|Title:||Strain estimation from single forms of distorted fossils - A computer graphics and MATLAB approach|
Rastogi, Vipul K.
|Published in:||Journal of the Geological Society of India|
|Abstract:||Most of the existing methods of strain analysis can estimate strain in a single form of distorted brachiopod, or trilobite provided independent evidence, such as the association of the fossil with cleavage and/or stretching lineation is available for inferring the direction of maximum principal strain. This article proposes a simple computer graphics based method and its MATLAB code that determine the minimum amount of strain in a single distorted fossil form even if data for inferring the maximum principal strain direction are lacking. Our method is a rapid computer-graphics alternative to some of the existing analytical methods. In a distorted fossil form of original bilateral symmetry, the relative senses of angular shears along the hinge line and the median line are mutually opposite to each other. It follows, therefore, that the maximum principal strain direction lies within the acute angle between the hinge and the median lines in the plane of the fossil. Using this principle, our method performs several simulations such that each simulation retrodeforms the distorted fossil by assuming a particular orientation, lying within the acute angle between the hinge line and the median line, as the potential direction of the maximum principal strain. Each simulation of retrodeformation yields a potential strain ratio. The distribution of all the potential strain ratios, obtained by assuming different orientations as the potential directions of the maximum strain, is typically a parabola-like curve with a distinct vertex that corresponds to the minimum amount of strain in the distorted fossil. An entirely computer graphical approach is somewhat time-intensive because it involves a large number of retrodeformational simulations. We, therefore, give a MATLAB code, namely, the Minstrain, that rapidly retrodeforms the fossil and determines the minimum strain with precision. © GEOL. SOC. INDIA.|
|Citation:||Journal of the Geological Society of India (2010), 75(1): 89-97|
|Author Scopus IDs:||11840393900|
|Author Affiliations:||Shah, J., Schlumberger Asia Services Limited, Goregaon(E), Mumbai - 400067, India|
Srivastava, D.C., Department of Earth Sciences, IIT Roorkee, Roorkee - 247 667, India
Rastogi, V., Department of Physics, IIT Roorkee, Roorkee - 247 667, India
Ghosh, R., Department of Earth Sciences, IIT Roorkee, Roorkee - 247 667, India
Aditi, P.A.L., Shell Technology India, Bangalore - 560 048, India
|Funding Details:||Acknowledgements: We thank Terry Engelder (Pennsylvania State University) for drawing our attention to the common occurrence of single forms of distorted fossils in rocks that are not sufficiently deformed/metamorphosed for development of cleavage/lineation. We also thank Sue Treagus and Kieran Mulchorne for suggesting improvements in the manuscript and, to the journal referees, Bruce E. Hobbs and Declan G. De Paor for giving constructive suggestions. Both Kieran Mulchrone and Declan G. De Paor drew our attention to the possible analytical solutions. Our thanks are also due to Manish Mamtani for inviting us to contribute this article and for the efficient editorial handling. We acknowledge Department of Science and Technology (ESS section), Government of India for funding this project.|
|Corresponding Author:||Shah, J.; Schlumberger Asia Services Limited, Goregaon(E), Mumbai - 400067, India|
|Appears in Collections:||Journal Publications [ES]|
Journal Publications [PH]
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