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Emplacement kinematics of nepheline syenites from the terrane boundary shear zone of the eastern ghats mobile belt, west of Khariar, NW Orissa: Evidence from meso- and microstructures

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Title Emplacement kinematics of nepheline syenites from the terrane boundary shear zone of the eastern ghats mobile belt, west of Khariar, NW Orissa: Evidence from meso- and microstructures
 
Creator BISWAL, TK
AHUJA, H
SAHU, HS
 
Subject deformation
india
nepheline syenite
terrane boundary shear zone
eastern chats mobile belt
magmatic fabric
synkinematic
emplacement
 
Description Nepheline syenite plutons emplaced within the Terrane Boundary Shear Zone of the Eastern Ghats Mobile Belt west of Khariar in northwestern Orissa are marked by a well-developed magmatic fabric including magmatic foliation, mineral lineations, folds and S-C fabrics. The minerals in the plutons, namely microcline, orthoclase, albite, nepheline, hornblende, biotite and aegirine show, by and large, well-developed crystal faces and lack undulose extinction and dynamic recrystallization, suggesting a magmatic origin. The magmatic fabric of the plutons is concordant with a solid-state strain fabric of the surrounding mylonites that developed due to noncoaxial strain along the Terrane Boundary Shear Zone during thrusting of the Eastern Ghats Mobile Belt over the Bastar Craton. However, a small fraction of the minerals, more commonly from the periphery of the plutons, is overprinted by a solid state strain fabric similar to that of the host rock. This fabric is manifested by discrete shear fractures, along which the feldspars are deformed into ribbons, have undergone dynamic recrystallization and show undulose extinction and myrmekitic growth. The shear fractures and the magmatic foliations are mutually parallel to the C-fabric of the host mylonites. Coexistence of concordant solid state strain fabric and magmatic fabric has been interpreted as a transitional feature from magmatic state to subsolidus deformation of the plutons, while the nepheline syenite magma was solidifying from a crystal-melt mush state under a noncoaxial strain. This suggests the emplacement of the plutons synkinematic to thrusting along the Terrane Boundary Shear Zone. The isotopic data by earlier workers suggest emplacement of nepheline syenite at 1500 + 3/ - 4 Ma, lending support for thrusting of the mobile belt over the craton around that time.
 
Publisher INDIAN ACADEMY SCIENCES
 
Date 2011-08-02T03:11:10Z
2011-12-26T12:53:39Z
2011-12-27T05:40:23Z
2011-08-02T03:11:10Z
2011-12-26T12:53:39Z
2011-12-27T05:40:23Z
2004
 
Type Article
 
Identifier PROCEEDINGS OF THE INDIAN ACADEMY OF SCIENCES-EARTH AND PLANETARY SCIENCES, 113(4), 785-793
0253-4126
http://dspace.library.iitb.ac.in/xmlui/handle/10054/8636
http://hdl.handle.net/10054/8636
 
Language en