Microstructural variations in quartzofeldspathic mylonites and the problem of vorticity analysis using rotating porphyroclasts in the Phulad Shear Zone, Rajasthan, India

Sengupta, Sudipta; Chatterjee, Sadhana M.

doi:10.1002/9781118844953.ch9

Cited by 5 publications

(3 citation statements)

References 28 publications

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“…However, the stretching along x axis is considerably large compared to y axis. This suggests a general flattening type of deformation ( X > Y > 1 > Z ) across the shear zone (Sengupta & Chatterjee, ; Sengupta & Ghosh, ). Mapping of PSZ along its strike length of about 200 km reveals that at some places the orientation of the shear zone deviates from its regional NE‐SW trend.…”

Section: Phulad Shear Zonementioning

confidence: 99%

“…We have applied this PHD method to calculate the sectional kinematic vorticity number, W n value in the deformed variety of Phulad granite (Figure a). Calculations are done in mesoscopic scale as PHD method can be misleading in microscopic scale (Sengupta & Chatterjee, ). W n is calculated on PHD net by plotting the aspect ratio ( R = long/short axis) and angle φ ( φ = angle between the long axis of the clast and trace of foliation on XZ section).…”

Section: Kinematic Vorticity Analysismentioning

confidence: 99%

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Mid‐Neoproterozoic Tectonics of Northwestern India: Evidence of Stitching Pluton along 810 Ma Phulad Shear Zone

et al. 2020

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In northwestern India, Phulad Shear Zone (PSZ,~810 Ma) demarcates the boundary between South Delhi Fold Belt to the east and Marwar craton to the west. This shear zone has regional NE-SW trend with small bends of N-S orientations. PSZ is characterized by steep southeasterly dipping mylonitic foliation with steep oblique stretching lineation. The PSZ has developed in a ductile transpression with top-to-the-NNW reverse sense of movement associated with a component of sinistral-slip movement on horizontal section. The 200 by 6 km porphyritic Phulad granite occurs along and across the PSZ, and it is variably deformed. Phulad granite shows evidence of magmatic foliation with preservation of parallel alignment of euhedral feldspars phenocrysts and microgranitoid enclaves. The feldspar phenocrysts show simple twin interfaces parallel to the direction of elongation. This granite also shows development of solid-state foliation parallel to this magmatic foliation. Detailed study of structural elements suggests that Phulad granite has formed during the regional deformation in the country rock shear zone prior to its complete crystallization. Our data indicate that the releasing bends of N-S orientation within the PSZ have provided the space required for emplacement of Phulad granite in a transpressional regime. EPMA U-Pb-Th monazite and U-Pb LA-ICP-MS zircon ages in Phulad granite indicate a magmatic age of 819.1 ± 4 and 818 ± 18 Ma, respectively. PSZ represents the suture along which Marwar craton accreted with remaining India to form the Greater India landmass. The present study suggests that Phulad granite acted as a stitching pluton during this suturing along PSZ at 810-820 Ma.

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Section: Phulad Shear Zonementioning

confidence: 99%

Section: Kinematic Vorticity Analysismentioning

confidence: 99%

Mid‐Neoproterozoic Tectonics of Northwestern India: Evidence of Stitching Pluton along 810 Ma Phulad Shear Zone

et al. 2020

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“…The aspect ratio of feldspar porphyroclasts in the quartzofeldspathic mylonites in the XZ and YZ sections suggests a flattening type of deformation (Figure g). Evidences of stretching in both XZ and YZ sections indicate a three‐dimensional strain with a component of flattening across the shear zone [ Sengupta and Ghosh , ; Sengupta and Chatterjee , ]. Taken together, these features indicate that the shear zone developed during top‐to‐the‐west reverse sense of movement in a transpression regime, i.e., in addition to simple shear there is a strong component of compression across the shear zone.…”

Section: Structures In the Phulad Shear Zonementioning

confidence: 99%

Significance and dynamics of the Neoproterozoic (810 Ma) Phulad Shear Zone, Rajasthan, NW India

et al. 2017

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The Phulad Shear Zone (PSZ) in northwestern India demarcates the boundary between Grenvillian age para‐metamorphics of the South Delhi Fold Belt (SDFB) to the east and variably deformed Neoproterozoic granitoids of the Marwar Craton to the west. In calcareous and quartzofeldspathic mylonites in and around Phulad, the shear zone is characterized by steep SE dipping mylonitic fabric and a steep oblique stretching lineation. The shear zone is developed in a ductile regime with top‐to‐the‐west reverse sense of movement coupled with pronounced flattening across the PSZ. MnNCKFMASH pressure‐temperature pseudosection analysis of closely spaced specimens of garnet‐bearing mica schists reveals that the stabilization of syn/post‐garnet porphyroblasts in the hanging wall experienced near‐isothermal decompression followed by cooling in the retrograde arm of a clockwise P‐T path. The retrieved P‐T paths are consistent with reverse motion of SDFB mica schist over the cratonic foreland. U‐Th‐Pb (total) monazite age determinations in hanging wall mica schists indicate that reverse motion on the PSZ occurred at 810 ± 6 Ma. The pre‐shearing Grenvillian age (~970 ± 9 Ma) metamorphic monazites of the SDFB occur as embayed cores, in the interiors of younger monazite grains. Intense high‐temperature deformation and the emplacement of mica‐bearing pegmatites during reverse shearing caused recrystallization of monazites by dissolution‐precipitation, mantling older monazites in the hanging wall SDFB schists. It is suggested that the PSZ may represent a terrane boundary shear zone along which the Greater India landmass accreted with the Marwar Craton at ~810 Ma.

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Interpretation of deformation microstructures in syntectonic granite: insights from Phulad granite, Rajasthan, NW India

Sarkar,

Manna,

Chatterjee

et al. 2023

Geosci J

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Microstructural variations in quartzofeldspathic mylonites and the problem of vorticity analysis using rotating porphyroclasts in the Phulad Shear Zone, Rajasthan, India

Cited by 5 publications

References 28 publications

Mid‐Neoproterozoic Tectonics of Northwestern India: Evidence of Stitching Pluton along 810 Ma Phulad Shear Zone

Mid‐Neoproterozoic Tectonics of Northwestern India: Evidence of Stitching Pluton along 810 Ma Phulad Shear Zone

Significance and dynamics of the Neoproterozoic (810 Ma) Phulad Shear Zone, Rajasthan, NW India

Interpretation of deformation microstructures in syntectonic granite: insights from Phulad granite, Rajasthan, NW India

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