Deformational and Crystallization History of the Delhi Group Rocks, Around Narnaul, Haryana, India

Abstract

The regional metamorphic rocks of Precambrian age belonging to the Delhi Group, around Narnaul, show complex deformational-crystallization history. The first deformation phase, F₁ of Delhi orogeny produced isoclinal folds overturned towards southeast plunging in NNE-SSW directions associated with most pervasive foliation S₁. The later deformation phases, F₂, tight to open folds, and F₃, open folds produced crenulation cleavages S₂ and S₃ (rare). These three deformational events have been correlated with the crystallization periods of the more important minerals in pelitic schists and amphibolites.

The study reveals that mineral assemblages were identical during the first and second deformation phases. The index minerals garnet, staurolite, kyanite, hornblende started forming either during F₁ folding or immediately after F₁ and continued till the close of F₂ folding with incipient crystallization of micas during F₃ phase. Mineral assemblages in the pelitic schists display a single staurolite-kyanite zone. Mineralogical reactions ,indicate metamorphism under amphibolite condition below 650°C with minimum temperature 540°C and pressure 5.5 kb (P_L =P_total) in this part of the Aravalli belt.