GEOMATICS AND THE GEOTHERMAL PROSPECTS – PUDUKKOTTAI DISTRICT, TAMIL NADU, INDIA. S.Gunasekaran and SM.Ramasamy Centre for Remote Sensing Bharathidasan University Tiruchirappalli, Tamil Nadu BACKGROUND The Geothermal resources are mostly found only in younger folded mountains, soft sediments and in zones of active tectonics. The Geological Survey of India (Anon, 1972) has brought out a GEOTHERMAL ATLAS for the Indian subcontinent and in which they inferred that the Geothermal resources are mostly found in The Himalayas and other areas of active tectonics in India. Bakliwal and Ramasamy (1989) have inferred geothermal resources along NE-SW trending active faults in Sawaimadhopur area, Rajasthan. Similarly in parts of Central India and Western India too, geothermal springs were reported along active faults by many workers. Keeping the above as a clue, the present Remote Sensing based study was undertaken to identify the probable geothermal locales in Pudukkottai district. Aim & Objectives: To identify the Probable areas of Geothermal Prospects using (ii) Remote Sensing revealed Geo-system Anomalies and the detection of Active Faults (ii) Analysis of Groundwater Temperature Anomalies (iii) Integration of both to locate the Probable Geothermal targets LITHOLOGY LINEAMENTS LITHO-TECTONICS DRAINAGE ANOMALIES GROUNDWATER TEMPERATURE ACTIVE FAULTS GROUNDWATER TEMP. ANOMALIES PROBABLE ZONES FOR GEOTHERMAL RESOURCES LITHO SYSTEMS Source : Geological Survey of India Lithologically, the area comprises three major lithotectonic blocks A - The Crystallines of Archaeozoics age in the West, B - The Mio-Pliocene Sandstone /Cuddalore Sandstone are separated by in the Centre and C - The Quaternary sediments in the East. Lineaments and Faults LITHO-TECTONICS The western crystallines and the central Mio-Pliocene which has been inferred to be active and continues all along the Tamil Nadu coast from Chennai in the North North-East to Cape Comorin in the South. The other major lineaments fell in N-S, NE-SW, NW-SE and E-W directions GEOTHERMAL PROSPECTING Mapping Active Faults using Drainage Anomalies The various drainage anomalies viz: Radial, Annular, Migratory and Eyed drainages, Compressed Meanders, etc. were interpreted in detail using raw and digitally processed satellite data as these can provide information on the tectonic movements. Annular Drainages Such annular drainages were mostly found whole these orthogonally cross the North-South aligned Mio-Pliocene Sandstone, which indicated the uplift of the sandstones along N-S and E-W faults. Deflected Drainages Such an interpretation showed that NNW-SSE and NW-SE lineaments have deflected the drainages more, followed by NNE-SSW and NE-SW trending lineaments. From the same it was concluded that the NNW-SSE to NW-SE and NNE-SSW to NE-SW oriented lineaments are tectonically active with area. Eyed Drainages In the present study area, eyed drainages were interpreted using IRS P6 and Survey of India toposheet data sets and these eyed drainages were invariably found to be bisected by the orthogonally / obliquely aligned lineaments indicating tectonic subsidence along these lineaments. Compressed Meanders The otherwise normally flowing drainages when anomalously or abruptly exhibit compressed flow in a restricted zone, the same are interpreted as COMPRESSED MEANDERS. The various drainage anomalies like annular, deflected, eyed, compressed meanders etc., showed that the geological processes are very active in the recent years with E-W and N-S block faulting, NE-SW sinistral and NW-SE dextral strike slip faulting Groundwater Temperature Anomalies Subsequent to the detection of active faults, the groundwater temperature anomalies were analyzed. As far as the known geothermal resources were concerned, the same were reported from two locations only (Kalangudi village and Nartamalai). Hence, in order to study the temperature variations of groundwater temperature measurements were made in between 5:00 am and 10:30 am in groundwater from nearly 300 dug and dug cum bore wells distributed in a near grid pattern in the area. From the same temperature contours were drawn by and the zones of temperature high (A-G, Fig.4) and temperature maxima axes (H, I and J, Fig.4) were mapped, the former at the contours of peak values and the latter by drawing a line along the elliptical contours of maximum values Fig.4). While such high temperature wells were found in seven locations from amongst 300 wells, the temperature maxima axes were found with N-S, NE-SW and NW-SE orientation. The integration of the GIS layer having the 2 known geothermal springs, the 7 high temperature wells (A-G, Fig.5) and the 3 high temperature maxima axes (H-J, Fig.5) with the GIS layer an lineaments and litho-tectonic blocks, it was found that the high temperature wells (A and B) fall in close proximity to NNE-SSW trending Crystalline–Tertiary boundary fault. Similarly, the high temperature wells C, D and E as well as the N-S temperature maxima axes (H) showed coincidence with the N-S contact zone of the dissected and undissected Tertiary Sandstones and the contact of the uplifted and subsiding deltas of Avadaiyarkovil area (Fig.5) which has been inferred to be a major active block fault in the present study area. Probable Geothermal Prospects As far as lithology is concerned, the NNE-SSW trending lithotectonic contact between Crystalline and Tertiary along PudukkottaiTirumayam and the N-S fault between the dissected and undissected Tertiary (Mio-Pliocene) Sandstone and the uplifted and subsiding deltas were buffered out as promising corridors for Geothermal Resources inventory and management. Secondly, N-S and NE-SW faults have gained next priority from the above analysis. N-S Dissected & Undissected Contact Zone Undissected Zone NE-SW Crystalline –Sedimentary Contact Zone Dissected Zone Subsiding Deltas Uplifted Deltas CONCLUSION In the present research study has brought out a unique methodology for mapping the geothermal locals using the active faults and the groundwater temperature maxima.
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