of 5-10 km, and is proposed to be due to coesite to stishovite transition. Using underside reflections collected from the High Lava Plains broadband seismometer array, we surveyed the subduction zone of western South America, the central Pacific, including the Hawaii hotspots, and the Kuriles subduction zone. Through our analysis, we discovered that precursor reflections from the X discontinuity are rarely observed in each of these regions, with only 5% of all high quality event records containing energy appropriate for an X discontinuity. Hence, we conclude that the X is not a laterally continuous discontinuity of the upper mantle. Instead, we propose that observations of the X are due to the reflections of small, perhaps lens shaped compositional anomalies within the upper mantle. This feature generates an impedance contrast significant enough to produce small amplitude reflections, which are seen as small amplitude precursors to underside reflections on migrated and stacked event records. Further, we propose that these packages are significantly smaller than the Fresnel zone of underside reflections, which is on the order of 1000-2000 km. Due to the small size of the lenses, the majority of underside reflections would not sample the resulting X discontinuity. Techniques such as ScS reverberations, receiver functions, or P’P’ precursors, which each have a Fresnel zone much smaller than that of underside reflections, would more appropriately sample the X discontinuity.
HD 34700: AN UNUSUAL SPECTROSCOPIC BINARY
Jennifer Moses (Franklin & Marshall College) and Alycia Weinberger
HD 34700 is widely considered to be a young spectroscopic binary with a circumstellar disk around the binary. Variation of the H-a lines had been previously reported, which could be indicative of accretion. We extracted and analyzed spectra that were taken during several nights of the binary’s orbital period. We used several IRAF routines in order to conduct this investigation. We found that the H-a lines do not differ much with time, and that the shape is not indicative of accretion. Rather, the H-a spectra appear to have an inverse P Cygni profile indicative of infall and this could lead to better understanding of the environment around HD 34700. We then used three years of imaging data processed with software created by Guillem Anglada to determine the parallaxes and proper motions of HD 34700 and other stars in the same field. The parallax of HD 34700 was based upon the assumption that the background (or “reference”) stars had a parallax of 0. This initial calculation provided us with a rough estimate of the distance to our object of interest, which was around 300 parsecs, but this is a lower limit to the distance. Work was then done to fine-tune the parallax of HD 34700 by determining the distance and true parallax of the reference stars. This was done by using an IDL routine to fit a stellar model to magnitudes taken from catalogs such as NOMAD and 2MASS. The model was used to determine an effective temperature as well as a normalization to the stellar brightness, a value that was equal to luminosity times the distance squared. Using a polynomial fit of the main sequence, the temperatures of the stars were used to determine a true luminosity. Using this luminosity with the earlier output value, distance to the reference stars could be determined. Overall, this work will add to the knowledge of HD 34700, giving better insight to the characteristics of the system. One motivation for studying systems such as this is to determine if planets can form around a binary. This work may lead to other projects that will make that determination.
A HIGH-PRESSURE STUDY OF THE NH3-H2 SYSTEM TO 13 GPA
Bethany Chidester (University of Toledo) and Timothy Strobel
Hydrogen is of particular interest as it is the most abundant element in the universe and its simplicity is archetypal to condensed matter physics. Molecular hydrogen (H2) has been studied extensively under pressure as a lone entity and in conjunction with other simple molecules. The NH3+H2 system is applicable to a number of research areas including hydrogen storage and the formation of novel hydrogen-bonded clathrate structures, the electronic structure of hydrogen-dominant materials, ammonia-rich planetary bodies, and the fundamental understanding of intermolecular interactions at high density. In this study we compressed three different compositions of hydrogen and ammonia in a diamond anvil cell to 13 GPa at 300K. We analyzed these samples using Raman spectroscopy and synchrotron x-ray diffraction. We report that there is a small amount of mutual solubility in the fluid phases, but after 1 GPa and up to 13 GPa they tend to remain phase separated. Two phase transitions in ammonia and one in hydrogen were observed, all of which occurred at pressures comparable to those of the pure substances. A preliminary phase diagram is given, as well as diffraction patterns and an equation of state.
WATER-CARBON DIOXIDE MIXTURES UNDER EXTREME CONDITIONS
Donald Plattner (Centre College) and Maddury Somayazulu
In situ high pressure-temperature Raman spectroscopy was used to investigate the formation of clathrates in a H2O-CO2 mixture and to study the chemical interactions between water and CO2 at supercritical conditions. Diamond anvil cells were loaded with ruby, water, carbon dioxide, with a gold plated gasket used for the sample chamber. Quartz was later added to the cell as a pressure sensor for supercritical phase analysis. At 25 °C and within the pressure range of 0.8 to 2.6 GPa no clathrate was observed. Our results confirm recent findings which also dispute claims of clathrate existence at these conditions. A decrease in the temperature required to reach the supercritical phase was observed a pressure range of 0.4 GPa to 4.5 GPa. Furthermore, at a pressure of 4.4 GPa and a temperature of 290 °C, a chemical reaction occurs between carbon dioxide and water which causes pressure to decrease by 0.4 GPa. The new compound has a peak with a frequency shift of 1000 cm-1. This reaction and the compound it produces are of great interest and are currently being investigated.
MEASURING THE THERMAL CONDUCTIVITY OF ARGON AT HIGH PRESSURE AND TEMPERATURE
Michael Wong (University of California - Berkeley) and Alexander Goncharov
Accurate data on the thermal conductivity of argon at high pressures and temperatures is essential to unraveling the deep and mysterious nature of the Earth’s interior. Argon is a common pressure-transmitting medium in diamond anvil cells experiments, which is the preferred method for studying the properties of minerals at pressures and temperatures native to the mantle and core. Using a recessed gasket to hold an iridium coupler inside argon, we load a diamond anvil cell and bring it up to 50 GPa in increments of a few GPa. Pulsed laser heating pumps thermal energy into the coupler, which then conducts heat into the argon. We determine the temperature of the coupler by applying the Planck function to its thermal emission spectrum, and doing this over time yields temperature verses time for the coupler. We then use a computer program to simulate this experiment. After inputting the parameters of our diamond anvil cell and the thermal properties of diamond and iridium, we make an educated guess for the thermal conductivity of argon based on theoretical calculations. The output of this iterative program gives temperature verses time of the coupler. By fitting our experimental data to the theoretical model, we should be able to soundly determine he thermal conductivity of argon.