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Pal, Aditi
- Pseudotachylites of the Kui-Chitraseni Shear Zones of the Precambrian Aravalli Mountain, Rajasthan
Authors
1 Indian Institute of Technology, Powai, Mumbai - 400 076, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 64, No 3 (2004), Pagination: 325-335Abstract
Cataclasites-pseudotachylites are developed along the Kui-Chitraseni shear zone of the Aravalli Mountain. The pseudotachylites are microlitic belonging to three varieties referred to here as patchy-, vein- and fracture- pseudotachylites. The patchy pseudotachylites are the most dominating type that occur in association with cataclasites and show an increase in abundance from the margin of the shear zone towards the center. Vein pseudotachylites owe their origin to the injection of the patchy variety through extensional fractures. Fracture pseudotachylites, the youngest of all, occur along the late stage shear fractures. Presence of vesicles, flow texture, embayed margin of the clasts in addition to power law distribution of coarser clasts and high values of roundness (0.4) support the melt origin of the pseudotachylites. Ultracataclasis followed by frictional melting of the Erinpura granites along the shear zone is ascribed for the development of the cataclasites and pseudotachylites.Keywords
Pseudotachylites, Melt Origin, Kui-Chitraseni Shear Zone, Aravalli Mountain, Erinpura Granite.
- Strain Estimation from Single Forms of Distorted Fossils - A Computer Graphics and MATLAB Approach
Authors
1 Schlumberger Asia Services Limited, Goregaon(E), Mumbai-400067, IN
2 Department of Earth Sciences, IIT Roorkee, Roorkee-247 667, IN
3 Department of Physics, IIT Roorkee, Roorkee-247 667, IN
4 Shell Technology India, Bangalore-560 048, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 75, No Spl Iss 1 (2010), Pagination: 89-97Abstract
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.
Keywords
Strain, Distorted Fossil, Lineation, Cleavage, MATLAB.References
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