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Bhatt, S. C.
- Kinematic Framework of Heterogeneous Deformation Within Pratapnagar Thrust Sheet, Bhagirathi Valley, in Lesser Garhwal Himalaya. U.P.
Authors
1 Department of Geology, Delhi University, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 36, No 3 (1990), Pagination: 247-261Abstract
The Pratapnagar quartzite constituting Pratapnagar thrust sheet was subjected to strain analysis Assuming the foliation (S1) in the quartzite as XY plane for strain estimation. sections parallel to XY, XZ and YZ of the quartzite exposed at the base of the Pratapnagar thrust sheet and away from It were prepared The specimens of the quartzite belong to the proximity of the Pratapnagar thrust sheet and witnessed increasing trend of flattening as indicated by two dimensional strain ratio (Rs) The three dimensional finite strain Was higher in intensity (Es = 0676 to 0937) and is marked by oblate type of ellipsoid (k).
In contrast to this, the quartzite located away from the thrust was subjected to progressive plane and constrictional type of strain and the shape of the ellipsoid Was prolate This indicates that away from the thrust the strain was variable but it acquired unidirectional trend with greater amount of intensity giving rise to extreme flattening parallel to Z. The stretching of the quartz grams was maximum along X, more or less, comciding with the NESW trending thrust transport direction.
Keywords
Structure, Bhagrrathi Valley, Himalaya, Garhwal, United Provinces.
- Strain Transition and Microstructural-Fabric Analysis of Qaurtz-Mylonites Exposed within Pratapnagar Nappe Garhwal Himalaya, India
Authors
1 Central Soil and Materials Research Station, New Delhi-16, IN
2 Department of Geology, Delhi Unviersity, Delhi-7, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 43, No 4 (1994), Pagination: 381-394Abstract
The Pratapnagar Thrust sheet in the Lesser Garhwal Himalaya consists of massive, white mylonitized Pratapnagar Quartzite and is delineated at its base by the Pratapnagar Thrust which brings this rock group to rest over the parautochthonous Argillocalc-arenite Group.
The estimated three-dimensional finite strain (̅Σs) in the specimens located close to the Pratapnagar Thrust was 0.937 while away from the thrust it was 0.412. The quartzite exposed within the mylonitized zone of Pratapnagar Thrust underwent non-coaxial (= simple shear) deformation revealed by asymmetrical (unpopulated) C-axes girdles and rotation of mylonitic foliation (S3), lineation (Lm) and C-axes girdles, The variable orientation of C-axes girdles, mylonitic foliation, lineation and microstructural shear indicators (asymmetrical porphyroclasts and pressure shadows) noticed within the rock exposed along the thrust zone indicate sinistral (-ve) sense of shear movement (NE-SW) with respect to N. The quartzite away from the thrust were initialy subjected to coaxial (= pure shear) deformation as is indicated by scattered globular and tabular host quartz grains and symmetrical cross and small circle girdle patterns of C-axes. The microstructural transition and asymmetrical orientation of C-axes fabrics indicate that the mylonitized Pratapnagar Quartzite was formed by deformation under ductile flow and low grade metamorphic conditions.
Keywords
Structural Geology, Garhwal, Himalaya, Uttar Pradesh.- Structural History and Fold Analysis of Basement Rocks around Kuraicha and Adjoining Areas, Bundelkhand Massif, Central India
Authors
1 Department of Geology, Bundelkhand University, Jhansi-284 128, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 72, No 3 (2008), Pagination: 331-347Abstract
The basement consisting of banded to streaky gneisses with inclusion of migmatites, schist, quartzite, amphibolites, mafics/ultramafics, BIF and metasedimentaries are exposed around Kuraicha, Mauranipur and adjoining areas. These Pre-Bundelkhand rocks were deformed during three phases of folding (F1-F3) under the influence of three tectonic episodes (D1-D3). The granitic rocks mainly comprise of large batholithic massif of medium to coarse grained pink granite along with a few lensoidal bodies of porphyritic pink and grey biotite granites.
The F1 folds exhibiting tight to isoclinal geometries are characterized by IC, 4, and 1A types of fold style. The increasing trend of flattening (30-90%) and quarter wavelength/Amplitude (w/4/A) ratio (0.43-0.56) exhibited by F1 folds exposed close to the shear zone, while away from the shear zone the definite decrease (10-60%) in these values is marked. Similar relationship is also noticed in F2 and F3 folds exposed at proximal and distal parts of the shear zone. It reveals that the flattening percentage and W/4/A ratio have inverse relationship with the distance from the shear zone.
The kinematic indicators viz. mylonitic foliation, stretching lineation, asymmetric and rotated porphyroclasts, sheath folds and S-C fabrics observed on mesoscopic scale, strongly support the existence of brittle-ductile shear zone in the study area. These observations also infer that the fabrics in this brittle ductile shear zone, deformed due to moderate to high shear strain under the predominance of nonaxial strain and extensional tectonics in D4 phase of deformation.