ARCHEAN ROCKS IN INDIA:

The term Archean was introduced by Dana in 1872. The age of Archean rocks  about 4 billion years ago.

• Broadly speaking, all those rocks that are the oldest, have absolutely no evidence of the existence of life (in terms of fossils) and undoubtedly form the essential, foundation rocks for all the next formations in Indian stratigraphy are grouped as Archean.

They occupying rock bottom or basal position in stratigraphy, the Archean rocks are commonly referred to as basement COMPLEX or FUNDAMENTAL GENESIS, the latter term being indicative of their predominantly metamorphic (gneissic)structure altogether the areas of their development.

Geologically, these are located at the bottom of the Cambrian system of rocks that are the upward of Eparcheans.

MAP SHOWING THE EXPOSED  AND INFERRED EXTENT OF ARCHEAN rOCKS AND AREAS STUDIED (from peck and valley 2005)

 In terms of your time span, they represent millions of years and are made from igneous rocks and their metamorphosed variations, like gneisses, schists, all highly folded and altered rocks of definite sedimentary origin also are a part of this group developed typically in many areas where they're specially referred to as DHARWAR SYSTEM.

 The Archean form a complex group in Indian stratigraphy, stratigraphically, structurally and petrologically Archean group present diversification that's yet incompletely explained in many respects. Stratigraphically, the rocks are of such extensive development, both in time and space, that these are easily accorded the title of the group.

Within this biggest group of Indian stratigraphy, however, it's been extremely difficult to form out any subdivisions into systems, Epochs, and stages. Even the excellence of this group into the archean system and therefore the DHARWAR SYSTEM is only arbitrary.

In some works is Dharwar system is mentioned along with side Archean system without there being any chronological significance. The Archean system and the dharwar system described below are not ‘systems’ so well understand clearly at the very outset. The dharwar system of Karnataka, therein sense, could also be taken as a subgroup of Archean explored therein type area.

DISTRIBUTION :

The Archean system is most widespread in southern and eastern India through its development in the extra-peninsular region, Especially within the sub-Himalayan ranges is equally of great significance.

They form the core of the inner Himalayas. The Archean rocks of southern India. Especially those developed in Mysore and adjoining regions are specially described as Dharawar system, These shall be discussed separately during a subsequent section. The typically Archean rocks are developed in vast areas of south India, Madhya Pradesh, Chhattisgarh, Orissa, Maharastra, Rajasthan, and sub-Himalayas.

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