Preface

Precambrian shield of south India is one of the best-studied shield areas of the world. International teams from UK, USA, Germany, France, Sweden, Japan, Sri Lanka and Australia have sent some of their best men to study one or the other aspects of shield geology. The Geological Society of India as a promoter of research has been playing the role of a mediator bringing these various groups together and in publishing their observations from time to time. Liberal financial support extended by the Department of Science and Technology has helped the Society in bringing out special volumes at frequent intervals keeping the interest alive. Much of the earlier work was concentrated on thd-centrat core of the shield constituting the Archaean Granite-Greenstone terrain.

The granulite belt fringing the craton did not receive as much attention as it was a difficult terrain not easily accessible. It is only some of the intrepid adventurers who ventured into the field all alone and furnished some extraordinarily good geological accounts of the difficult terrain the@, had traversed making interesting reading. Incidentally, the Southern Granulite Terrain is the classical area from which the specific rock type'charnockite' was identified and named by Sir Thomas Holland in focussing the attention of petrologists from all over the world on this new rock type. It was Pichaniuthu who reviewed existing literature and presented a very readable account in his book entitled the 'Charnockite Problem'. This book was of special value to the scientific community as it summarized succinctly information on this enigmatic rock type and brought the status of the problem up-to-date. Pichamuthu died in 1990 by which time the granulite character of the charnockite had been established. In the same year the Geological Society of India broucht out a special Memoir on 'Granulites of South India' which provided an excellent survey of the history of investigations in this area that extended over a period nearly 100 years.

This is the background information about the previous work and the role the Geological Society of India had played in bringing, recent advancements in our knowledge on the subject to the notice of students of rnetamorphic petrology.

Information on the granulite belt surrounding the central core was widely scattered in literature and not coherently presented, An attempt to fill up the lacunae in our information base has now been made in the current volume on the Southern Granulite Terrain. Although it covers only a part of the extensive mobile belt, the coverage being confined only to the southern part of the belt, it brings out the many structural complexities of the terrain. The study points to the existence of fragmented and intersected crustal blocks ensembled along a major suture line. Detailed decipherment of the structures requires more intensive studies and geological mapping on a larger scale. The region has some of the highest mountain ranges of the Peninsula, the Nilgiri and the Palani hills, suggesting neotectonism.

As geologists, we are concerned more with the understanding of surface geology with its bewildering complexities. The three dimensional picture provided by the geophysical signatures, in recent times have, however, provided new information on the structure at depth. A clear understanding will emerge only when geologists begin to appreciate the importance of this new knowledge provided. A new generation of geologists who are well-trained both in the practical and theoretical aspects will be in a better position to appreciate the data provided and gain a less hazier knowledge of the different process of crustal evolution witnessed in the terrain.

The Department of Science and Technology has done well in promoting interdisciplinary studies. The data now provided in the series of papers included in this volume will enable geologists of the coming generation to go a step forward in throwing further light on the problem and in providing a more convincing explanation of the crustal history of the segment now studied.

The Southern Granulite Terrain is only a small part of the larger granulite belt surrounding the craton designated in Indian geology as the Eastern Ghat Mobile Belt of early Proterozoic age. A comprehensive study of the entire belt is needed for a better understanding of the different stages of evolution of the Indian continent. Like the Grenville Province of US and Canada and the Limpopo belt of South Africa, the southern Granulite belt of Peninsular India with its extension to the north forming the Eastern Ghat Mobile belt has the potential to become another classical area in understanding the processes operating in the crust and the mantle beneath.

The Geological Society of India is grateful to the Department of Science and Technology for allowing it to bring out one more publication in the series on granulites. This is sure to spawn many new projects aimed at getting a clearer understanding of the structural evolution of the granulite terrain. With his intimate knowledge of the southern granulite terrain, Dr. M. Ramakrishnan has done a commendable job of compiling and editing this Memoir of the Society.

I have no doubt that like the earlier volumes in the series on the Indian Precambrian the current volume will be received with enthusiasm and read with interest.

28 January 2003
B.P. RADHAKRISHNA