| Abstract |
Several magmatic activities occurred in India during the Precambrian and Post Carboniferous Eras, as represented by granites, basalts and pegmatites. Northern parts of India including Ladakh, Zanskar, Uttarkhand, Himachal Pradesh, and Madhya Pradesh were loci of intense intrusive activity. This is represented by granites of different ages varying from 5-477 Ma. Meanwhile, Precambrian igneous activities were widespread across the country. The Precambrian gneiss invariably forms the stratigraphic basement unit in India. A variety of older granites have intruded into this basement. Although the granite outcrop is discrete, gravity and aeromagnetic anomaly maps indicate that these granites occupy a large area below the sediment and Deccan volcanic cover. In certain areas, they form the basement of Paleozoic (e.g. Gondwana) and Cenozoic (e.g Deccan basalt) formations. These granites occupy an area of about 150,000 km2, extend to great depths, and sometimes form large batholiths several kilometers thick. The most significant feature of these granites is that they drive all the hydrothermal systems in the country. The heat production capacity of these granites varies from about 3-5 W/m3. Prolonged circulation and intense water-rock interaction processes are indicated by high 4He content, low 4He/3He ratio, and high fluoride content in the thermal water. Even though the west coast thermal circulation is thought to be in the Deccan volcanic flows, recent reports on the presence of 140 Ma granite below the Deccan volcanic flows does not preclude major thermal fluid circulation in a granite reservoir. Even in places where natural fluid circulation is not present, these high heat generating granites can be considered hot dry rocks with a high potential to generate electricity. Considerable EGS potential exists even in regions where hydrothermal systems do not exist (e.g. Tamil Nadu). Assessment has been carried out on the power producing capacity of thee granites using U, Th and K content. For example, estimates on a small volume of granite from northern India indicate that there is potential to generate a minimum of 61,160 x 1012 kWh. Perhaps in the future, EGS may help to make India energy independent and to eliminate its 78,577 MWe deficit. |