Deformation of footwall rock of Phulad Shear Zone, Rajasthan: Evidence of transpressional shear zone

Abstract

Delhi Fold Belt in Rajasthan is a northeasterly striking ductile shear zone with a well developed mylonitic foliation (035/70E) and a downdip stretching lineation. The deformation in the PSZ has developed in a transpressional regime with thrusting sense of movement. The northeastern unit, i.e., the hanging wall contains a variety of rocks namely calc-silicates, pelites and amphibolites and the southwestern unit, i.e., the footwall unit contains only granitic rocks. Systematic investigation of the granites of the southwestern unit indicate a gradual change in the intensity of deformation from a distance of about 1 km west of the shear zone to the shear zone proper. The granite changes from weakly deformed granite to a mylonite/ultramylonite as we proceed towards the PSZ. The weakly deformed granite shows a crude foliation with the same attitude of mylonitic foliation of the PSZ. Microscopic study reveals the incipient development of C and S fabric with angle between C and S varying from 15 • to 24 •. The small angle between the C and S fabric in the least deformed granite variety indicates that the deformation has strong pure shear component. At a distance of about 1 m away from the PSZ, there is abrupt change in the intensity of deformation. The granite becomes intensely foliated with a strong downdip lineation and the rock becomes a true mylonite. In mesoscopic scale, the granite shows stretched porphyroclasts in both XZ and YZ sections indicating a flattening type of deformation. The angle between the C and S fabric is further reduced and finally becomes nearly parallel. In most places, S fabric is gradually replaced by C fabric. Calculation of sectional kinematic vorticity number (W n) from the protomylonitic and mylonite/ultramylonite granites varies from 0.3 ± 0.03 to 0.55 ± 0.04 indicating a strong component of pure shear. The similarity of the geometry of structures in the PSZ and the granites demonstrates that the deformation of the two units is broadly synchronous and the deformation in both the units is transpressional.

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

“…The footwall portion of PSZ belongs to the Marwar craton that contains variably deformed granitoids rocks. The deformation in these granitoids, neighboring the PSZ, varies from weakly foliated through gneissose to mylonite and ultramylonite (Roy Choudhury et al, ). The mean orientation of the foliation in these granitoids broadly overlaps with that of the mylonites of PSZ.…”

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

“…The mean orientation (53°/75°E) of the mesoscale structures in deformed footwall granodiorites broadly overlaps with that of the mylonitic foliation in the calcareous and quartzofeldspathic mylonites in the PSZ (Figure ). By implication, the deformation that affected both the footwall and the PSZ is broadly synchronous and similar in style [ Roy Choudhury et al ., ].…”

Petrological implications of element redistribution during metamorphism: insights from meta-granite of the South Delhi Fold Belt, Rajasthan, India

“…The PSZ mylonitic foliation has a northeasterly strike and a steep easterly dip with a very strong down-dip stretching lineation. Detailed structural studies indicate that the PSZ developed in a ductile transpressional regime (Ghosh et al 1999;Roy Choudhury et al 2016; with a top-to-the-NNW reverse sense of movement (Ghosh et al 1999;Chatterjee et al 2017Chatterjee et al , 2020. The meta-granite of the present study area belongs to the SDFB and is situated on the hanging wall side of the PSZ, nearly a kilometre east of the proper shear zone (Fig.…”