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GPS Application in the Geological Mapping of Pasupugallu Gabbro Pluton, Eastern Ghats Belt, Andhra Pradesh, India  T.R.K. Chetty National Geophysical Research Institute, Hyderabad, India. Email: chettytrk@yahoo.co.in  J. Nagaraju National Geophysical Research Institute, Hyderabad, India. Abstract Global Positioning System (GPS) is a fast, accurate and cost-effective tool that became an integral part of any geological mapping. In the present study, we have used GPS for a precise and quicker geological & structural mapping of a gabbro pluton, emplaced along the Terrane Boundary Shear Zone (TBSZ) situated between the Eastern Ghats Belt and the East Dharwar craton, Andhra Pradesh, India. A hand-held GPS was employed during the mapping of Pasupugallu gabbro pluton to record the locations of several structural measurements, the extents of dolerite dykes within the pluton, and the pluton boundary. The real-time preliminary geological map, prepared from the GPS software, has been conveniently used for plotting the voluminous structural data and reduced a large amount of time and work. In addition, the application of remote sensing technique has greatly enhanced the existed data. The observed structural features of the pluton strongly suggest its syntectonic nature with the TBSZ kinematics. Introduction Surveying has born out of the curiosity of the people to discover the unexposed lands on the Earth in pre-historic times. Basically, surveying aims at producing a map, a plan or an estimate of an area by recording the measurements such as lengths, directions, etc. of features on the Earth’s surface. Geological surveying/mapping, one of its offshoots, is the systematic examination of any region for geological and economic information (Lahee, 1961). It is the backbone for any geologic, exploration and analytical activity and involves identification of landforms, rock types and structures; and the portrayal of these geologic units and structures on a map with their correct spatial relationship with one another. These maps are needed by a broad spectrum of clients for locating the groundwater, mineral, hazard prone areas, etc. It essentially comprises three components, viz., (a) examination and the interpretation of geological and other related features in the real world, (b) determination of the location of features observed, and (c) plotting of this information on a map. Along with the expansion of known world through navigation, the field of surveying also witnessed several phases of development in its methodology, equipment and map quality. It started initially with simple sketches on terracotta, skin (Mishra & Ramesh, 1989) and reached the stage of using theodolite to aerial methods in the recent times. Surveyors, in the last century, were very much successful in producing a wide range of thematic maps such as toposheets, cadastral maps, etc. by using conventional pain-staking surveying procedures of triangulation and traversing (Fig.1a). The Brunton compass, attached with a clinometer is indispensable for any geological field operation. The other mapping methods are gridding with tape, plane table, prismatic compass surveys, hand level, barometer, etc. The compass and clinometer method, traditionally used in reconnaissance mapping, is employed for measuring dips, strikes and other geological parameters; and distances are often measured by pacing and compass traversing. The grid and tape method is very much useful for small areas, but not for regional surveys. The hand level is employed for differences of elevations within low-dipping strata, and the distance is measured by pacing or by stadia. The barometer method of field surveying involves the measurement of relative elevations and vertical distances. The plane table survey (Fig. 1b) is a possible precise method among these to measure horizontal and vertical distances; and maps will be plotted in the field itself. It consists of a plane table, telescope, plotting scale, map sheets, stadia rod and stadia tables and the determination of location can be done by radiation, intersection, and traversing. 
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