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GPS Application in the Geological Mapping of Pasupugallu Gabbro Pluton, Eastern Ghats Belt, Andhra Pradesh, India
However, these laborious methods of mapping and collecting geological data, and the hard copy cartography have made the geological mapping a slow, long and cumbersome process. There are several problems associated with the triangulation, such as fixation of permanent markers in the field, and the bearings at large distances, etc. Many of these instruments are not easily portable, and needs more manpower. Moreover, all these methods need to have lot of measurements within short intervals for better accuracy and the data should undergo several correction procedures. The accuracy by these methods is also ambiguous, since it depends on the type of equipment used, the nature of survey and the skills of the people engaged in the complete operation. Inaccurate representation and misorientation of geological datasets generated by these methods can lead to the misunderstanding of the geological process and wrong interpretations.
The era of Geospatial technologies in geological mapping The complications associated with convention mapping techniques were greatly reduced with the advent of geospatial technologies like Global Positioning System (GPS), Geographic Information Systems (GIS), Remotely Sensed systems (airborne and satellite-based multispectral and radar images) and digital surface systems like Ground-Penetrating Radar in surface and subsurface geological mapping. The introduction of GPS constituted by a constellation of 24 satellites established by U.S. Department of Defence in the 1970s is the onset of the technological revolution, which entered in almost all fields of human life, such as natural sciences, business, entertainment, environment, transportation, etc. The GPS is a space-based, highly accurate and all weather continuous navigation system that enable the user to access the position, elevation, velocity and time anywhere in the world (Thurston et al., 2003). The continuous upgradation and modification in the type of sensors and instrumentation have increased the efficiency of GPS functions, where it provides accurate positions at almost the touch of a button. As such, now-a-days, a hand-held GPS becomes an integral part of routine geological field surveying. It is light, portable, and allows the user to store the spatial (in terms of latitude, longitude and altitude) and aspatial (attributes located at the position). Thus the stored data tables and associated attributes can be constructed in a digital format using the GPS software ‘Mapsource’. Geographical Information Systems (GIS) is a collection of several interconnected programs designed for capturing, editing, transforming, retrieving and presenting the geographically referenced data. The vector data provided by the GPS can be imported to the GIS package to produce a geological or other thematic map. Another technique is the Remote Sensing, which is also widely in use as an additional tool of geological mapping. Apart from the facility of synoptic view than that of aerial photographs, the digital image data provides a high resolution, multi-scale, and multi-spectral readability in even inaccessible regions. It provides the real time data about the targets and detects all kinds of changes on the surface of the Earth. All these advances are fast, better and efficient to record, process, analyze and communicate the geological and other related data with a low cost. Geologic significance of the study area In the present study, we have made use of these state of the art techniques (GPS, GIS and Remote Sensing) for a precise and quicker geological and structural mapping of Pasupugallu layered gabbro pluton, Andhra Pradesh, India (Fig. 1c). The elliptical Pasupugallu pluton is one of several mafic, alkaline and granitic plutons emplaced along the Terrane Boundary Shear Zone (TBSZ) situated between the Eastern Ghats Mobile Belt (EGMB) and the East Dharwar craton (Fig. 2 inset). The site of this pluton is critical in the regional tectonic context, since the TBSZ is an easterly dipping thrust between the EGMB and the Dharwar craton, and represents an ancient cryptic suture with dismembered ophiolite occurrences. This zone consists of highly mylonitised amphibolites, migmatitic gneisses, metapelites and sporadic charnockites. The study of pluton can throw light on the genetic association between the emplacement of magma and TBSZ, and further understanding of the regional tectonics prevailing at the time of emplacement.  Fig.2. Preliminary geological map of Pasupugallu gabbro pluton prepared from the waypoints (around 410) stored in GPS, which have been transferred to the GPS software ‘Mapsource’. (Inset map showing the location of Pasupugallu pluton within the Terrane Boundary Shear Zone (TBSZ) at the western margin of the Eastern Ghats Mobile Belt (EGMB). |