Improved methods for quantitative analysis of three-dimensional porphyroblastic textures

New data-processing methods for making three-dimensional measurements in volumetric data sets, described in a companion paper, are applied here for quantitative textural analysis of porphyroblastic rocks. In a reexamination of a suite of garnetiferous rocks from the Picuris Mountains, New Mexico, Wh...

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Bibliographic Details
Published in:Geosphere (Boulder, Colo.) Colo.), 2005-08, Vol.1 (1), p.42-59
Main Authors: Ketcham, Richard A, Meth, Charna, Hirsch, David M, Carlson, William D
Format: Article
Language:English
Subjects:
BLOB3D
computed tomography
computer programs
crystallization
Crystals
data acquisition
data processing
garnet group
graphic methods
histograms
imagery
Impingement
mechanism
metamorphic rocks
Mineralogy
Mountains
nesosilicates
new methods
Nucleation
Order disorder
orthosilicates
porphyroblastic texture
quantitative analysis
Rocks
silicates
size distribution
statistical analysis
statistical distribution
Texture
textures
Three dimensional
three-dimensional models
tomography
visualization
X-ray data
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Summary:New data-processing methods for making three-dimensional measurements in volumetric data sets, described in a companion paper, are applied here for quantitative textural analysis of porphyroblastic rocks. In a reexamination of a suite of garnetiferous rocks from the Picuris Mountains, New Mexico, Whitt Ranch, Texas, and Mica Dam, British Columbia, signals that in earlier studies indicated ordering of porphyroblast nucleation sites and competition for nutrients are significantly altered but generally confirmed in the improved data. Better-resolution tomographic imagery greatly enhances the observation and measurement of small crystals, in some cases substantially modifying the shape of the crystal size distributions. The enhanced analysis also enables detection of instances of strong impingement among neighboring porphyroblasts that were probably previously interpreted as single crystals, which may have spuriously enhanced ordering signals. Overall the results of this study corroborate earlier findings of diffusion- controlled nucleation and growth of garnet in the specimens examined. They also document, however, the critical importance of high-quality data, which are required to ensure that subtle mechanistic signals can emerge from statistical noise and to ensure that failure of crystal impingement to be detected or preserved does not generate a bias toward ordering.
ISSN:1553-040X
1553-040X
DOI:10.1130/GES00002.1