MR13B-1704
Impact agglomeration of silica and Cu nanoparticles
Impact agglomeration has supposedly played a key role in the formation of planetesimals. Here we examine the agglomeration of nanoparticles as an extreme case, which is also interesting for developing physics- based scaling laws across nanometer to geological scales. The nanoparticles tend to coalesce spontaneously as driven by their high surface energy. However, the rate of agglomeration can greatly facilitated via impact. We conduct molecular dynamics simulations on two representative systems to illustrate this point: silica and Cu. Impact of silica and Cu nanoparticles is simulated in the binary and ternary systems as a function of impact velocity/angle and particle size. Our preliminary results show that agglomeration rate increases with the impact velocity, and varies with the impact angle. However, fragmentation occurs when the impact velocity exceeds a critical value. The morphology and structure of nanoparticles during impact are also characterized.
MR13B-1705
Fe2SiO4-rich spinel as mineral in a shocked meteorite - constraints on P-T conditions during shock
We report the occurrence of a spinel phase (Fe0.8, Mg0.2)2(Si0.9, Fe0.1)O4 in veins of the L4 chondrite Laundry West, Nullarbor, Australia. While Fe2SiO4-rich spinel has been reported from the Umbarger meteorite earlier (Xie et al. Am .Min. 87, 1257, 2002), the present study is the first to present complete structural and chemical information. We collected powder diffraction, EBSD, and EMP data, all confirming structure and chemistry of this new mineral, the Fe-endmember analog of Mg2SiO4 ringwoodite. The observation of this spinel phase, which forms at pressures of a few GPa under static conditions, in a shocked meteorite is a contribution to a finer shock metamorphic scale. The vicinity of these FeSi-spinel grains to melted (Fe,Ni)S in combination with modeling of shock reverberation in a FeS-silicate system allows for estimating a lower limit of the peak shock pressure and temperature: The fayalite-spinel P-T phase boundary and the melting curve of (Fe,Ni)S determine a fixed point in P-T space of 5-6 GPa and 1500 – 1600 K. However, the bulk shock pressure (and temperature) was lower and can be calculated by impedance match. Acknowledgements: We dedicate this work to our friend and collaborator Thomas J. Ahrens. We are particularly grateful to Dr. Zhongwu Wang, CHESS, for providing beamtime and support at station B2. This work was supported by NNSA Cooperative Agreement DOE-FC88-01NV14049 and NASA/Goddard grants under awards NNG04GP57G and NNG04GI07G. Participation by NK was supported by the Caltech SURF program and in particular by Mr. and Mrs. Robert E. Anderson.
MR13B-1706
High-pressure behavior of iron-nickel-cobalt phosphides and its implications for meteorites and planetary cores
Minerals with composition (Fe,Ni)xP, are rare, but important accessory phases present in iron and chondrite meteorites. The occurrence of these minerals in meteoritic samples is believed to originate either from the equilibrium condensation of protoplanetary materials taking place in solar nebulae or from crystallization processes in the cores of parent bodies. Fe-Ni phosphides are considered an important candidate for a minor phase present in Earth's core, and at least partially responsible for the observed core density deficit with respect to pure Fe. We report results of high-pressure high-temperature single-crystal X- ray diffraction experiments with end-members belonging to the (Fe,Ni,Co)2P family, including Fe2P, Ni2P and Co2P. A new phase transition to the Co2Si-type structure (allabogdanite) has been found in Fe2P barringerite at 8.0 GPa, upon heating. The high-pressure phase can be quenched metastably to ambient conditions and then, if heated again, it transforms back to barringerite. Ni2P barringerite does not undergo transformation to allabogdanite structure up to 50 GPa, but instead exhibits incongruent melting with formation of pyrite-type NiP2 and Ni-P glass. Our results indicate that the presence of allabogdanite in meteoritic samples places two important constraints on the thermodynamic history of the meteorite. First, it imposes a minimum pressure and temperature for the formation of the Fe2P, and additionally rules out any higher temperature low pressure alterations. If present in the Earth's core, Fe2P will have the allabogdanite rather than the barringerite structure. Crystal chemical trends in the compressibility of (Fe,Ni,Co)2P minerals, as well as polymorphic transition paths are analyzed in the context of Earth and planetary core composition and properties.
MR13B-1707
Compositional Variation and Homogenization Kinetics of Serpentine in Hydrous alteration processes of Carbonaceous chondrite parent body: An Experimental study under reducing conditions
Carbonaceous chondrites are the most primitive planetary materials which consist of various disequilibrium assemblages of minerals derived from various stages of the early solar system. Especially, hydrous phyllosilicate minerals in CM chondrites are the first products of aqueous alteration on the meteorite parent body, and those show huge compositional variation. The main mineral species of the hydrous phyllosilicate minerals in CM chondrites are serpentine, saponite and tochilinite. Compositional variation involving homogenization processes in the phyllosilicate minerals may have essential information on the timescale of the aqueous alteration processes on the parent body. In this study, we carried out aqueous alteration experiments of heterogeneous starting materials with fluid containing ethanol to keep reducing conditions representative to the early solar system remaining the solar nebula gas. We have carried out aqueous alteration experiments of synthetic olivine (Fo55) with synthetic fayalite or enstatite. Fo55 olivine represents the Mg/ (Mg + Fe) molar ratio of the solar abundance. Fayalite or enstatite represents Fe-rich or Fe-poor components in the heterogeneous parent body, respectively. Experimental fluids are ethanol solutions with 0.5, 2.5 or 10.0 vol. %. Decomposition of ethanol supply reducing agent to the fluid and keep the oxidation condition of the system on the C-CO buffer. Experimental temperatures are 100, 150, 200, 250 and 300°C with vapor pressure, and 400 and 500°C with 100MPa.Run durations are 3 to 12 weeks. Run products are analyzed by XRD and SEM / EDS. Aqueous alteration experiments of Allende meteorites show that Mg / Fe compositions of serpentine in the run products with higher temperatures show broader distribution to Mg-rich composition than that of 200°C experiments. Mg-rich olivine derived form chondrules contribute to produce serpentine in higher temperature. Mg / Fe composition range of serpentine is getting narrower with run duration (Isobe and Ozaki, 2008). Quantitative kinetics of the evolution and compositional variations of the phyllosilicate produced in the aqueous alteration from the heterogeneous starting materials will be discussed.
MR13B-1708
Searching for the Origins of Extraterrestrial Matter
A relatively significant amount of Insoluble Organic Matter (IOM) is contained within chondritic meteorites. Although the chemical structure of this IOM has been analyzed, questions still speculate as to what molecule(s) and chemical reactions it has resulted from. The carbonaceous chondrite, Murchison, was analyzed with NMR spectroscopy revealing the abundance of furan and aromatic carbons in its chemical structure. With the formose reaction as a guideline, formose products were created using formaldehyde and glycolaldehyde in order to create products that could potentially be structurally similar to the IOM found in carbonaceous chondrites. Using NMR spectroscopy to analyze the chemical structure of these products, they were found to contain many of the same functional groups as the IOM from Murchison. The main difference was the increased amount of methine carbon present in the formose products, which also led to a lower amount of aromatic carbon than the Murchison. A possible solution to decrease the amount of methine is to find a way to dehydrogenate the formose products; therefore, increasing the amount of aromatic carbons due to creation of double bonds from the dehydrogenation mechanism. Overall, the formose reaction can still be considered to be a possible reaction pathway for the synthesis of primitive IOM. Further studies into how these organics evolved through chemical reactions will be able to yield more insight into some of the most primitive chemistry taking place in our galaxy.
MR13B-1709
Using ArcGIS for correlating multi-technique micro-spatial analytical data: A case study of early solar system carbonates in a carbonaceous chondrite.
Meteorites are rare and valuable extraterrestrial materials that are typically studied using multiple micro- and nanoanalytical techniques such as SEM, EPMA, SIMS, SXRF and FIB/TEM. Each of these techniques is frequently used to study the same thin section in detail. Management of the significant amounts of spatial and analytical data obtained at various scales from the millimeter to nanometer-scales over a ~3 cm2 thin section is a major challenge. Here we demonstrate that a geographical information system, or GIS, typically used for much larger scale spatial data manipulation can be used equally successfully to store and analyze spatially correlated petrographic and mineralogical data. The advantages of using GIS techniques at the microscale are multifold. For example, querying various types of analytical data can be made with ease by the researcher. Furthermore, posted geodatabase meteorite data can be analyzed by other researchers concurrently or years after a project has been completed. This facilitates comparisons between other meteorite samples of differing classification, within a classification, or samples of the same meteorite. Here we demonstrate the application of a GIS to a correlate data obtained from a thin section of the ALH84051 CM1 meteorite, a carbonaceous chondrite that has experienced extensive aqueous alteration. Mosaiced images obtained by optical microscopy of the entire thin section are used as a base "map" and are overlain with SEM and CL images obtained at different magnifications, compositional data (EPMA), and other spatial data. The overall objectives of this study are to gain insights into the processes of aqueous alteration using carbonate mineral assemblages, morphology, abundance, and chemical composition (major, minor and trace elements). Future work will also include Mn-Cr chronometry and oxygen isotopic analysis using SIMS to examine carbonate emplacement and fluid evolution within the meteorite parent body.
MR13B-1710
Fe/Mg-Fe/Mn Systematics of Chondrules and Effect of Chondrule Forming Event.
Chondrules generally show wide range of chemical properties which can be attributed to several processes (e.g. evaporation, condensation and metal/silicate fractionation) occurred during high temperature chondrule forming event and low temperature secondary events (e.g. igneous fractionation) on parent body. To find out which process had maximum impact, we examine the relation between Fe/Mg and Fe/Mn for the individual chondrules in Semarkona (LL3.0), Chainpur (LL3.4), Allende (CV3) and Renazzo (CR2) chondrites. Significant variation of Fe is observed for most chondrules and Renazzo shows the largest range. Chondrules show different trend (mostly depleted in Fe) compared to their host chondrites. CAIs in Allende fall in Mn/Mg chondritic range and show distinct trend on Fe/Mg vs. Fe/Mn plot and lesser variation in Fe compared to chondrules. Relative to CI, chondrules show depletion in Mn relative to Mg, which can be attributed to loss of Mn due to volatility controlled fractionation. Among chondrules and CAIs in Allende, chondrules are more depleted in Mn relative to Mg. This is understandable as chondrules have experienced longer duration of heating, resulting in higher fractionation of Mn. Some chondrules in Semarkona and Chainpur show higher Mg/Mn ratio, indicating effect of igneous process like crystallization. Chainpur chondrules reveal negligible or no effect of secondary alteration as they overlap with Semarkona chondrules. Chondrules in LL chondrites and Allende fall in different regions. This suggests significantly different precursors for them. Variation in Fe is the major effect on the chondrules and this can be attributed to either heterogeneity in chondrule precursors or metal/silicate fractionation (mainly loss of metal/sulfide) during chondrule formation. It is also possible that both the reasons are responsible. Study of CR2 chondrules with larger Fe variation can be useful for further examination.
MR13B-1711
Oxygen Isotopic Measurements of Calcite Grains in a Refractory Inclusion by Nano-SIMS: Implications to The Formation Process of Carbonate in the Early Solar Nebula
Refractory inclusions (CAIs) from chondritic meteorites are widely considered to represent the first materials that formed in the solar nebula (MacPherson et al. 1988). We discovered for the first time a unique spherical CAI, which consist of calcite, spinel, diopside and PCP from Murchison meteorite. Inside of this refractory inclusion, calcite, spinel, diopside coexist each other and include abundant vacancies. Calcite is always surrounded by diopside and spinel. Direct evidence for in situ formation of the secondary phases, such as veins, is totally absent. Replacement is not also recognized. The oxygen isotopic data are plotted into two distinct regions on three isotopic diagram. The primary phases of spinel and diopside have typical 16O-enriched values of -40 to -50 ‰, while calcite are plotted 16O-riched values of -5 to -20 ‰ on the CCAM line. The degree of 16O-enrichiment of spinel and diopside is similar to those in non-altered CAIs of CV chondrites. The 16O-riched values of calcite do not support the model such as alteration products in the meteorite parent body after CAI solidification. Our result indicates that calcite formed initially 16O-rich region similar to most of refractory objects. Therefore, We think that the calcite in this refractory inclusion should be already formed in the early solar nebula. In fact, carbonate is usually attributed to aqueous alteration in solar system objects (on Earth or in meteorites). A recent study suggests that carbonate may form in the presence of water vapor in solar type proto-stars (Ceccarelli et al. 2002). The detection of calcite in solar type proto-stars, where no liquid water has existed, represents a new frontier in carbonate formation theories. The textual occurrences and isotopic evidence of calcite in this refractory inclusion are clearly compatible with such a report.
MR13B-1712
Chemical Composition Measurement of Cosmic Dust from Impact Generated Plasmas
In-situ chemical analysis of cosmic dust is possible due to hypervelocity impact ionization. Upon impact on a solid surface, a dust grain is vaporized and partially ionized. Mass analysis of the atomic or molecular ions is used to reveal the chemical composition of the dust. There are past and currently operating dust impact analyzer instruments on the Stardust and Cassini spacecrafts, for example, but the need remains for laboratory calibration measurements to aid the interpretation of the mass spectra. A set of measurements is presented using dust samples of cosmic interest, electrostatically accelerated to relevant velocities and detected with a novel diagnostic instrument. The measurements are performed at the Heidelberg dust accelerator facility, where dust particles are accelerated to up to 50 km/s. The instrument used for the calibration is the prototype version of the recently developed Large Area Mass Analyzer (LAMA), which combines large active target area with high mass resolution.
MR13B-1713
High-pressure properties of diamond (carbon) from shock-wave experiments to 10 Mbar.
The physical behavior of carbon at high pressure, particularly in the diamond phase, is important in planetary settings including terrestrial impact events and the deep interiors of carbon-rich giant planets such as Neptune, and in the laboratory where diamond-anvil cells are used to study the high-pressure behavior of materials. Here, we report recent data on the high-pressure and high-temperature properties of carbon obtained using shock-wave compression experiments on single-crystal diamond. Specifically, we have studied the intrinsic two-shock structure in diamond for shock compression in the 100, 110 and 111 crystallographic orientations. We have examined the limit of the purely-elastic response of diamond, experimentally determining its yield strength. We have measured the equation-of-state and shock Hugoniot of diamond, finding significant deviation from the previously reported shock measurements of Pavlovskii (1971). We have directly observed the melting temperature of diamond at high pressure, and have studied the optical properties of diamond as it transitions from a transparent solid at ambient conditions to a metallic liquid at high pressure and temperature.