Strain Analysis of the Shear Zones of Ambaji Granulite in the South Delhi Terrane of the Aravalli-Delhi Mobile Belt, NW India, and its Implication on the Exhumation of the Mid-lower Crustal Rocks

Abstract

ABSTRACT Kilometer-scale granulite pockets bounded by shear zones occur within low to medium-grade rocks of the Precambrian mobile belts. Emplacement kinematics of such deeper rocks is reflected in the strain pattern of the associated shear zones. We have carried out the strain analysis of the shear zones of the Ambaji granulite in the Neoproterozoic South Delhi Terrane of the Aravalli-Delhi Mobile belt, NW India. The Kui-Chitraseni shear zone is the main strand and the other shear zones imbricates from it. The shear zones record an earlier phase of thrust kinematics in granulite grade that was primarily responsible for exhuming the rocks from the mid-lower crust. Later a strike-slip shearing was superimposed on those shear zones when the retrogression of the granulites took place. Strain and vorticity analysis of strike-slip shear indicates a transpressive strain consisting of pure and simple shear in different proportions, that led to further extrusion of granulite. Strain gradually diminishes towards the termination points of each shear zone and from center to wall. We have modeled the shear zones in the form of a splay which initiated as a leading thrust splay, transformed into a strike-slip transpressional splay, and subsequently as an extensional termination splay. Extensional splay further contributed to tectonic erosion and exhumation of granulite.