Authors: Tanushree Mahadani, Tapas Kumar Biswal
Abstract: The granite mylonite and deformed Gabbronorite-
basic-granulite from Kengora shear zone in
South Delhi Fold Belt shows the contribution of various
deformation mechanisms to the strain geometry that
developed during upper amphibolites/ granulite facies
metamorphism in thrust related shear zones. The rocks
contain good strain markers like well-defined mylonitic
foliation, stretching lineation, asymmetric
porphyroclast, quartz and feldspar ribbon, mica fish.
The shear zone shows NW thrust slip character.
Dynamically recrystallised quartz and feldspar grains
show strain ratios varying from 1.08 to 2.85 for X/Z
sections and 1.06 to 1.95 for Y/Z sections. Using these
strain ratios the Logarithm Flinn plot was drawn, which
shows an apparent flattening strain with volume loss for
all the samples. The volume loss is proportional to the
strain rate and thus progressively increases towards the
centre of the shear zone. The shear strain varies (0.07 to
4.95) across the shear zone and is maximum in the
ultramylonite zone. The angular displacement also
varies along the strike of the shear zone (1.7-1.8 km).
Keywords: Aravalli Delhi Mobile Belt, ductile shear zone,
mylonite, South Delhi Fold Belt.