Consider the following statements : 1. The Achaean rock system is the oldest rock system of India. 2. The most common Achaean rock is gneiss. 3. The Dharwar system belongs to the later part of Achaean system. Choose the correct answer from the options given below :

Archean Rock System

• The Geological Survey of India has classified rock systems of the country into 4 major divisions:
  • The Archaean Rock System
  • The Purana Rock System
  • The Dravidian Rock System
  • The Aryan Rock System
• The Archean Rock System is the oldest rock system of India. Hence, statement 1 is correct.
• The earliest phase of tectonic evolution was marked by the cooling and solidification of the upper crust of the earth’s surface in the Archaean era (prior to 2.5 billion years; Precambrian Period) which is represented by the exposure of gneisses and granites, especially on the Peninsula.
• These form the core of the Indian Craton and are known as the ‘Basement Complex’ as they form the base of new layers.

The Archaean group of rocks consists of two systems-

• Archaean System: Granites and Gneisses,
• Dharwar System: First Sedimentary Rocks. Hence, statement 3 is correct. Found in abundance in the Dharwar district of Karnataka and economically the most important rocks because they possess valuable minerals like high-grade iron-ore, manganese, copper, lead, gold, etc
• Gneiss — Mineral composition varies from granite to gabbro. This is the most common Archean rock. Hence, statement 2 is correct.
• Schists — mostly crystalline, include mica, talc, hornblende, chlorite, etc.