Preface

The Expert Committee on "Deep Continental Studies in India" constituted by the Department of Science and Technol- ogy, New Delhi, decided that a review of the present status of knowledge of the deeper sections of the Indian continental, crust is necessary. This task was assigned to me.

A report was prepared and submitted to the DST in November 1988 in fulfilment of the assignment. The report was circulated to major Earth Science Organisations in India and to a number of experts. Based on suggestions received, it was .decided by the DST that the report should be revised, updated -and published. The Geological Society of India when approached showed interest in its publication.

Programmes of Deep Continental Studies have a three- fold significance.

(i) They help generate meaningful data with regard to crustal evolution and geological history and provide the basis for evolving new and original concepts.

(ii) They help in drawing up innovative and result orientedted approaches to identify new and larger potential fields for the search of mineral deposits and at the same time could help negate efforts that are likely to prove infructuous.

(iii) They provide better appreciation of the geodynamics prevailing over different segments of the continental crust and thereby help in a better understanding of the tectonic (seismic) stabilities of different geo-tectonic provinces in the country and better management of environment.

There is a major thrust all over the world with regard to deep lithospheric studies since the last two decades. Extensive integrated geological-geophysical-geochemical investigations are in progress in most of the countries of the world and, as a result, a great deal of experience is being gained in both the generation of data and interpretation. Reference may be made to a few of the major forerunners to these efforts, namely the Transcontinental Geophysical Survey across the United States initiated in 1962, the North American Continent-Ocean transacts taken up in 1979 and the off-shoots of these efforts, namely the Global Geo-science Transect and Europrobe Programmes being now promoted under the International lithosphere programme. Major effortsinvolving seismic reflection profiling of both continental and oceanic lithosphere are going on in many countries and projects of the Consortium of Continental Reflection Profiling (CONCORP), the British Institution of Reflection Profiling Syndicate (BIRPS), the French Continental and Oceanic Reflection Programme (ECORS) and the German Continental Programme (DEKORP) deserve special mention.

The theme of this review, therefore, is not a new one and in India it lias been discussed in many fora with many positive results. Perhaps the most prominent of the past efforts was under the National Upper Mantle Project and the Project CRUMANSONATA launched by the Geological Survey of India, in the late seventies and its successor "Deep Geology Project" initiated in 1981.' But viewed in the context of the new exciting developments in the field of instrumentation and techniques on the one hand and new and continuously evolving concepts of crustal evolution on the other, our knowledge about the deeper Indian crust is little. We have the basic knowhow of most techniques and methods used in imaging the deep interior of the earth and we have the infrastructure necessary to undertake large programmes involving deep crustal experiments in a well-integrated basis. These capabilities lie inevitably distributed in the many national organisations involved in earth science programmes. Many programmes of some relevance to understanding the deeper crust are being pursued by these organisations almost internally and individually. A well coordinated national effort, now set in motion, will bring together the technical expertise in the various organisations, to focus on projects of relevance in tincler5tanc4in- the deeper aspects of the Indian Subcontinent. There is also need to continually update and keep pace with the fast growing technology. Recognising these national requirements, the Department of Science and Technology has, through a recently up-graded Project Advisory and Monitoring Commiittee, organized a number of working groups to genet-ate Multidisciplinary transacts across the Peninsular Shield and the Himalaya. A number of research projects have also been funded, though the inputs are comparatively on a small scale. It is hoped that these efforts now afoot will gain in momentum and help generate larger programmes which will have an impact on furthering the frontiers of knowledge of the earth's interior in general, and that of the Indian continental lithosphere in particular. A broad framework of a major thrust in this regard is present in is report, on the basis of an overall assessment of the current status of our knowledge.

Considering that the techniques used have passed through different levels of sophistication, and that inputs differ widely from region to region in both their type and scale, a total synthesis of alf the information presented in this book has been difficult and could in fact be even misleading. A broad outline of the emerging scenario of the deep continental structure alone is, therefore, attempted in this book. A total synthesis will call for fresh initiatives and separate organised effort.

It has been the endeavour of the author to capture the major details of the extremely wide spectrum of past contributions. It is nevertheless possible that some significant contributions have been lost sight of inadvertently. The author would be grateful if any such omissions are brought to his notice. It is, however, hoped that any such omissions will not seriously impair the total picture of the emerging scenario of crustal structure, though, indeed, they would blur the view of some small areas.

The book primarily deals with the Indian region but some brief references to some of the adjoining areas have been felt necessary because of geological continuity. The accounts relating to these regions are, however, not intended to be comprehensive.