Prem P. Phakey

Bio: Prem P. Phakey is an academic researcher from University of California, Los Angeles. The author has contributed to research in topics: Transmission electron microscopy & Recrystallization (metallurgy). The author has an hindex of 2, co-authored 2 publications receiving 368 citations.

Shock processes in porous quartzite: Transmission electron microscope observations and theory

Abstract: A high-resolution study of shocked Coconino Sandstone from Meteor Crater, Arizona, was undertaken using transmission electron microscopy to investigate the textural relations of high-pressure phases produced by meteorite impact In weakly shocked rocks (estimated average pressure, P < 100 kb), quartz in the interiors of grains retains its initial microstructure, but near original grain boundaries, quartz is altered by fractures and planar features resembling Brazil twins, and is partially transformed to coesite and glass In moderately shocked rocks (estimated average pressure, 100 < P <250 kb), as much as 50% of the residual quartz is fractured but otherwise undeformed Near grain boundaries relatively undamaged quartz exists in direct contact with coesite and stishovite Filamentary, microvesicular “froth” fills cracks and fractures in the regions containing high-pressure phases Coesite present in regions which are collapsed pores has a unique texture, not previously reported for a shock-formed phase: the grains are equidimensional and form a mosaic pattern characteristic of products of high-temperature recrystallization In strongly shocked rocks (estimated pressure P <250 kb) quartz contains abundant glass lamellae, identical to optical “planar features” except that they are so closely spaced that they would not be resolved optically Vesicular glassy regions in strongly shocked rocks contain remnants of large (∼5 μm) coesite crystals, indicating that the shock-formed glass in these regions formed by melting of coesite rather than quartz

Rheology of the lithosphere

Abstract: During the quadrennial term 1979–1982, major advances have been made in our knowledge of the rheology of the oceanic lithosphere by the skillful combination of experimental and theoretical rock mechanics, seismology and marine geophysics in increasingly sophisticated models for the flexure of the oceanic lithosphere at seamounts and island chains, along transform faults, and at subduction zones. The relative simplicity of plate bending geometry, thermal history, and mineralogical and chemical compositions of the oceanic plates in these settings make the geophysical observations very powerful constraints on the in situ rheology of the oceanic lithosphere. In the first part of this paper, I review the laboratory work on materials appropriate to the oceanic lithosphere with emphasis on contributions during the quadrennial period and the need for future work. The important results of flexure models incorporating realistic material properties are then summarized.

Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures

Abstract: This handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures emphasizes terrestrial impact structures, field geology, and particularly the recognition and petrographic study of shock-metamorphic effects in terrestrial rocks. Individual chapters include: 1) Landscapes with Craters: Meteorite Impacts, Earth, and the Solar System; 2) Target Earth: Present, Past and Future; 3) Formation of Impact Craters; 4) Shock-Metamorphic Effects in Rocks and Minerals; 5) Shock-Metamorphosed Rocks (Impactities) in Impact Structures; 6) Impact Melts; 7) How to Find Impact Structures; and 8) What Next? Current Problems and Future Investigations.

Geodynamic Significance of Seismic Anisotropy of the Upper Mantle: New Insights from Laboratory Studies

Abstract: Seismic anisotropy is caused mainly by the lattice-preferred orientation of anisotropic minerals. Major breakthroughs have occurred in the study of lattice-preferred orientation in olivine during the past ∼10 years through large-strain, shear deformation experiments at high pressures. The role of water as well as stress, temperature, pressure, and partial melting has been addressed. The influence of water is large, and new results require major modifications to the geodynamic interpretation of seismic anisotropy in tectonically active regions such as subduction zones, asthenosphere, and plumes. The main effect of partial melting on deformation fabrics is through the redistribution of water, not through a change in deformation geometry. A combination of new experimental results with seismological observations provides new insights into the distribution of water associated with plume-asthenosphere interactions, formation of the oceanic lithosphere, and subduction. However, large uncertainties remain regarding the role of pressure and the deformation fabrics at low stress conditions.

Shock metamorphism of quartz in nature and experiment: I. Basic observation and theory*

Abstract: — Quartz, as a ubiquitous mineral constituent of the Earth's crust, displays the greatest variety of well-defined residual shock effects among all rock-forming minerals. It represents an important and most reliable shock barometer and thermometer for terrestrial impact formations. In this paper, the current status of knowledge about the nature, origin, and experimental pressure-temperature calibration of shock-induced deformations and phase transformations is reviewed for natural and experimental shock conditions.