MR43B-1229 

High pressure melting of Cu under hydrostatic and shock wave loading

Han, L), University of Science and Technology of China, University of Science and Technology of China, Hefei, Anh 230026, China An, Q), University of Science and Technology of China, University of Science and Technology of China, Hefei, Anh 230026, China An, Q), California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, United States Xie, Y), University of Science and Technology of China, University of Science and Technology of China, Hefei, Anh 230026, China Zheng, L Q), Florida State University, Florida State University, Tallahassee, FL 32306, United States Tschauner, O), University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154, United States * Luo, S N (sluo@lanl.gov), Los Alamos National Laboratory, Los Alamos National Laboratory, Los Alamos, NM 10504, United States

We investigate high pressure melting of single crystals of Cu under hydrostatic and shock wave loading using molecular dynamics simulations. The equilibrium metling curve is established via aolid-liquid coexistence and by using the superheating-supercooling hysteresis method, and is found to be in agreement with experiments and independent simulations. Shock wave loading is conducted along 100, 110, and 111, for which different metling behavior is observed: Typical superheating-melting is found for 110 and 111, respectively. A minor degree of premelting is seen for shock loaded crystals oriented along 110. The stress tensor at shock state manifests hydrostaticity above 50 to 70 GPa. These results underline the necessity for cautious interpretation of shock wave loading with respect to phase transitions and material strength.

MR43B-1230 

Structural Evolution of Schreibersite, Fe3P, at High Pressure

* Howard, J (jwhoward@unlv.nevada.edu), Department of Physics, University of Nevada, Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4002, United States Sinogeikin, S (ssinog@hpcat.aps.anl.gov), HPCAT,Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Ave., Argonne, IL 60439, United States Nicol, M), Department of Physics, University of Nevada, Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4002, United States Tschauner, O (olivert@physics.unlv.edu), Department of Physics, University of Nevada, Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4002, United States Tschauner, O (olivert@physics.unlv.edu), Division of Geological & Planetary Sciences, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, United States

Fe3P schreibersite is an abundant mineral in iron meteorites. Previous work [Scott et. al., Geophys. Res. Lett. (2007) 34, L06302/1-5] reported a phase transition occurred in a powder sample of Fe3P schreibersite above 17 GPa at ambient temperature, but did not identify the structure of this high pressure phase. This high pressure phase is not quenchable to ambient pressure, however, the transition and its reversion may induce characteristic twinning in schreibersite crystals, which may be identified in meteoritic material and, thus, help to constrain shock pressures for iron meteorites. By using a diamond anvil cell with a methanol/ethanol pressure medium to generate pressure, the structure of single crystal Fe3P was studied by X-ray diffraction up to 30 GPa (at room temperature) at end station 16 ID-B of the Advanced Photon Source. Our experiment indicates that the phase transition occurs around 10 GPa and appears to suggest that the material twins during compression. Acknowledgement: The authors thank the HPCAT team for their help, and U.S. DOE Cooperative Agreement No. FC08-06NA27684 with UNLV for supporting the work. Portions of this work were performed at HPCAT (Sector 16), APS, ANL. HPCAT facility is supported by DOE-BES, DOE-NNSA, NSF, and the W.M. Keck Foundation. The APS is supported by the U. S. DOE-BES under Contract No. W-31-109-Eng-38.

MR43B-1231 

Dynamic loading of silica glass: elasticity, plasticity, fracture, and phase changes

Xie, Y), University of Science and Technology of China, University of Science and Technology of China, Hefei, Anhui, Hefei, Anh 230026, China An, Q), University of Science and Technology of China, University of Science and Technology of China, Hefei, Anhui, Hefei, Anh 230026, China An, Q), California Institute of Technology, 1200 E. Calfornia Blvd., Pasadena, CA 91125, United States Han, L B), University of Science and Technology of China, University of Science and Technology of China, Hefei, Anhui, Hefei, Anh 230026, China Zheng, L Q), Florida State University, Florida State University, Tallahassee, FL 32306, United States Xia, K), University of Toronto, University of Toronto, Toronto, ON ON M5S 1A4, Canada Tschauner, O), University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154, United States * Luo, S N (sluo@lanl.gov), Los Alamos National Laboratory, Los Alamos National Laboratory, Los Alamos, NM 10504, United States

We investigate the mechanical and physical properties of silica glass under high strain rate dynamic loading using molecular dynamics simulations. Several loading methods are explored: planar and spherical shock waves, as well as one- and trhee-dimensional loading at constant strain rates. Elastic and plastic deformation is examined as function of both, strain rate and initial temperature. Fragmentation and spall processes are quantified and linked to classical nucleation theory and the Grady damage law. The rich phenomena of phase changes occurring under loading and unloading are examined. Silica structures are analyzed in terms of RDF, structure factors, density of states, ring size, and bond angle distributions.

MR43B-1232 

A petrographic study of shocked minerals from the Vredefort Dome, South Africa

* Quintero, R R (raizaquintero@gmail.com), University of Puerto Rico, PO Box 9017, Mayaguez, PR 00681, Puerto Rico Cavosie, A J (acavosie@uprm.edu), University of Puerto Rico, PO Box 9017, Mayaguez, PR 00681, Puerto Rico

The effects of impact-induced shock metamorphism can be preserved in the microstructure of individual mineral grains in target rocks, and thus provide a record of past impact events. This undergraduate research project is a petrographic study of shock metamorphism preserved in minerals from the Vredefort Dome impact structure, South Africa, with the goal of documenting shock features using standard petrographic techniques. The Vredefort Dome is widely regarded as the oldest and largest preserved impact crater on Earth at 2.02 Ga (Kamo et al., 1996 EPSL), and is thus important in studies of impact processes on the Precambrian Earth. Five samples representing three rock types were collected from the Vredefort Dome: two different quartzites were sampled from the collar zone, including Dominion Group quartzite (Ro) on R53 north of Parys, and quartzite Rjo1 on the maps of Bisschoff (1999). In addition, three granitoids were sampled, including two pseudotachylite breccias, from the center of the dome. Two pseudotachylite samples from quarries within the amphibolite zone contain granitoid clasts; a third sample of granulite-facies granitoid (charnockite) was collected from the amphibolite-granulate transition near Vredefort. In general, all of the samples are quartz-rich, and exhibit quartz grains with variably developed planar deformation features (PDFs). Two and three compelling sets of PDFs within individual grains were only observed in quartz from the collar zone; most samples contain quartz with only one set of conspicuous PDFs, usually decorated, that are readily visible with optical light microscopy. Shock microstructures were also observed in accessory minerals, including zircon. Detrital zircons in quartzite (unit Ro) contain PDFs that are readily apparent with a 10x to 40x objective. The zircons are average size (e.g. 125 microns), and contain parallel PDFs with an apparent regular spacing of 5 microns. Zircons were observed in all granitoid and pseudotachylite samples, however no grains with PDFs have (thus far) been observed, although Kamo et al (1996) report zircons from Vredefort pseudotachylite that contain PDFs. In addition to zircon, a single grain of apatite was observed in the Ro quartzite with possible PDFs. The grain is average size, 135 x 50 microns, and contains one dominant set of parallel fractures that are less-regularly spaced than in zircon, and are oriented 72 degrees from parallelism with the c- axis. While the identification of PDFs in apatite from Vredefort Dome is tentative, apatite has previously been described with shock microstructures from other impact sites (French, 1998).

MR43B-1233 

Wadsleyite and ringwoodite formation from melt induced by a shock event in Peace River L6 chondrite

* Miyahara, M (miyahara@ganko.tohoku.ac.jp), Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ward, Sendai, 980-8578, Japan Goresy, A E (Ahmed.Elgoresy@uni-bayreuth.de), Bayerisches Geoinstitut, Universität, Bayreuth, Bayreuth, D-95440, Germany Ohtani, E (ohtani@mail.tains.tohoku.ac.jp), Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ward, Sendai, 980-8578, Japan Ferroir, T), ENS-Lyon, Lyon, Lyon, 69364, France Gillet, P), ENS-Lyon, Lyon, Lyon, 69364, France Nagase, T), Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ward, Sendai, 980-8578, Japan Nishijima, M (ni_shi@imr.tohoku.ac.jp), Institute for Materials Research, Tohoku University, Sendai, Sendai, 980-8577, Japan Vashaei, Z), Institute for Materials Research, Tohoku University, Sendai, Sendai, 980-8577, Japan

The assemblages of wadsleyite and ringwoodite transformed from individual olivine contained in a deformed chondrule were identified in the shock melt veins of Peace River L6 chondrite. The assemblages of wadsleyite and ringwoodite were extracted by using a FIB system, and analyzed by TEM/STEM-EDS. There was obvious enrichment or depletion in Mg and Fe ratios between ringwoodite (Fo = 66) and wadsleyite (Fo = 89). Using the interdiffusion coefficients in order to check if the contrasting compositions of ringwoodite and wadsleyite, respectively could have resulted from solid-state interdiffusion alone leads to unrealistically long duration of the shock event. Few stacking faults were observed both in ringwoodite and wadsleyite thus suggesting that both minerals didn't form by a shear mechanism. The deformed chondrules are squeezed and flattened implying strong plastic deformation and partial melting. There is no evidence of mixing of melts of olivine and clinopyroxene, the latter not melted. It is considered that wadsleyite and ringwoodite successively crystallized from individual melts of the former olivine crystals alone. Wadsleyite, low in Fe, crystallized first from melt in the interior of the former olivine crystals followed by Fe-rich ringwoodite nucleating on wadsleyite thus separating it from the residual melt enriched in Fe.

MR43B-1234 

Shock Metamorphism of L6 Chondrites Sahara 98222 and Yamato 74445: the P-T Conditions and the Shock age

* Ozawa, S (ozawasin@ganko.tohoku.ac.jp), Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan Ohtani, E (ohtani@mail.tains.tohoku.ac.jp), Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan Suzuki, A (a-suzuki@mail.tains.tohoku.ac.jp), Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan Miyahara, M (miyahara@ganko.tohoku.ac.jp), Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan Terada, K (terada@hiroshima-u.ac.jp), Department of Earth and Planetary System Sciences, Hiroshima University, Higashi- Hiroshima, 739-8526, Japan Kimura, M (makotoki@mx.ibaraki.ac.jp), Institute of Astrophysics and Planetary Science, Faculty of Science, Ibaraki University, Mito, 310-8512, Japan

Impact phenomena are the fundamental processes of accretion of the terrestrial planets. Therefore, investigations of meteorites that experienced shock events are useful for understanding mechanisms of planetary impact events and formation of terrestrial planets. Heavily shocked meteorites contain abundant shock melt veins, where some high-pressure minerals have been discovered. In this study, we investigated mineralogy of shock melt veins of two L6 chondrites (Sahara 98222 and Yamato 74445) and estimated the P-T conditions during their impact events.We found that the shock melt veins of these meteorites contain several high-pressure minerals such as wadsleyite, jadeite and tuite for Sahara 98222 and ringwoodite (+ wadsleyite), akimotoite and lingunite for Yamato 74445. Tuite is a high-pressure polymorph of whitlockite and lingunite is a high-pressure polymorph of albite with hollandite structure. Based on mineralogy in the shock veins; we estimated the pressure and temperature conditions during their impact events: 13-15 GPa, > 2000°C for Sahara 98222 and 15- 24 GPa, > 2200°C for Yamato 74445, respectively.We also conducted a U-Pb dating of phosphates in and around the shock melt veins of Sahara 98222 using a Sensitive High Resolution Ion Micro Probe (SHRIMP-II) at Hiroshima University to reveal when this shock event occurred. We obtained following radioactive ages: Pb-Pb isochron age: 4466 ± 31 Ma; U-Pb isochron age: 4498 ± 150 Ma; Total U-Pb isochron age: 4467 ± 22 Ma. These ages seem to be slightly younger than the previously reported ages of chondrites, which are usually older than 4500 Ma. This could suggest that Sahara 98222 have recorded a shock event in the very early stage of the solar system where the planetary formation was going on.

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.