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

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...

Full description

Saved in:
Bibliographic Details
Published in:Tectonics (Washington, D.C.) D.C.), 2017-08, Vol.36 (8), p.1432-1454
Main Authors: Chatterjee, Sadhana M., Roy Choudhury, Manideepa, Das, Subhrajyoti, Roy, Alip
Format: Article
Language:English
Subjects:
clockwise P‐T path
Cores
Cratons
Decompression
Deformation
Dynamics
Fabrics
Garnet
Geological time
Greater India
Marwar Craton
mid‐Neoproterozoic
Monazite
Phulad Shear Zone
Plate tectonics
Precipitation
Schists
Seismology
Shear zone
South Delhi Fold Belt
Temperature
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary: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. Key Points Phulad Shear Zone in NW India developed in a ductile transpressive regime with a top‐to‐the‐west reverse sense of movement In situ monazite age dating suggests that shearing occurred at 810 Ma, along a clockwise P‐T path We suggest PSZ a terrane boundary along which the Greater India accreted with the Marwar Craton at ~810 Ma
ISSN:0278-7407
1944-9194
DOI:10.1002/2017TC004554