GSA Press Release – October 2010 Geosphere Highlights
Boulder, CO, USA – This month’s themed issue, “Advances in 3D imaging and analysis of geomaterials,” edited by Guilherme A.R. Gualda, Don R. Baker, and Margherita Polacci, features papers from the 2009 AGU Joint Assembly session “Advances in 3-D Imaging and Analysis of Rocks and Other Earth Materials.” Studies include 3-D imaging and analysis techniques for Wild 2 comet material returned from the NASA Stardust mission and the first 3-D X-ray scans of crystals from the Dry Valleys, Antarctica.
Keywords: Voxels, microtomography, fractures, NASA Stardust Mission, Wild 2, aerogel, Dry Valleys, Antarctica, geophysics, microearthquakes, Mexico, zircon dating, database, InSAR.
Highlights are provided below. Review abstracts for this issue at http://geosphere.gsapubs.org/.
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Introduction: Advances in 3D imaging and analysis of geomaterials
Guilherme A.R. Gualda, Vanderbilt University, Earth & Environmental Sciences, Station B #35-1805, Nashville, Tennessee 37235, USA
Excerpt: Beginning in the 1970s, the availability of computers led to the development of procedures for computer-assisted acquisition and reconstruction of 3-D tomographic data, in particular using X-rays. X-ray tomography is now a mature technique that is used routinely. It has been applied to a wide array of geomaterials, from rocks to fossils to diverse experimental charges, to name a few. The ability to create 3-D maps with millions to billions of volume elements (voxels) created the challenge of processing and analyzing such large amounts of data. While qualitative observations in 3-D yield significant insights into the nature of geomaterials and geological processes, it is in the pursuit of quantitative data that 3-D imaging shows its greatest potential. The continued improvements in computer capabilities have led to ever more sophisticated procedures for 3D image analysis. The papers in this issue encompass a wide range of topics, from applications of established techniques to a variety of materials, the development of new imaging techniques, and the description of improved imaging and analysis techniques.
3D imaging of volcano gravitational deformation by computerized X-ray micro-tomography
M. Kervyn et al., Dept. of Geology and Soil Science, Ghent University, Krijgslaan 281/S8, 9000 Gent, Belgium
Volcanoes are known to be unstable constructs that can deform gravitationally when they build upon weak sedimentary layers. The structures and velocity of deformation depend on the volcano loading and the properties of the underlying layers. These processes can be studied with scaled laboratory experiments in which volcanoes are simulated by a mixture of sand and plaster. Silicone is used to simulate the weak underlying layers. This team from Belgium and France, lead by M. Kervyn of Ghen University, presents the results of imaging such experiments with X-rays. The micro-tomography technology used in imaging these experiments enables the virtual re-construction of the 3-D shape of the deformed experiment. Virtual cross-sections through the experiment provide a new way to characterize the faults and fissures forming within the experimental volcano during its deformation. Results from a range of experiments with different geometrical characteristics provide a better understanding of the impact of such gravitational deformation, currently recorded at several well-known volcanoes on Earth (e.g. Etna, Kilauea), on the construct’s structure at depth and its potential zones of weakness.
Three-dimensional measurement of fractures in heterogeneous materials using high-resolution X-ray computed tomography
Richard A. Ketcham et al., Dept. of Geological Sciences, Jackson School of Geosciences, 1 University Station C1100, The University of Texas at Austin, Austin, Texas 78712-0254, USA
When present, fractures tend to dominate fluid flow though rock bodies, and characterizing fracture networks is necessary for understanding these flow regimes. Specialized CAT scanning has long been an important tool in imaging fractures in 3-D in rock samples. However, a number of factors have reduced the fidelity of such data, including the natural heterogeneity of real rocks and the limited resolution of CAT scanning. Richard A. Ketcham of The University of Texas at Austin and colleagues present new, general methods for overcoming these problems and extracting the best-quality information possible concerning fracture aperture, roughness, and orientation, even in highly heterogeneous rocks. The methods are also general enough that they can be applied to similar situations, such as measuring mineral veins. This work was funded in part by U.S. National Science Foundation grants EAR-0113480 and EAR-0439806.
Laser scanning confocal microscopy of comet material in aerogel
Michael Greenberg and Denton S. Ebel, Dept. of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, New York 10024, USA
The NASA Stardust mission returned extraterrestrial material from the comet Wild 2 — the first solid sample-return mission since the Apollo era. Particles from the tail of Wild 2 were captured in aerogel, low-density, translucent, silica foam at a relative velocity of 6.1 km per second. Upon impact into the aerogel, particles from the tail of the comet were fragmented, melted, and ablated, creating cavities, or tracks — each of which is unique to the original particle before capture. Michael Greenberg and Denton S. Ebel of the American Museum of Natural History present nondestructive 3-D imaging and analysis techniques for comet material returned from the NASA Stardust mission. The methods described in this paper represent the highest resolution 3-D images of Stardust material to date. The procedures described here will easily extend to other translucent samples in the geosciences.